Handbook of Archaeological Sciences, 2 Volume Set [2 ed.] 1119592046, 9781119592044

Table of contents :
Cover
Volume 1
Title Page
Copyright Page
Contents
List of Contributors
Foreword: Archaeological Science and the Big Questions
Introduction
Don Brothwell – An Appreciation
Volume 2
Title Page
Copyright Page
Contents
Index
EULA

Citation preview

About the pagination of this eBook This eBook contains a multi-volume set. To navigate the front matter of this eBook by page number, you will need to use the volume number and the page number, separated by a hyphen. For example, to go to page v of volume 1, type “1-v” in the Go box at the bottom of the screen and click "Go." To go to page v of volume 2, type “2-v”… and so forth.

Handbook of Archaeological Sciences

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Handbook of Archaeological Sciences Volume 1 Second Edition

Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz

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This second edition first published 2023 © 2023 John Wiley & Sons Ltd Edition History © 2009 by John Wiley & Sons Ltd All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz to be identified as the authors of this work has been asserted in accordance with law. Registered Office John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial Office Boschstr. 12, 69469 Weinheim, Germany For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print-­on-­demand. Some content that appears in standard print versions of this book may not be available in other formats. Trademarks: Wiley and the Wiley logo are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries and may not be used without written permission. All other trademarks are the property of their respective owners. John Wiley & Sons, Inc. is not associated with any product or vendor mentioned in this book. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/ or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Library of Congress Cataloging-­in-­Publication Data Names: Pollard, A. M., editor. | Armitage, Ruth Ann, editor. | Makarewicz,   Cheryl A., editor. Title: Handbook of archaeological sciences / edited by A. Mark Pollard,   Ruth Ann Armitage, Cheryl A. Makarewicz. Description: Second edition. | Hoboken, NJ : Wiley, 2023. | Includes   bibliographical references and index. Identifiers: LCCN 2022047004 (print) | LCCN 2022047005 (ebook) | ISBN   9781119592044 (set; cloth) | ISBN 9781394156832 (v.1; cloth) | ISBN   9781394156849 (v.2; cloth) | ISBN 9781119592075 (adobe pdf) | ISBN   9781119592082 (epub) Subjects: LCSH: Archaeology–Methodology. Classification: LCC CC75 .H34 2023 (print) | LCC CC75 (ebook) | DDC   930.1–dc23/eng/20221013 LC record available at https://lccn.loc.gov/2022047004 LC ebook record available at https://lccn.loc.gov/2022047005 Cover Design: Wiley Cover Images: Courtesy of Gordon Turner-Walker; ASVMAGZ/Shutterstock; Xolodan/Shutterstock Set in 9.5/12.5pt STIXTwoText by Straive, Pondicherry, India

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Contents List of Contributors  xi Foreword: Archaeological Science and the Big Questions  xvii Chris Gosden Introduction  xix A.M. Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz Don Brothwell – An Appreciation  xxiii Terry O’Connor

Volume 1 Section 1  Science-­based Dating in Archaeology  1 Christopher Bronk Ramsey 1 Quaternary Geochronological Frameworks  7 Christine S. Lane 2 New Developments in Radiocarbon Dating  25 Lorena Becerra-­Valdivia and Tom Higham 3 Dendrochronology and Archaeology  37 Sturt W. Manning 4 Trapped Charge Dating and Archaeology  69 Maïlys Richard 5 U-­Series Dating in Archaeology  89 Edwige Pons-­Branchu 6 Archaeomagnetic Dating  99 Cathy Batt 7 Amino Acid Dating  119 Kirsty Penkman 8 An Introduction to Tephrochronology and the Correlation of Sedimentary Sequences Using Volcanic Ash Layers  133 Victoria C. Smith and Paul G. Albert

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Contents

Section 2  An Introduction to Quaternary Climate Change and Human Evolution and Adaptation  151 Simon Blockley 9 Ice Core and Marine Sediment Records of Quaternary Environmental Change  159 J.R. McConnell, S.O. Brugger, and N.J. Chellman 10 Insects as Palaeoenvironmental and Archaeological Indicators  187 Stefan Engels and Nicki J. Whitehouse 11 Mammals as Palaeoenvironmental Indicators  211 Julien Louys and Hannah O’Regan 12 Lake and Peat Records of Climate Change and Archaeology  227 P.G. Langdon, A.G. Brown, C.L. Clarke, M.E. Edwards, P.D.M. Hughes, R. Mayfield, A. Monteath, D. Sear, and H. Mackay 13 Archaeological Soil Micromorphology  253 Helen Lewis 14 Pollen and Macroscopic Plant Remains as Indicators of Local and Regional Environments  271 Petra Dark 15 Environmental Controls on Human Dispersal and Adaptation  289 Adrian G. Parker and Simon J. Underdown 16 Holocene Climate Changes and Human Consequences  321 Neil Roberts Section 3  Evolution to Revolution: Human Bioarchaeology is Riding High  339 Charlotte A. Roberts 17 Hominin Evolution  359 Jason J. Gellis and Robert A. Foley 18 Biological Distance  387 Benjamin M. Auerbach 19 Palaeopathology  405 Anne L. Grauer 20 Integrating Bioarchaeology and Palaeodemography  419 Clare McFadden and Marc F. Oxenham 21 Palaeodiet Through Stable Isotope Analysis  437 Tamsin C. O’Connell 22 Preserved Human Bodies  453 Andrew S. Wilson, Isabella Mulhall, Virginie Cerdeira, and Eline M.J. Schotsmans Section 4  Shifting to a Higher Gear: Proteins, Small Molecules, and the Rise of Mass Spectrometry  477 Ruth Ann Armitage, Cheryl A. Makarewicz, and A.M. Pollard 23 Zooarchaeology by Mass Spectrometry (ZooMS)  483 Michael Buckley

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Contents

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24 Archaeological Proteomics  501 Jessica Hendy 25 The Use of Immunological Methods in Archaeology  511 Carney Matheson 26 Lipids in Archaeology  529 Lucy J.E. Cramp, Ian D. Bull, Emmanuelle Casanova, Julie Dunne, Mélanie Roffet-­Salque, Helen L. Whelton, and Richard P. Evershed 27 Archaeological Microbiology  557 Laura S. Weyrich and Vilma Perez 28 Dental Calculus  575 Zandra Fagernäs and Christina Warinner 29 The Biomolecular Archaeology of Psychoactive Substances  591 Mario Zimmermann and Shannon Tushingham

Volume 2 Section 5  Archaeogenetics  607 Terence A. Brown 30 Sex Identification and Kinship Typing of Human Archaeological Remains  613 Terence A. Brown, Konstantina Drosou, and Keri A. Brown 31 Human Populations – Origins and Movement  629 Eva Fernández-­Domínguez 32 Palaeogenomics of Extinct and Archaic Hominins  647 M. Thomas P. Gilbert and Carles Lalueza-­Fox 33 Palaeogenetics and Palaeogenomics to Study the Domestication of Animals  657 Eva-­Maria Geigl 34 Palaeomicrobiology of Human Infectious Diseases  677 Helen D. Donoghue

Section 6  Overview of ‘Biological Resources’ – From Old Debates to Urgent Ecological Dilemmas  697 Amy Bogaard 35 Archaeobotany  701 Carla Lancelotti and Marco Madella 36 Human Impact on Vegetation  715 Ralph Fyfe 37 Zooarchaeology  731 Alan K. Outram

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Contents

38 Coprolites, Gut Contents and Molecular Archaeoparasitology  753 Andrew K.G. Jones and Adrian L. Smith 39 Advances in the Archaeological Study of Invertebrate Animals and Their Products  769 Marcello A. Mannino and Kenneth D. Thomas 40 Archaeological Textiles as Secondary Plant and Animal Products  797 Christel M. Baldia and Ruth Ann Armitage Section 7  Scientific Studies of Inorganic Resources in Archaeology – Overview of Current Status and Prospects  813 Shadreck Chirikure 41 Lithic Exploitation and Usewear Analysis  819 Elspeth Hayes, Richard Fullagar, and Michelle Richards 42 Ancient Binders and Pigments  833 Ioanna Kakoulli and Magdalena Balonis 43 Materials Analysis of Ceramics  867 Nathaniel L. Erb-­Satullo 44 The Archaeometry of Glass  885 Ian C. Freestone 45 Mining and Resource Procurement: Methods and Approaches to the Appropriation of Mineral Raw Materials in Past Societies  911 Thomas Stoellner 46 Making and Using Metals: Contributions from Archaeological Science  935 Marcos Martinón-­Torres 47 Provenancing Inorganic Materials: The Influences of Biography and Mutability  953 A.M. Pollard Section 8  Prospecting Beyond Boundaries: The Irresistible Rise of Remote Sensing in the Twenty-­First Century  963 Chris Gaffney 48 Approaches to Archaeological Surface Survey  969 Joshua Wright 49 Geophysical Survey Techniques  985 Eileen G. Ernenwein 50 Archaeological Remote Sensing  1005 Jesse Casana 51 Geochemical Prospection and the Identification of Site Activity Areas  1025 Karen Milek, Carl Heron, Ruth Ann Armitage, and Nyree Manoukian

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52 Integrating Survey Data  1045 Kenneth L. Kvamme Section 9  Conservation Science in Practice  1063 David Watkinson 53 Defining the Burial Environment  1075 David Gregory and Henning Matthiesen 54 Metallic Corrosion Processes and Information from Corrosion Products  1089 L. da C. Carvalho 55 Post-­Depositional Changes in Archaeological Ceramics and Glass  1103 Nancy Odegaard and Gina Watkinson 56 Diagenetic Alterations to Vertebrate Mineralized Tissues – A Critical Review  1117 Gordon Turner-­Walker Section 10  ‘It’s All in the Numbers’: Quantitative and Computational Approaches in Archaeology  1157 Marcos Llobera 57 Spatial Information in Archaeology  1163 Philip Verhagen 58 Multivariate Analysis in Archaeology  1183 Michael D. Glascock and Brandi Lee MacDonald 59 The Bayesian Inferential Paradigm in Archaeology  1193 Erik Otárola-­Castillo, Melissa G. Torquato, and Caitlin E. Buck 60 Quantification in Zooarchaeology and Palaeoethno(Archaeo)botany  1211 R. Lee Lyman and Steve Wolverton 61 The Use of Kernel Density Estimates on Chemical and Isotopic Data in Archaeology  1227 A.M. Pollard, Qian Ma, A.-­I. Bidegaray, and Ruiliang Liu 62 Forward Modelling and Simulation in Archaeology  1241 Rowan McLaughlin 63 Big Data in Archaeology  1249 Chris Green Index  1261

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List of Contributors Paul G. Albert Department of Geography, Swansea University, Swansea, UK Ruth Ann Armitage Department of Chemistry, Eastern Michigan University, Ypsilanti, MI, USA Benjamin M. Auerbach Departments of Anthropology & Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN, USA Christel M. Baldia NYLAB, Laboratory Scientific Services Directorate, US Customs and Border Protection, Newark, NJ, USA Magdalena Balonis Department of Materials Science and Engineering, Henry Samueli School of Engineering, University of California Los Angeles, Los Angeles, CA, USA Cathy Batt School of Archaeological and Forensic Sciences, University of Bradford, Bradford, UK Lorena Becerra-­Valdivia Oxford Radiocarbon Accelerator Unit, Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK

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Amy Bogaard School of Archaeology, University of Oxford, Oxford, UK Christopher Bronk Ramsey Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK A.G. Brown Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Keri A. Brown Manchester Institute of Biotechnology, The University of Manchester, Manchester, UK Terence A. Brown Manchester Institute of Biotechnology, The University of Manchester, Manchester, UK S.O. Brugger Division of Hydrologic Science, Desert Research Institute, Reno Northern Nevada Science Center, Reno, NV, USA Caitlin E. Buck School of Mathematics and Statistics, University of Sheffield, Sheffield, UK

A.-­I. Bidegaray Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK

Michael Buckley School of Natural Sciences, Manchester Institute of Biotechnology, The University of Manchester, Manchester, UK

Simon Blockley Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, London, UK

Ian D. Bull Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK

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List of Contributors

L. da C. Carvalho School of Archaeology, University of Oxford, Oxford, UK Jesse Casana Department of Anthropology, Dartmouth College, Hanover, NH, USA Emmanuelle Casanova Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK Virginie Cerdeira Wellcome Trust, London, UK N.J. Chellman Division of Hydrologic Science, Desert Research Institute, Reno Northern Nevada Science Center, Reno, NV, USA Shadreck Chirikure School of Archaeology, University of Oxford, Oxford, UK Department of Archaeology, University of Cape Town, Rondebosch, South Africa C.L. Clarke Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Lucy J.E. Cramp Department of Anthropology and Archaeology, University of Bristol, Bristol, UK Petra Dark Department of Archaeology, University of Reading, Reading, UK Helen D. Donoghue Centre for Clinical Microbiology, Division of Infection and Immunity, University College London, London, UK

M.E. Edwards Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Stefan Engels Department of Geography, Birkbeck University of London, London, UK Nathaniel L. Erb-­Satullo Cranfield Forensic Institute, Cranfield University, Cranfield, UK Eileen G. Ernenwein Department of Geosciences, East Tennessee State University, Johnson City, TN, USA Richard P. Evershed Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK Zandra Fagernäs Department of Archaeogenetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany Eva Fernández-­Domínguez Department of Archaeology, Durham University, Durham, UK Robert A. Foley Leverhulme Centre for Human Evolutionary Studies, Department of Archaeology, University of Cambridge, Cambridge, UK Ian C. Freestone Institute of Archaeology, UCL, London, UK

Konstantina Drosou Manchester Institute of Biotechnology, The University of Manchester, Manchester, UK School of Biological Sciences, The University of Manchester, Manchester, UK

Richard Fullagar Centre for Archaeological Science, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, New South Wales, Australia College of Humanities, Arts and Social Sciences, Flinders University, Adelaide, South Australia, Australia School of Social Sciences, University of Western Australia, Perth, Western Australia, Australia

Julie Dunne Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK

Ralph Fyfe School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, UK

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List of Contributors

Chris Gaffney School of Archaeological and Forensic Sciences, University of Bradford, Bradford, UK Eva-­Maria Geigl Institut Jacques Monod, CNRS, Université de Paris, Paris, France Jason J. Gellis Department of Archaeology, Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Cambridge, UK M. Thomas P. Gilbert Center for Evolutionary Hologenomics, The GLOBE Institute, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark Michael D. Glascock MU Research Reactor Center, University of Missouri, Columbia, MO, USA Chris Gosden School of Archaeology, University of Oxford, Oxford, UK Anne L. Grauer Department of Anthropology, Loyola University Chicago, Chicago, IL, USA

P.D.M. Hughes Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Andrew K.G. Jones Department of Archaeology, University of York, York, UK Ioanna Kakoulli Department of Materials Science and Engineering, Henry Samueli School of Engineering, University of California Los Angeles, Los Angeles, CA, USA Kenneth L. Kvamme Department of Anthropology, University of Arkansas, Fayetteville, AR, USA Carles Lalueza-­Fox Institute of Evolutionary Biology, CSIC-­Universitat Pompeu Fabra, Barcelona, Spain Museu de Ciències Naturals de Barcelona, Barcelona, Spain Carla Lancelotti Department of Humanities, Universitat Pompeu Fabra, Barcelona, Spain

David Gregory Department of Research, Collections and Conservation, The National Museum of Denmark, Kongens Lyngby, Denmark

Christine S. Lane Department of Geography, University of Cambridge, Cambridge, UK

Jessica Hendy BioArCh, Department of Archaeology, University of York, York, UK Carl Heron Department of Scientific Research, The British Museum, London, UK

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Tom Higham Oxford Radiocarbon Accelerator Unit, Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK Department of Evolutionary Anthropology, University of Vienna, University Biology Building, Vienna, Austria

Chris Green School of Archaeology, University of Oxford, Oxford, UK

Elspeth Hayes Centre for Archaeological Science, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, New South Wales, Australia

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P.G. Langdon Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Helen Lewis School of Archaeology, University College Dublin, Dublin, Ireland Ruiliang Liu Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK The Department of Asia, British Museum, London, UK

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List of Contributors

Marcos Llobera Department of Anthropology, University of Washington, Seattle, WA, USA

Carney Matheson Department of Anthropology, Griffith University, Brisbane, Queensland, Australia

Julien Louys Australian Research Centre for Human Evolution, Griffith University, Brisbane, Queensland, Australia

Henning Matthiesen Department of Research, Collections and Conservation, The National Museum of Denmark, Kongens Lyngby, Denmark

R. Lee Lyman Department of Anthropology, University of Missouri, Columbia, MO, USA Qian Ma Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK Brandi Lee MacDonald Research Reactor Center, University of Missouri, Columbia, MO, USA H. Mackay Department of Geography, Durham University, Durham, UK Marco Madella Department of Humanities, Universitat Pompeu Fabra, Barcelona, Spain Cheryl A. Makarewicz Institute of Prehistoric and Protohistoric Archaeology, Christian-Albrechts-Universität zu Kiel, Kiel, Germany Sturt W. Manning Cornell Tree Ring Laboratory, Department of Classics, Cornell University, Ithaca, NY, USA The Cyprus Institute, Aglantzia, Cyprus Marcello A. Mannino Department of Archaeology and Heritage Studies, Aarhus University, Højbjerg, Denmark Nyree Manoukian Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK Marcos Martinón-­Torres Department of Archaeology, University of Cambridge, Cambridge, UK

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R. Mayfield Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK J.R. McConnell Division of Hydrologic Science, Desert Research Institute, Reno Northern Nevada Science Center, Reno, NV, USA Clare McFadden School of Archaeology and Anthropology, Australian National University, Acton, Australian Capital Territory, Australia Rowan McLaughlin Hamilton Institute, Maynooth University, Maynooth, Ireland Karen Milek Department of Archaeology, Durham University, Durham, UK A. Monteath Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Isabella Mulhall Irish Antiquities Division, National Museum of Ireland – Archaeology, Dublin, Ireland Tamsin C. O’Connell Department of Archaeology, University of Cambridge, Cambridge, UK Terry O’Connor Department of Archaeology, University of York, York, UK Nancy Odegaard Arizona State Museum, University of Arizona, Tucson, AZ, USA

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List of Contributors

Hannah O’Regan Department of Classics and Archaeology, University of Nottingham, Nottingham, UK Erik Otárola-­Castillo Department of Anthropology, Purdue University, West Lafayette, IN, USA Alan K. Outram Department of Archaeology and History, University of Exeter, Exeter, UK Marc F. Oxenham School of Archaeology and Anthropology, Australian National University, Acton, Australian Capital Territory, Australia Department of Archaeology, School of Geosciences, University of Aberdeen, Aberdeen, UK Adrian G. Parker Human Origins and Palaeoenvironments Research Group, School of Social Sciences, Oxford Brookes University, Oxford, UK Kirsty Penkman Department of Chemistry, University of York, York, UK Vilma Perez Australian Centre for Ancient DNA (ACAD), University of Adelaide, Adelaide, South Australia, Australia ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH), University of Adelaide, Adelaide, South Australia, Australia A.M. Pollard Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK Edwige Pons-­Branchu Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-­CNRS-­UVSQ, Universite Paris Saclay, Gif-­sur-­Yvette, France Maïlys Richard Archéosciences Bordeaux, UMR 6034 CNRS-­Bordeaux Montaigne University, Pessac, France

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Michelle Richards Department of Archaeology and History, La Trobe University, Bundoora, Victoria, Australia Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, School of Culture, History and Language, The Australian National University, Acton, Australian Capital Territory, Australia. Charlotte A. Roberts Department of Archaeology, Durham University, Durham, UK Neil Roberts School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, UK School of Archaeology, Oxford University, Oxford, UK Mélanie Roffet-­Salque Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK Eline M.J. Schotsmans Centre for Archaeological Science, University of Wollongong, Wollongong, New South Wales, Australia De la Préhistoire à l’Actuel: Culture, Environnement et Anthropologie (PACEA), UMR 5199, CNRS-­Université de Bordeaux, Bordeaux, France D. Sear Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Adrian L. Smith Department of Zoology, University of Oxford, Oxford, UK Victoria C. Smith Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK Thomas Stoellner Institute of Archaeological Studies, Pre-­and Protohistory, Ruhr-­University Bochum, Bochum, Germany Research Department, Mining Archaeology, Deutsches Bergbau-­Museum Bochum, Bochum, Germany

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List of Contributors

Kenneth D. Thomas Institute of Archaeology, University College London, London, UK Melissa G. Torquato Department of Anthropology, Purdue University, West Lafayette, IN, USA Gordon Turner-­Walker Department of Archaeology and Anthropology, National Museum of Natural Science, Taichung, Taiwan Shannon Tushingham Department of Anthropology, Washington State University, Pullman, WA, USA Simon J. Underdown Human Origins and Palaeoenvironments Research Group, School of Social Sciences, Oxford Brookes University, Oxford, UK Philip Verhagen Faculty of Humanities, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands Christina Warinner Department of Archaeogenetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany Department of Anthropology, Harvard University, Cambridge, MA, USA David Watkinson Archaeology and Conservation Section, School of History, Archaeology and Religion, Cardiff University, Cardiff, UK Gina Watkinson Arizona State Museum, University of Arizona, Tucson, AZ, USA

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Laura S. Weyrich Department of Anthropology, The Pennsylvania State University, University Park, PA, USA Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, USA Australian Centre for Ancient DNA (ACAD), University of Adelaide, Adelaide, South Australia, Australia ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH), University of Adelaide, Adelaide, South Australia, Australia Helen L. Whelton Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK Nicki J. Whitehouse Archaeology, School of Humanities, University of Glasgow, Glasgow, UK Andrew S. Wilson School of Archaeological and Forensic Sciences, University of Bradford, Bradford, UK Steve Wolverton Department of Geography and the Environment, University of North Texas, Denton, TX, USA Joshua Wright Department of Archaeology, University of Aberdeen, Aberdeen, UK Mario Zimmermann Department of Sociology and Anthropology, University of Puget Sound, Tacoma, WA, USA Department of Anthropology, Washington State University, Pullman, WA, USA

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Foreword: Archaeological Science and the Big Questions Chris Gosden

School of Archaeology, University of Oxford, Oxford, UK

As a discipline archaeology tackles many of the big questions of what it means to be human and how this has changed over time. Such questions include those of ancestry, the relationship between major human populations, the movement of people across the globe, as well as demographic changes and transitions, and also the cultural uses and abuses that can be made of biological differences when thinking about race, gender, and sexuality. How people are born, mature, grow old, and die vary due to the physical and cultural environments in which people live and include notions of care, especially at the beginnings and ends of life. The inverse of care is violence, with the history of fighting and warfare written to some extent on the human skeleton, analyses of which can inform on the prevalence of violence and the changing ways that people have injured and killed each other. We are also interested in the interaction of people and the world around them, which spans the landscape and ecology in which they live, especially the plants and animals, but increasingly also the microbial world of useful bacteria and harmful diseases. Humans are often less central to the world than we have been inclined to think, being part of webs of ecological and physical relations over which they may often have had little control. The world shapes people, but people shape the world. This happens through the major classes of materials and artefacts, from stone to clay to textiles and to metal. Again, the physical properties of changing materials across the globe influences what can be done with them, but also cultural needs, desires, and skills structure how people produce objects in the world. For archaeologists to effectively pursue questions of the past, we need reliable frameworks of dating ranging from organic material to sediments. Understanding the process of preservation and decay sit centrally within our understanding of what is found on different archaeological sites, which limit or enable what we can say about the past from

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one region to another. A single archaeological datum point is rarely of any use or interest, so that understanding trends within our data are crucial, whether these be the distribution of sites across the landscape, the changing heights of human populations, or variability within the chemical composition of bronzes over time and space. We are entering a world of big(ger) data so that unless we are able to interrogate and understand large-­scale sets of information, we will miss out on much that twenty-­first-­century archaeology has to offer. All these areas of understanding the human past and the processes of investigation and frameworks of data on which they are based have been transformed by archaeological science in the last 60 years or so. It is now an impossible thought experiment to try and imagine what all the big issues of archaeology would look like without the influence of archaeological science. When considering the human body singly or en masse, or thinking about the material worlds in which people have lived, archaeological science has made a contribution and in a number of areas has created the field. The impact of archaeological genetics has been profound, transformative, and controversial, and the same is starting to be true in the world of proteins and microbes. This volume contains an intelligent and critical introduction to the overall field in a manner which I have found invaluable and I’m sure others will too. Much is made of the difference and indeed antagonism between science, technology, engineering, and mathematics (STEM) and social sciences, humanities, and the arts (SHAPE) disciplines. Archaeology, for all its faults, is perhaps the most successful of all in integrating the two. In the best archaeological work, it is impossible to say where the science stops and the humanities view starts. This volume contains some thought-­provoking discussions of ethics and cultural values, for instance, as well as presenting much clear text on how archaeological science is carried out.

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Foreword: Archaeological Science and the Big Questions

Not everything is wonderful, however, in the world of archaeological science. There can be a tendency to emphasize various forms of physical determinism and to argue on occasions that major changes have discernible physical causes, such as new technology or an epidemic. Physical causes are generally nuanced by cultural values: reactions to an epidemic amongst people without a germ theory of disease will be very different to that amongst people who do emphasize germs. The funding and prestige of journals for publishing archaeological science are at a different level from most of the archaeology, being more like Big Science than the humanities or social sciences. Big labs are machines for sucking in large amounts of money and producing papers for famous journals, such as Nature and Science, news from which then regularly make their way into television, newspapers, and digital media. This is a heady mix, placing an emphasis on new techniques and discoveries without always critical thought about what such results might mean in human and cultural terms. The editors and contributors to this handbook are aware of such issues, which have the power to deform the whole shape of global archaeology  – the editors’ Introduction picks up some of these questions in a direct and critical manner. My generation of undergraduate students in the 1970s read Brothwell and Higgs as a clear and authoritative

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guide to the broad field of archaeological science. The succession of volumes since provides a unique thread through a fast-­innovating and changing field, as the introduction and the section overviews make clear. This volume is not just the latest in this distinguished lineage but is a clear and authoritative guide to the field of archaeological science, which is now much broader than ever before, sitting right at the centre of the discipline. The introduction, overviews, and individual articles contain a great range and depth of subject matter written by experts in the field. Archaeological science is changing fast and is changing archaeology fast as well. However, the breadth and depth of this book will mean that it stays current for many years to come, allowing the interested reader not just to learn about techniques and approaches but of the strengths and weaknesses of archaeological science as a whole. Debates around the role of archaeological science within the broader discipline will be central for years to come, and the results of archaeological scientists will further transform our understanding of the past. The Handbook of Archaeological Science will be crucial for any non-­ specialist to understand these results, as well as many specialists, in addition to anyone wishing to participate in these broader debates of what archaeology is and what it should become.

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Introduction A.M. Pollard1, Ruth Ann Armitage2, and Cheryl A. Makarewicz3 1

 Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, Oxford, UK  Department of Chemistry, Eastern Michigan University, Ypsilanti, MI, USA 3  Institute of Prehistoric and Protohistoric Archaeology, Christian-­Albrechts-­Universität zu Kiel, Kiel, Germany 2

It is now more than 20 years since the publication of the 2001 edition of Brothwell and Pollard’s Handbook of Archaeological Sciences (Brothwell and Pollard  2001), which in turn drew its inspiration and structure from Brothwell and Higgs’ volume Science in Archaeology, first published in 1963 with a second edition in 1969 (Brothwell and Higgs 1963, 1969). Much has changed since 2001, and so, when the time came to update the Handbook, we took what seemed to be the obvious decision – rather than simply amending the existing chapters to reflect recent work, it would be much better to commission a completely new set of chapters, often by inviting new authors to write fresh contributions. Hindsight might suggest that this was completely insane, since shortly after the initial plans were laid, the world was hit by a pandemic that disrupted most people’s work and put back the proposed timetable by two years. Nonetheless, what is produced here represents an attempt to review the current state of archaeological science. The aim is to provide a single source that covers most topics of interest to archaeological scientists at approximately the final year undergraduate/first-­ year graduate level. New graduate students can hopefully use one or two chapters as a concise introduction to their chosen graduate study, but we also hope that many readers will browse more widely since one of the striking features is how the same issues crop up in different guises in different areas of application, offering the possibility for creative cross-­ disciplinary thinking. We have retained (approximately) the structure of the 2001 volume, although it proved impossible to commission some chapters, but thankfully other authors were able to extend their chapters to cover some of the inevitable gaps. In editing the volume, it is noticeable how two processes

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have been at work over the last 20 years – one is a broadening of the scope of particular fields of application, and another is the increasing convergence between areas of application. An example of the former is the extension of the interpretation of environmental parameters away from local syntheses to much broader hemispherical networks. In terms of the latter, in 2001 we were just about coming to grips with the implications of the survival of proteins in archaeological material and beginning to be able to rely on the genetic data extracted from ancient tissue, although at the time, we were reassured that there had been no genetic exchange between Neanderthal and Homo sapiens  – a point which was queried in the introduction to the section on biomolecular archaeology in the 2001 Handbook (Pollard  2001, p.  297). Activity in these and related areas has accelerated remarkably over the intervening 20 years, and we are now learning to use terms such as proteomics and metabolomics, largely driven by technical developments external to archaeology but finding important applications within our subject area. Similarly, the analysis of inorganic materials has benefitted from external technological developments such as the improvements in mass spectrometry and analytical science, allowing more data to be obtained from ever smaller samples, or in some circumstances completely non-­destructively. Whilst this allows access to data that was almost inconceivable 20 or 30 years ago (although many would point out that neutron activation analysis had similar detection levels for a broad sweep of elements but from larger samples), such capability comes at a cost. It would be extremely interesting to discuss modern analytical chemistry applied to archaeological materials with some of the giants of archaeological chemistry from the middle of the twentieth century, such as

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Introduction

Earle Caley. In his analysis of some Chinese bronzes, for example, he observed that the averaged totals of duplicate analyses combining gravimetric and spectrographic analyses for such alloys was ‘satisfactory for X17b, F130A, and X61a, less so for X67, X71a, and X70, and much less so for X68’ (Caley et al. 1979, p. 187). When checking these totals, ‘satisfactory’ was applied to totals of 99.96, 99.92, and 99.85%; ‘less so’ related to 99.65, 99.65, and 99.63%, and ‘much less so’ to 99.3%. Moreover, he observed that ‘(t)he replicate determinations of copper, tin, and lead in X201 and the duplicate determinations of copper and lead in X204 are in poor agreement’ (Caley et al. 1979, p. 188). The figures to which he refers in X201 are 46.81, 47.2, 47.6, 47.65% for copper, 3.17, 3.03, 2.00, 3.05% tin, and 45.62, 45.66, 46.11, 46.24% lead. In X204, they are 58.24 and 58.80% for copper and 32.34 and 31.32% for lead. He attributes this ‘poor agreement’ to sample inhomogeneity. These comments should prompt several questions in the mind of the users of modern analyses of archaeological material – rarely are duplicate analyses carried out (or if they are done, they are not usually reported); many instrumental analytical techniques do not allow analytical totals to be calculated i­ndependently (or if they are reported, they are usually normalized by the calibration programme so that they are not an independent indicator of analytical quality), and the drive for smaller and smaller samples exacerbates the possibilities of large deviations from the bulk analysis. With a few notable exceptions, it is possible to conclude that analytical standards are in danger of falling. There have, however, been major advances in the analyses of inorganic archaeological materials, but more often in the better articulation of the question addressed to the major concerns of archaeologists. During the ‘golden age’ of inorganic analysis in archaeology (Pollard and Heron 1996, pp. 342–344) – broadly speaking, the middle and second half of the twentieth century, at a time when instrumental methods of analysis (firstly optical emission and latterly neutron activation) allowed large programmes of chemical analysis to be undertaken  – there was widespread enthusiasm for incorporating analytical data on provenance into the ‘New Archaeology’ (later termed ‘Processual Archaeology’: Trigger (2006)). This fitted the general agenda of applying ‘systems theory’ and more ‘scientific rigour’ to research in the social sciences and humanities. Such enthusiasm gradually diminished, however, not only as complications and uncertainties emerged, which rendered the outcomes of such studies either indeterminate or contested, or both, but also because it became increasingly clear that such approaches could not capture completely the behaviour of human beings. This decline in interest in inorganic materials analysis coincided with

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the  rise of bioarchaeology at the end of the twentieth century– initially stable isotopes and then genetics. At one point, it looked as if the days of inorganic materials science in archaeology were numbered  – expensive and destructive and unable to answer any questions that archaeologists were actually interested in – in contrast to the results of the rise of the ‘biomolecular century’ (Pollard  2001), given direct data on human diet, mobility and relationships. This has turned around completely in the last 20 years, with materials science now seen as a major focus in answering some of the big questions in archaeology, such as the origins of social inequality, the nature of technological change, and more generally the complex and changing relationship between humans and their environment (Pollard and Gosden 2023). We may therefore continue to expect further growth in the sciences as applied to archaeology, perhaps most obviously at the interfaces between different disciplines as captured in terms such as proteomics or metabolomics, but also, for example, in the investigation of the role of microbial communities in the corrosion of metal artefacts. This means we can look forward to a long and continuing relationship between the natural sciences and archaeology, which began in the late eighteenth century with the first chemical analyses of archaeological bronzes by the then brand-­new method of gravimetric analysis (Pollard  2018). Inevitably, some of this development will be driven by technological change in instrumental capability external to archaeology, but, hopefully, much of it will be a consequence of an ever-­growing appreciation of the needs of archaeology and the capabilities of science. Perhaps this will lead to ‘better methods applied to better questions’, but we must recall that science itself is a process, not simply a body of knowledge or practice, and is inherently an iterative (and a Bayesian) process  – new information casts new light on current understandings, leading to the necessity for these understandings to be revisited and re-­evaluated. To some, this seems an admission of weakness  – why do we need to ask these questions again, since we have already answered them? – but to others, it is a sign of maturity and vitality. It would not be surprising if, armed with a battery of powerful analytical and interpretational technologies, plus the hindsight provided by previous research endeavours, future archaeological scientists will return to those questions first posed by the true pioneers of  archaeological science in the eighteenth and early ­nineteenth centuries. For example, one is reminded of the work of René Antoine Ferchault de Réaumur (1683–1757), who, amongst his many papers, published several works on  the origins and technologies of steel and porcelain (de Réaumur 1725, 1727, 1729). These are still active areas of research.

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Introduction

Finally, in contemplating the future of Archaeological Science, we might even consider a situation where the term ‘Archaeological Science’ becomes redundant – not because it is irrelevant, but because it has become ‘mainstreamed’. As noted in the tribute to Don Brothwell, Don (amongst many others) was prominent in the promotion of scientific disciplines within archaeology in the 1960s, resulting in the growing specializations first outlined in Science in Archaeology. This has had a profound impact on the practice, nature, and funding of archaeology across the world. However, archaeology is a discipline which draws on all aspects of human knowledge – from art history and astronomy through engineering and medicine to zoology (Pollard  1995). The somewhat artificial (and certainly regrettable) tendency to split science from humanities in academia is undesirable and untenable in archaeology. Many of the flaws of archaeological science in the past

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are  attributable to a lack of meaningful and mutually respective dialogue between ‘scientists’ and ‘archaeologists’. Better, perhaps, to think of ‘archaeological science’ as being an aspect of archaeology, equal in contribution to those of historians, linguists, excavators and finds specialists, etc., but one which is based (conceptually, at least) in a laboratory rather than the field or museum setting. Those who carry out or contribute to such endeavours might better be regarded as ‘laboratory-­based archaeologists’ rather than ‘archaeological scientists’. The editors would like to thank profusely the many contributors to this book – some submitted their chapters to the original timetable and have waited patiently for publication. Others were asked to provide something at the last minute and managed to do so. We are grateful to you all! We also acknowledge the patience of the publishers, who gave us the space and time to inch towards this publication.

­References Brothwell, D. and Higgs, E. (ed.) (1963). Science in Archaeology. London: Thames and Hudson. Brothwell, D. and Higgs, E. (ed.) (1969). Science in Archaeology, 2e. Thames and Hudson: London. Brothwell, D. and Pollard, A.M. (ed.) (2001). Handbook of Archaeological Sciences. Chichester: Wiley. Caley, E.R., Chang, I.S.M., and Woods, N.P. (1979). Gravimetric and spectrographic analysis of some ancient Chinese copper alloys. Ars Orientalis 11: 183–193. de Réaumur, R.-­A.F. (1725). Principes de l’art de faire le Fer Blanc. Histoire de l’Académie Royale des Sciences 1725: 102–129. de Réaumur, R.-­A.F. (1727). Idée générale des differentes maniéres don’t on put faire la Porcelaine; et quelles sont les véritables matiéres de celle de la Chine. Histoire de L’Academie Royale des Sciences 1727: 185–203. de Réaumur, R.-­A.F. (1729). Second mémoire sur la Porcelaine; ou suite des principes qui doivent conduire

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dans la composition des Porcelaines de différents genres. Histoire de L’Academie Royale des Sciences 1729: 325–344. Pollard, A.M. (1995). Why teach Heisenberg to archaeologists? Antiquity 69: 242–247. Pollard, A.M. (2001). Archaeological science in the biomolecular century. In: Handbook of Archaeological Science (ed. D. Brothwell and A.M. Pollard), 295–299. Wiley: Chichester. Pollard, A.M. (2018). Johann Christian Wiegleb and the first published chemical analyses of archaeological bronzes. Journal of the Historical Metallurgy Society 21: 48–54. Pollard, A.M. and Gosden, C. (2023). An Archaeological Perspective on the History of Technology. New York: CUP Elements. Pollard, A.M. and Heron, C. (1996). Archaeological Chemistry. Cambridge: Royal Society of Chemistry 3rd revised edn. 2017. Trigger, B. (2006). A History of Archaeological Thought, 2e. Cambridge University Press: Cambridge.

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Don Brothwell – An Appreciation Terry O’Connor Department of Archaeology, University of York, York, UK

Don Brothwell was a meticulous researcher and inspiring teacher, at times both outspoken and gently humane, encouraging and infuriating, a good friend to many of us, and a key figure in the development of archaeological ­science. As co-­editor with Eric Higgs of the first compilation of research in the field (Brothwell and Higgs  1963), Don helped to bring together what was at that time a rather tenuous, dispersed discipline undertaken ‘on the side’ by investigators in other subject areas. By the time that Don and Mark Pollard were assembling the first edition of this Handbook (Brothwell and Pollard 2001), that was no longer the case. Although contributions to archaeological science came, and continue to come, from many directions, the subject itself now had a clear identity and a substantial research population. Not all of that can be attributed to Don, obviously, but he was certainly a key figure in bringing it about. As well as the two compilation volumes, and perhaps more important than either, was his role in launching the Journal of Archaeological Science in 1974. With Don and Geoffrey Dimbleby as editors and a diverse and international editorial board, JAS provided for the first time a single place of publication through which the whole of archaeological science could define itself and communicate its research. This is not the place for a detailed biographical sketch. Don completed a memoir shortly before his death that is sub-­titled Reflections on a Life and which is informative without being unduly self-­ justifying (Brothwell  2016). A  few details of his childhood and early life point to the man he became. Don was born in 1933  in Nottingham, United Kingdom, the only child of quite ordinary parents, the sort of ‘common people’ on whose lives much of his later research would focus. He experienced childhood ­illnesses, war-­time air-­raids, seaside holidays, street cricket, and the patchy education offered by local primary and

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secondary schools. Don wrote about his childhood briefly and rather analytically, as if it were not an unhappy time but not ­necessarily recalled with much fondness. However, his interests were already moving across and between the humanities and science. In his youth, Don had a particular talent for art, which led him to exploring the art of other cultures and hence to developing an interest in anthropology. Alongside this interest, he was intrigued by old bones and other archaeological relics that were found along the Trent valley and by what they could indicate about the past. Anthropology and archaeology met at Don’s first excavation, undertaken while he was still at school. Previous work at nearby Breedon-­on-­the-­Hill had shown the presence of a Saxon monastery and its cemetery, parts of which were under threat from quarrying. Don and his friends undertook limited excavation work: it was the digging up of bones that brought him into archaeology. One of the crania showed distinctive characteristics thought to be those of Trisomy 21 (Down Syndrome), and rare morphological variants were to become a particular research interest of Don’s (Brothwell 1960). By the time Don entered University College London as a student of anthropology, the range of his interests was very clear, as was the lack of a specific focus. He took courses with a mix of remarkable academics: Daryll Forde, Gordon Childe, Frederick Zeuner, Lionel Penrose, Nigel Barnicot, and Mary Douglas, with the last of whom he was singularly unimpressed. Don graduated in 1956 and began a Doctorate. That remained uncompleted, however, as he took up the post of Demonstrator in Anthropology at the University of Cambridge. Although Don stayed in the post for the full five years of his appointment, he clearly did not enjoy Cambridge and in his later years would occasionally dissect its strengths and weaknesses and those of ­certain renowned academics. However, it was while at

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Don Brothwell – An Appreciation

Cambridge that Don’s research publications began, with a short paper on leprosy in British archaeological material (Brothwell 1958) and what was for its day a quite innovative paper on the use of non-­metric cranial characters in differentiating human populations (Brothwell  1959). Whatever Don thought of Cambridge in retrospect, he made the most of it. It says a lot about the field of anthropology in Britain at that time that a young man aged 27  with no Doctorate would be invited to take up the post of Head of Anthropology at the British Museum, based in what is now the Natural History Museum. However, in 1961 that was Don’s next career move, his obvious potential having been noticed by Kenneth Oakley. Access to human skeletal collections amassed by the Museum and donated by various medical bodies, together with the academic access that came with the institutional address, really gave Don the opportunity to establish his place in physical and biological anthropology. Within a couple of years, the first edition of Science in Archaeology had appeared, to be followed by the prodigious volume Diseases in Antiquity, co-­ edited with Alvin T. Sandison, who became a regular collaborator and good friend (Brothwell and Sandison  1967). What these two ­volumes show is that Don was not lacking in ambition nor in the necessary perseverance, despite a degree of personal modesty and intellect that seemed to flicker around from topic to topic. He was more capable than most of focussing on a particular objective and quietly working away at it, often in parallel with a dozen other things. Colleagues and students who mistook him for a rather disorganized boffin would be surprised when mention of some specific research topic led to Don opening a box-­file to produce some highly relevant notes and graphs that he had put together perhaps twenty years previously. Not only did he remember having done the work, he knew where to find the notes! Other publications during his British Museum years encompassed dental anthropology (Brothwell 1963), the potential of scanning electron microscopy (Brothwell 1969), and the detection of ancient air pollution (Brothwell et  al.  1969). A  more public-­ oriented volume of note was Food in Antiquity, co-­authored with Pat, the first Mrs Brothwell (Brothwell and Brothwell 1969). In 1974, the eminent zooarchaeologist Ian Cornwall retired from his post at the Institute of Archaeology, London, and Don was appointed as Senior Lecturer. He promptly set about expanding his osteological knowledge and research into other vertebrates and began to develop the discursive teaching style that was to inspire, delight, and baffle students in years to come. As one of those students, I recall that one knew where a seminar or practical would begin but never quite knew where it might end, only that the journey would be fascinating. As an

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example, one afternoon Don had taken a group of us to a young Chris Stringer’s office at the British Museum (Natural History) as it then was just as a new delivery of hominin casts had arrived. Out of the box came casts of the Omo I and II crania and what followed was an impromptu, a capella tutorial from Don on the early emergence of Homo sapiens in Africa, almost a decade before Out of Africa became a widely discussed model. Why were we there in the first place? It no longer mattered. Don’s published research during his years at the Institute of Archaeology ranged very widely. The prehistory of treponemal diseases in the Americas and Eurasia became a subject to which Don returned at intervals (Brothwell  1976,  1981a,  2005), as was the fascinating ­subject of bog bodies (Brothwell  1996). Other species were reviewed and investigated, notably dogs (Burleigh and Brothwell  1978; Brothwell et  al.  1979), mice (Brothwell  1981b), and one remarkable paper on guinea pigs that seems almost flippant but actually raises some fundamental questions about the whole process of animal domestication (Brothwell 1983). He supervised a number of PhD students, for whom it was probably a common experience that meetings were difficult to arrange and subject to last-­minute postponement, but were very helpful and constructive even if, as on one occasion, they were held in the café at Swindon station. By now, archaeological science was using a wider range of imaging and analytical equipment, and Don was enthusiastic about the application of whatever tools were available. He encouraged the investigation of dental calculus as a source of dietary evidence (Dobney and Brothwell (1988); see Chapter 28) and would have been delighted to have seen the range of biomolecular and microscopic studies that are now applied to that rather mundane material (Radini et al. 2017; Brealey et al. 2020). Higher Education was changing, however, and Don found himself out of harmony with the new trends and with the directions that the Institute was taking. There are hints in his published work that the state of humanity as a whole was of deep concern to him, leading him to write highly philosophical papers that seem very different to most of his research but which actually reflect a deep-­ seated humanism (Brothwell 1987, 1998). Early retirement began to look like a good option by 1993, then the University of York offered Don a Chair in Human Palaeoecology and the opportunity to refresh his research and teaching at a very different institution. Although York at that time had no archaeological science platform on which to build, Don settled in and made a niche for himself, extending his academic career for another six years. He became particularly involved with studies of mummified human remains, including some celebrated Egyptian examples. Studies of mummies from Yemen involved quite arduous fieldwork

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Don Brothwell – An Appreciation

for a man of mature years (Usai et al. 2010) and Don made a couple of trips to Iran to study the fourth century bce bodies from the Chehr Abad salt mine (Pollard et al. 2008). The technology of mummy studies had moved on considerably since Don’s work with Sandison in the 1960s and the analytical work could have become an end in itself. Don’s important role in those projects was to keep the research grounded in the ancient human beings themselves, whatever new investigative techniques were applied. In 1999, Don retired, though he continued to meet with postgraduate students and to give some undergraduate lectures at York and very welcome support to his successor, and to contribute to teaching elsewhere. The first few years following retirement saw a number of papers published, as diverse as usual, then gradually fewer as declining health and happy grandchildren intervened. Conversations with Don during his retirement years often turned to his concern to understand the connection between consciousness and mind, and to find evidence-­based ways to gain some indication of the mindsets of people in the past. He was acutely aware that the archaeological record is created through the actions of people with their view of reality and interpreted by archaeologists with our view. How far apart are those different views? To what extent, to use one of Don’s favourite phrases, is the modern human mind pathological, predisposed towards violence? There were strong Quaker influences in Don’s childhood and those influences re-­emerged quite strongly in his later years, although he was never religious or a person of faith. Don died in 2016, aged 83. The human mind, however we imagine it, is adept at seeing patterns where an objective analysis might say none exists, whether that manifests as the tendency to see faces in clouds or to argue for significant patterns in random clouds of data. Finding a pattern in Don Brothwell’s diverse, eclectic research output runs just such a risk. One  theme that can be discerned is a strong interest in morphometric variation. What does it mean if a sample of bones from one site show statistically significant differences in size and shape from those at another? That deceptively simple question lay behind Don’s incomplete PhD research into variation in earlier British population samples and was revisited in one of his last papers (Brothwell 2014). When is that variation of phylogenetic significance and when is it essentially phenotypic, indicating that one population underwent quite different life experiences to the other? Answering that question might begin with rigorous statistics, such as Don learned from Penrose and that he insisted his students should learn to use, and perhaps lead towards arguing for differences of status, for restricted growth through chronic inanition or specific nutrient deficiencies. In earlier hominin samples, how much inter-­ sample difference do we need to see to attribute it to

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speciation? All of this came together shortly after Don retired with the discovery of the Liang Bua hominin remains on Flores (Morwood et al. 2004). Interest focussed, as it always does, on the most complete cranium, LB1, and its highly distinctive craniofacial morphology. The Liang Bua research team argued for speciation, that LB1 represented a previously-­unknown hominin taxon. Many others, perhaps concerned by the Late Pleistocene dates for the specimens, tried to make LB1 a morphologically deviant Homo sapiens (Henneberg and Thorne 2004). Don argued that the latter view deserved to be taken seriously, in particular the possibility that local chronic iodine deficiency could have led to the restricted growth shown by the LB material (Obendorf et  al.  2008). It was typical of Don to amass a considerable body of research material, to give the ‘cretinism’ hypothesis every opportunity to be supported, even as informed opinion was moving more and more towards accepting the LB hominins as a new species. In the end, Don’s persistence in testing every possible explanation probably led him astray with regard to LB1. In contrast, that persistence and his wide knowledge of human cranial variability were key to understanding the famous Kow Swamp Late Pleistocene human remains from Southeastern Australia. Crania in the Kow Swamp assemblage have a very distinctive profile, with strong brow ridges and a low frontal profile. The site excavator Allan Thorne argued that the crania showed Homo erectus traits, in effect proposing a local derivation of H. sapiens from Eastern H. erectus populations (Thorne and Wolpoff 1981). This was controversial, in part for promoting a multiregional model when much of the debate was heading towards Out of Africa, and more so because of the implications for the status of modern Australian Aborigines. Don disagreed with Thorne, pointing out that the crania showed many of the features of artificial modification, for example through binding the head in children in order to produce a distinctive adult head shape (Brothwell 1975). Thorne disagreed in turn and quite forcefully, but Don stuck to his view. Years later, with more examples of cranial modification available from the wider Australasian region, meticulous morphometric work by Arthur Durbrand and others showed that cranial modification was much the more likely explanation for the Kow Swamp crania (Durband  2008). Though persistence in research can sometimes be difficult to distinguish from obstinacy, it was vindicated on this occasion. There was unquestionably a touch of obstinacy about Don Brothwell. He would keep faith with a favourite ­theory despite contrary evidence, surgically pointing out the flaws and gaps in any counter-­argument. He wanted nothing to do with email, even when it became the principal means of communication among academics, and found the internet

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to be alarming and depressing in equal measure. Don’s ­university career was delayed by a spell in prison when he refused to co-­operate with the National Service call-­up, and he stubbornly took on the Catholic Church over the education of his older children. Those were matters of principle, and while Don could be happily pragmatic over many things, militarism and religion were to be taken seriously. On the other hand, it meant that he stuck by people, for example supporting that most eccentric of archaeological scientists Leo Biek, whom many colleagues were too ready to write off. There was empathy, too. Don would speak with real regret of friends and colleagues who turned to drink or suicide. He was wrong about emails and LB1 but right about much else.

In all, Don Brothwell’s contribution to archaeological science over five decades was substantial and diverse. It consists in part of his research papers, often very particular fine-­grained studies of some detailed topic, of the compilation volumes that he co-­edited in order to bring together in one place a summary of the current state of a research field and of the careers of former students whom he bewildered and inspired. Somewhere between Socratic and anarchic, his teaching methods would not be acceptable today, and the eclectic breadth of his research would be regarded askance. That is academia’s loss. Inter-­disciplinary subjects such as archaeological science need polymaths who can make connections between diverse specialisms, and Don Brothwell was one of the best.

­References Brealey, J.C., Leitão, H.G., van der Valk, T. et al. (2020). Dental calculus as a tool to study the evolution of the mammalian oral microbiome. Molecular Biology and Evolution 37: 3003–3022. Brothwell, D.R. (1958). Evidence of leprosy in British archaeological material. Medical History 2: 287–291. Brothwell, D.R. (1959). The use of non-­metrical characters of the skull in differentiating populations. Bericht der Deutschen Gesellschaft für Anthropologie in Kiel 6: 103–109. Brothwell, D. (1960). A possible case of mongolism in a Saxon population. Annals of Human Genetics 24: 141–150. Brothwell, D.R. (ed.) (1963). Dental Anthropology. London: Pergamon. Brothwell, D. (1969). The study of archaeological materials by means at the scanning electron microscope: an important new field. In: Science in Archaeology: A Survey of Progress and Research (ed. D.R. Brothwell and E.S. Higgs), 564–566. Thames and Hudson: London. Brothwell, D. (1975). Possible evidence of a cultural practice affecting head growth in some Late Pleistocene East Asian and Australasian populations. Journal of Archaeological Science 2: 75–77. Brothwell, D.R. (1976). Further evidence of treponematosis in a pre-­European population from Oceania. Bulletin of the History of Medicine 50: 435–442. Brothwell, D. (1981a). Microevolutionary change in the human pathogenic treponemes: an alternative hypothesis. International Journal of Systematic and Evolutionary Microbiology 31: 82–87. Brothwell, D.R. (1981b). The Pleistocene and Holocene archaeology of the house mouse and relate species. In: Biology of the House Mouse (ed. R.J. Berry), 1–13. Academic Press: London.

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Brothwell, D. (1983). Why on Earth the guinea-­pig? The problem of restricted mammal exploitation in the new world. In: Site, Environment and Economy (ed. B. Proudfoot), 115–119. British Archaeological Reports: Oxford. Brothwell, D. (1987). Biophilosophical aspects of archaeology. Bulletin of the Institute of Archaeology, University of London 24: 177–190. Brothwell, D. (1996). European bog bodies: current state of research and preservation. In: Human Mummies (ed. K. Spindler, H. Wilfing, D. Nedden and H. Nothdurfer), 161–172. Springer: Vienna. Brothwell, D. (1998). Stress as an aspect of environmental studies. Environmental Archaeology 2: 7–13. Brothwell, D.R. (2005). North American treponematosis against the bigger world picture. In: The Myth of Syphilis: The Natural History of Treponematosis in North America (ed. M. Powell and D. Cook), 480–496. University Press of Florida: Gainesville. Brothwell, D. (2014). The biology of early British populations. In: Archaeological Human Remains (ed. B. O’Donnabhain and M. Lozada), 65–84. Springer: Heidelberg. Brothwell, D.R. (2016). A Faith in Archaeological Science: Reflections on a Life. Oxford: Archaeopress. Brothwell, D. and Brothwell, P. (1969). Food in Antiquity. London: Thames and Hudson. Brothwell, D.R. and Higgs, E.S. (1963). Science in Archaeology, 2e. London: Thames and Hudson. Brothwell, D.R. and Pollard, A.M. (ed.) (2001). Handbook of Archaeological Sciences. Chichester: Wiley. Brothwell, D.R. and Sandison, A.T. (ed.) (1967). Diseases in Antiquity. CC Thomas: Springfield. Brothwell, D.R., Sandison, A.T., and Gray, P.H.K. (1969). Human biological observations on a Guanche mummy

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with anthracosis. American Journal of Physical Anthropology 30: 333–347. Brothwell, D., Malaga, A., and Burleigh, R. (1979). Studies on Amerindian dogs, 2: variation in early Peruvian dogs. Journal of Archaeological Science 6: 139–161. Burleigh, R. and Brothwell, D. (1978). Studies on Amerindian dogs, 1: carbon isotopes in relation to maize in the diet of domestic dogs from Early Peru and Ecuador. Journal of Archaeological Science 5: 355–362. Dobney, K. and Brothwell, D. (1988). A scanning electron microscope study of archaeological dental calculus. In: Scanning Electron Microscopy in Archaeology (ed. S. Olsen), 372–385. British Archaeological Reports: Oxford. Durband, A.C. (2008). Artificial cranial deformation in Kow Swamp 1 and 5. Homo 59: 261–269. Henneberg, M. and Thorne, A. (2004). Flores human may be pathological Homo sapiens. Before Farming 4: 2–4. Morwood, M.J., Soejono, R.P., Roberts, R.G. et al. (2004). Archaeology and age of a new hominin from Flores in Eastern Indonesia. Nature 431: 1087–1091.

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Obendorf, P.J., Oxnard, C.E., and Kefford, B.J. (2008). Are the small human-­like fossils found on Flores human endemic cretins? Proceedings of the Royal Society B: Biological Sciences 275: 1287–1296. Pollard, A.M., Brothwell, D.R., Aali, A. et al. (2008). Below the salt: a preliminary study of the dating and biology of five salt-­preserved bodies from Zanjan Province, Iran. Iran 46: 135–150. Radini, A., Nikita, E., Buckley, S. et al. (2017). Beyond food: the multiple pathways for inclusion of materials into ancient dental calculus. Yearbook of Physical Anthropology 162 (S63): 71–83. Thorne, A.G. and Wolpoff, M.H. (1981). Regional continuity in Australasian Pleistocene hominid evolution. American Journal of Physical Anthropology 55: 337–349. Usai, M.R., Brothwell, D., Buckley, S. et al. (2010). Micromorphology of two prehistoric ritual burials from Yemen, and considerations on methodological aspects of sampling the burial matrix-­work in progress. EGU General Assembly Conference Abstracts 2010, 3715.

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1

Section 1 Science-­based Dating in Archaeology Christopher Bronk Ramsey

Archaeology as a discipline is focused on the study of human activity through the physical evidence which survives to be analyzed. Increasingly this includes not only evidence from archaeological sites per se but also evidence of human activity seen in a wide range of environmental records from ice cores to lake sediments. The recovery of material from these different archives directly provides location information and even, through the application of the principles of stratigraphy, some information on relative age. However, it is only really direct dating techniques which allow us to determine rates of change and to understand the underlying processes on a broad scale. The precision we require of our dating methods depends on the kinds of questions we wish to ask: for some questions, we are satisfied with ages in thousands of years, but to address others, we may require dating precision at a whole range of scales right down to sub-­annual. Science-­based dating in archaeology, therefore, strictly includes both methods which can be used to directly date material from archaeological sites and the panoply of methods which are applied to environmental records more generally, what we can broadly refer to as the Quaternary geological framework (Chapter 1). One of the most major advances in the last decade or so has been the integration of these frameworks with archaeological evidence through both high-­precision direct dating and methods of correlation such as tephrochronology (Chapter  8). Another key change has been ever greater emphasis on the interconnections between human activity and the environment with the associated debate over the definition of the Anthropocene (Chapter 1).

­Principles Common to All Dating Techniques All direct dating methods share some core features which it is important to understand. Perhaps the best place to start is the materials to which they can be applied. For example, the main reason that radiocarbon dating (Chapter 2) is far more commonly used on archaeological sites than are the argon techniques (K-­Ar and 39Ar/40Ar, see Chapter  8) is that the former can be applied to a wide range of biological material and the latter only to high-­potassium mineral crystals from volcanic eruptions. The constraint of what sample types can be found on archaeological sites is one of the key determinants on what methods can be applied. This often requires compromises to be made between the samples that most directly relate to the archaeological question and the materials that are susceptible to the most reliable techniques. Ideally, more than one technique will be applied, especially in cases which are controversial, since no dating method is perfect. Another characteristic of all dating techniques is the ‘dated event’. This is the event that in a physical sense is being measured by the method and which may differ from the archaeological event of interest. An obvious example would be dendrochronology which dates the growth of rings in the tree, perhaps including the final ring, but not the use of the wood in a structure of an artefact (Chapter 3). Many misinterpretations of dating evidence come from failing to understand the dated event properly or cases where the event is more of an ongoing process, such as the uptake of uranium into bone (Pike and Pettitt 2003). In order to have a well-­defined dated event, we usually need a closed system.

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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Science-­based Dating in Archaeology

System closure is a key feature of methods such as uranium series dating (Chapter 5) and the more recent applications of amino acid dating (Chapter 7); it also underpins the drive to more specific pre-­treatment methods of radiocarbon dating (Chapter  2), which aim to either select particular closed-­ system compounds or to otherwise remove material which is not original to the sample (Brown et  al.  1988; Bird et al. 1999; Stott et al. 2001; Devièse et al. 2017). In addition to an event which starts the process, any direct dating technique requires something which changes at a defined rate. There are essentially three distinct types of processes used: the Earth’s orbit (astronomical clocks), radioactive decay, and chemical change. The first two of  these are the most secure and generally underly all other  methods, including those that rely on correlations. Fundamentally this is because both astronomical orbits and radioactive decay are highly predictable, whereas chemical change is susceptible to other confounding variables such as temperature, and correlative methods require additional underlying assumptions. The final important characteristics of dating methods are their age range and their precision. For example, the restriction of radiocarbon dating (Chapter  2) to the last 55 ka is a key limiting factor in its use for studying human evolution. The limited precision of many of the techniques in use also prevents their use for addressing potentially interesting archaeological problems and is a reason why increased precision is always an important focus for developments. Over the last decade, precisions in many dating methods have improved significantly; some of this is new instrumentation as for radiocarbon dating (Chapter  2), argon dating methods (Chapter 8) and as seen in applications of uranium series dating of speleothems (for example, Cheng et al. (2018); see Chapter 5). In other cases, even more dramatic improvements in precision have been possible through new approaches: in particular radiocarbon dating (Chapter  2), which normally has a resolution of about a century after calibration, can have this improved by about an order of magnitude by the use of wiggle-­ matching of tree ring sequences (Chapter  3), and to an annual resolution where rapid production of atmospheric radiocarbon (Miyake events) can be picked up (Miyake et al. 2012, 2013).

­Astronomical Clocks Our very definition of time is fundamentally astronomical, and some of the dating techniques make direct use of characteristics of the Earth’s rotation and orbit around the sun. From a dating perspective, this unfortunately only works on fairly widely spaced scales. Apart from the daily cycle,

which is only relevant normally where we have calendar dates, the key cycles are the annual seasonal cycle and the 10–100 ka cycles in eccentricity, obliquity and precession, which all help drive the long-­term climate cycles (Chapter 1; Croll (1890), Milankovitch (1941)). The annual seasonal cycle is essentially what we use in dendrochronology (Chapter  3) and also in the ice-­core counting and lake-­varve sequences, which feed into the Quaternary geological framework (Chapter  1; see also Chapter 9). This potentially gives these methods the ability to date to a sub-­annual resolution (Rasmussen et al. 2014). The orbital timescales are also key to the much longer-­ term geological timescales used in the Quaternary including the composite marine records (Raymo and Nisancioglu 2003). From an archaeological perspective, they provide the timescale for the environmental context for human evolution. They also indirectly provide the orbitally tuned calibration for the Ar–Ar dating method (Kuiper et al. 2004). Perhaps one of the key underlying issues in chronology is that there is no well-­defined astronomical cyclicity between the annual cycle and the precession of the orbit, meaning that for dating at the decadal, centennial, and millennial scale, we have to turn to other methods.

­Radioactive Decay Rates The fundamental dating methods not reliant on astronomical clocks make use of the insensitivity of the rate of radioactive decay to temperature and chemical context. This constancy is made use of in two distinct ways: the first by looking at the decay series themselves, and the second is by measuring the effect of radiation on mineral crystals. The main direct decay chain methods used in archaeology are the argon dating techniques (K-­Ar and 39Ar/40Ar, see Chapter 8) or uranium series (for example, on speleothems records; see Chapters  1 and  5). Radiocarbon (Chapter 2) is a special case in that we only measure the parent isotope in the chain, and for dating, we must calibrate which effectively means that it is a correlation technique. Uranium series also has been applied to open systems such as bone, but here there are chemical changes taking place too, complicating the situation (see Chapter 5, and also, for example Pike and Pettitt (2003), Eggins et al. (2005)) and so could be considered as a chemical change method in combination with isotope decay. The methods which operate on the rate of incidence of radiation include the luminescence and ESR methods collectively referred to as trapped charge dating (Chapter  4) and fission track dating (as applied to volcanic minerals, see Chapter 8). With all these methods, however, although the radioactive decay rates themselves are constant, the

­Interdependenc 

dose experienced by mineral grains is affected by changes in deposition environment geometry chemistry and, perhaps most problematically, water content. For these reasons, precision is often limited to 5–10% (see Chapter  4). For many purposes, however, this is very useful, and the range of materials that can be dated in this way is constantly expanding (see Chapter 4).

­Chemical Change The rate of chemical change can also be used as a dating tool. Indeed, when we consider something to ‘look’ old, what we normally mean is that it shows visible signs of degradation arising from chemical change. The issue is that chemical change is very dependent on external factors, particularly temperature and chemical context. For this reason, only particular systems are suitable for this type of dating, and considerable care is needed in their application. Amino acid dating is a very good example of this. Originally conceived of as a method for dating proteins in general, careful research has shown that when applied to closed systems, it is possible to build aminostratigraphies for different species, which are very robust (see Chapter 7). There is a growing range of biominerals susceptible to this type of analysis with sufficiently different racemization rates that the whole of the quaternary is potentially datable in this way. For these reasons, although there is still a strong dependence on temperature, the power of this method is becoming increasingly apparent. Obsidian hydration dating is also fundamentally concerned with a chemical process of hydration and has some of the same issues as amino acid dating. The exact diffusion mechanism is still an active area of research, and this has been greatly helped by using SIMS to measure diffusion profiles (e.g. Liritzis 2006; Laskaris et al. 2011, 2017). In general, dating of open systems includes an element of chemical change which is why it can be problematic as in the case of uranium series dating of bone (Pike and Pettitt 2003), requiring chemical change to be properly factored into the age calculation (see for example, Eggins et al. (2005)). The chemical change methods in general show that, with careful scientific research and choice of samples, it is possible to extract accurate age information from processes which are not totally constant over time.

­Correlation In addition to the techniques which can be used directly for dating, we have a number of methods which can be used to infer dates by correlation. These methods rely on a number of different mechanisms.

Variation in the Earth’s magnetic field over time, although largely unpredictable leaves detectible traces in a number of different archives. On the very long timescale, we can use global reversals (magnetostratigraphy) and, on  a shorter timescale, more subtle changes. These are ­relevant both for building our geological frameworks (Chapter 1) or for directly dating features in archaeological sites (Chapter 6). The increasing availability of local records of secular variation, and the application of Bayesian methods (Lanos et al. 2005), have increased the applicability of this method. The tephra deposits from volcanic eruptions provide another method to find synchronisms between terrestrial, marine, and ice core records, albeit only sporadically (Chapter  8). Again, the amount of primary work in  this area has greatly expanded its scope over the last decade. Although seen by many as a radiometric method, radiocarbon dating (Chapter  2), with its calibration stage (Reimer et al. 2020), is really a method of correlation: the sample that we date by radiocarbon is dated by association with material giving a similar radiocarbon measurement in independently dated calibration records. On a much more local scale, we use correlation in growth patterns, or  more recently also isotopic signals, for cross-­dating in dendrochronology (Chapter 3). In all these methods, we are making use of signals which are either of geological or atmospheric origin which transcend individual sites and allow us to transfer timescales from one site to another.

­Interdependence The importance of correlation underlines the interdependence of the dating methods available with the purely astronomical and radiometric methods providing the underlying timescale for all the other methods. Radiocarbon ultimately derives its calibrated timescale from a combination of dendrochronology and uranium-­series dating (Reimer et  al. (2020); see Chapters  2,  3, and  5). Archaeomagnetic dating (Chapter 6) relies for its archaeological applications on records of secular variation derived from dendrochronology, luminescence dating, and historical records. Volcanic ash layers used in tephrochronology (Chapter 8) are dated using radiocarbon, argon dating techniques (K–Ar and 39Ar/40Ar), uranium series dating on zircons, and fission track dating. In other cases, the limitations in techniques can be mitigated by using a combination as is frequently the case with ESR and uranium series dating (Chapters 4 and 5). Even where methods do not directly rely on one another, they

3

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Science-­based Dating in Archaeology

are often used to cross-­check each other, for example, luminescence dating (Chapter 4) and radiocarbon (Chapter 2), where their age ranges overlap.

­Integration Given the interdependence of the different dating techniques, considerable effort has been put into the integration of information from multiple dating techniques and other lines of evidence. Progress is particularly evident in the construction of geological chronological frameworks (Chapter 1) aimed at better quantification and understanding of the Earth system. The Antarctic and Arctic ice records have been synchronized using methane synchronization (Köhler  2010) and are used in the construction of our broader geological frameworks (see Chapter  9). Perhaps equally importantly, the relationship between 10Be in the ice cores and 14C in the atmosphere has been used to synchronize those ice core records, so important for understanding climate, with the calibrated radiocarbon timescale (Adolphi and Muscheler 2016; Adolphi et al. 2018), with decadal level precision in the Holocene and Late Glacial periods. The presence of spikes in the production of both isotopes (Miyake et al. 2012, 2013) have further helped refine this to be precise to the year. The radiocarbon calibration curve itself is built up of a very wide range of records integrated through absolute dating and 14C pattern matching (Chapter  2; Reimer et  al. (2020), Heaton et  al. (2021)). Similar efforts have been made for marine records and speleothems (see Chapter 1). Tephra provides another key tool for integrating records  particularly on a regional basis, and this is often done through the use of Bayesian chronological models (Chapters 2 and 59), which allows information from multiple sites to be used to provide indirect dates for eruptions

which cannot be directly dated (Chapter 8). Bayesian analysis can also be applied directly to archaeological chronologies, perhaps most often for radiocarbon (Chapter  2) but with the inclusion of other types of dating information such as dendrochronological dates (Chapter  3) and luminescence (Chapter 4). Bayesian methods are also central now to the application of archaeomagnetic dating (Chapter 6). The real power in these techniques is their flexibility which enables them to include not only direct dating evidence but also constraints from stratigraphy or models of deposition.

­Conclusions There are considerable overlaps between the dating methods used in archaeology and other related fields. This synergy is very helpful for archaeologists, particularly where they wish to understand things within the broader geological framework (Chapter 1); it is also useful on a much more practical level in that much work has been done on, for example, radiocarbon records (Chapter 2) and dendrochronological reference chronologies (Chapter  3) which was primarily intended for understanding palaeoclimate but which archaeologists can use for other purposes. To make best use of all this information though, it is important not to see any of the individual dating techniques as an isolated method to be applied without understanding the relationship between the different methods and timescales for the records which are dated by them. Dating methods have developed a lot in the last decade or two, but much of the improved precision and capability comes at the cost of requiring more care in the selection of samples, the dating itself, and above all in the interpretation of the data. It becomes increasingly important that chronology is seen as an important element within archaeological research.

­References Adolphi, F. and Muscheler, R. (2016). Synchronizing the Greenland ice core and radiocarbon timescales over the Holocene–Bayesian wiggle-­matching of cosmogenic radionuclide records. Climate of the Past 12: 15–30. Adolphi, F., Bronk Ramsey, C., Erhardt, T. et al. (2018). Connecting the Greenland ice-­core and U/Th timescales via cosmogenic radionuclides: testing the synchroneity of Dansgaard–Oeschger events. Climate of the Past 14: 1755–1781. Bird, M.I., Ayliffe, L.K., Fifield, L.K. et al. (1999). Radiocarbon dating of “old” charcoal using a wet

oxidation, stepped-­combustion procedure. Radiocarbon 41: 127–140. Brown, T.A., Nelson, D.E., Vogel, J.S., and Southon, J.R. (1988). Improved collagen extraction by modified Longin method. Radiocarbon 30: 171–177. Cheng, H., Lawrence Edwards, R., Southon, J. et al. (2018). Atmospheric 14C/12C changes during the last glacial period from Hulu Cave. Science 362: 1293–1297. Croll, J. (1890). Climate and Time in Their Geological Relations: A Theory of Secular Changes

 ­Reference

of the Earth’s Climate. New York: Cambridge University Press. Devièse, T., Comeskey, D., McCullagh, J. et al. (2017). New protocol for compound specific radiocarbon analysis of archaeological bones. Rapid Communications in Mass Spectrometry 32: 373–379. Eggins, S.M., Grün, R., McCulloch, M.T. et al. (2005). In situ U-­series dating by laser-­ablation multi-­collector ICPMS: new prospects for Quaternary geochronology. Quaternary Science Reviews 24: 2523–2538. Heaton, T.J., Bard, E., Bronk Ramsey, C. et al. (2021). Radiocarbon: a key tracer for studying Earth’s dynamo, climate system, carbon cycle, and Sun. Science 374: 6568. Köhler, P. (2010). Rapid changes in ice core gas records – part 1: on the accuracy of methane synchronisation of ice cores. Climate of the Past Discussions 6: 1453–1471. Kuiper, K.F., Hilgen, F.J., Steenbrink, J., and Wijbrans, J.R. (2004). 40Ar/39Ar ages of tephras intercalated in astronomically tuned Neogene sedimentary sequences in the Eastern Mediterranean. Earth and Planetary Science Letters 222: 583–597. Lanos, P., Le Goff, M., Kovacheva, M., and Schnepp, E. (2005). Hierarchical modelling of archaeomagnetic data and curve estimation by moving average technique. Geophysical Journal International 160: 440–476. Laskaris, N., Sampson, A., Mavridis, F., and Liritzis, I. (2011). Late Pleistocene/Early Holocene seafaring in the Aegean: new obsidian hydration dates with the SIMS-­SS method. Journal of Archaeological Science 38: 2475–2479. Laskaris, N., Liritzis, I., Bonini, M. et al. (2017). AFM and SIMS surface and cation profile investigation of

archaeological obsidians: new data. Journal of Cultural Heritage 25: 101–112. Liritzis, I. (2006). SIMS-­SS a new obsidian hydration dating method: analysis and theoretical principles. Archaeometry 48: 533–547. Milankovitch, M. (1941). Kanon der Erdbestrahlung und seine Anwendung auf das Eiszeitenproblem. Royal Serbian Academy Special Publication 133. Mihaila Ćurčića: Belgrade. Miyake, F., Nagaya, K., Masuda, K., and Nakamura, T. (2012). A signature of cosmic-­ray increase in AD 774–775 from tree rings in Japan. Nature 486: 240–242. Miyake, F., Masuda, K., and Nakamura, T. (2013). Another rapid event in the carbon-­14 content of tree rings. Nature Communications 4: 1748. Pike, A.W.G. and Pettitt, P.B. (2003). U-­series dating and human evolution. Reviews in Mineralogy and Geochemistry 52: 607–630. Rasmussen, S.O., Bigler, M., Blockley, S.P. et al. (2014). A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-­core records: refining and extending the INTIMATE event stratigraphy. Quaternary Science Reviews 106: 14–28. Raymo, M.E. and Nisancioglu, K.H. (2003). The 41 kyr world: Milankovitch’s other unsolved mystery. Paleoceanography and Paleoclimatology 18: 1011. Reimer, P.J., Austin, W.E.N., Bard, E. et al. (2020). The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0–55 cal kBP). Radiocarbon 62: 725–757.

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1 Quaternary Geochronological Frameworks Christine S. Lane Department of Geography, University of Cambridge, Cambridge, UK

The Quaternary Period, spanning the last 2.588  million years (Ma) (Cohen and Gibbard 2019), is the latest period within the Cenozoic Era (Cohen et al. 2013) and followed the onset of global cooling and Northern Hemisphere glaciations in the latest Pliocene (Lisiecki and Raymo 2007). The Quaternary Period is characterized by glacial to interglacial cycles that oscillate on tens of thousands of year timescales (Figure 1.1) and increase in length and amplitude toward the present. The ice age cycles are controlled by astronomical variables modified by earth-­system feedbacks that together control the distribution of heat around the planet. Evidence for the Quaternary ice age cycles, and for shorter-­term (sub-­orbital, millennial-­scale) climate oscillations, can be found within globally distributed marine and terrestrial archives, underlining the role of global ­teleconnections in the climate system (e.g. Stocker and Johnsen 2003; Markle et al. 2017). Long, dated, and replicated records, such as marine sediment oxygen isotope stacks (e.g. Lisiecki and Raymo  2005), continental loess sequences (Sun et  al.  2006), speleothems (e.g. Cheng et al. 2016), and polar ice cores (e.g. Rasmussen et al. 2014) provide important chronostratigraphic frameworks for defining, correlating, and dating Quaternary successions on a range of timescales. In contrast to regionally defined and diachronous archaeological periods, the chronostratigraphic units of the Geologic Timescale (Figure  1.1) are determined with globally isochronous boundaries. The Quaternary Period thus provides a globally applicable geochronological and climatostratigraphic framework within which the spatial and temporal complexities of hominin behavioural and biological evolution, and of human history, may be contextualized. Climate change is frequently cited as a driving

force in aspects of hominin evolution and human history (e.g. Grove 2015; Potts and Faith 2015; Büntgen et al. 2016; Lupien et al. 2020). However, critically unpicking the relationships between humans and their changing environments demands precise comparative chronologies and robust ­dating frameworks. This chapter aims to introduce Quaternary geochronological frameworks on multiple scales, highlighting those archives and tools that provide chronological frameworks for the integration of palaeoclimate and archaeological datasets. We will consider the drivers, dating and recorders of glacial–interglacial cycles, millennial-­scale climate changes of the Last Glacial Cycle, and the highly-­resolved centennial-­to decadal-­scale variability within the Holocene Epoch.

­The Structure of the Quaternary Definition and subdivision of the Quaternary Period by the International Union for Geological Science’s (IUGS) Commission on Quaternary Stratigraphy (Figure 1.1) relies on the identification and precise dating of global boundary stratotype sections and points (GSSPs), so-­called golden spikes, that represent climatic or environmental transitions widely recognized in geological sequences (Smith et al. 2015; Cohen and Gibbard 2019). The Quaternary Period is subdivided into the Pleistocene (2.588 Ma – 11.7 thousand years [ka] Before Present [BP]) and Holocene Epochs (11.7 ka BP to present), which are each in turn divided into sub-­epochs (Walker et  al.  2009; Gibbard et al. 2010; Cohen and Gibbard 2019). The Early Pleistocene (2.588–~0.773 Ma BP) Earth was characterized by ~41 ka glacial–interglacial cycles (Ruddiman et al. 1986),

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

Quaternary Geochronological Frameworks

(a) 0

1

2

3

Age (ka B2k) 5 6 7

4

8

9

10

11

Holocene

Epochs Sub-epochs

Meghalayan

0

8.236

0.5

Epochs Sub-epochs Late

Northgrippian

Greenlandian 4.25

11.702

Age (Ma BP) 1.5

1.0

2.0

2.5

Pleistocene Middle

Early

0.126

0.773

2.588

(b) Chrons Subchrons

Geomagnetic field direction

Matuyama

Bruhnes

Normal Reversed

(c) July Insolation 65°N

Wm–2

500 460 420 380

Precession

(°)

25.0

0.06 0.03 0.00 –0.03 –0.06

Obliquity

24.0 23.0 22.0

0.06 0.04 0.02 0.00

Eccentricity

Interglacials

(d) 3.0

1

5e

9e

11

7e 7a

3.5

δ18O (‰)

8

13

17

19

31

25

21

27

9a

5a

29

37 35 33

47 43 39 41 45

49 51

53

3 28

4.5 4 2

0

14

8 6

18

10

20

22

75 55 63 67 73 61 57 59 71

500

79

24 26

30

32 34

36

42 44 48 38 40 46 50 52

76 66 72 56 64 70 74 54 58 60 62 78

87 9193 97 95 83 85 89

84 82

88 86

90

94 92 96 98

Glacials

16

12

81

77

80

23

4.0

5.0

15

1000

1500

2000

2500

Age (ka BP)

Figure 1.1  The Quaternary chronostratigraphic record, including key chronological and climate stratigraphies. (a) The subdivision of the Quaternary Period according to the International Union for Geological Science’s (IUGS) Commission on Quaternary Stratigraphy. Source: Adapted from Cohen and Gibbard (2019). (b) The Geomagnetic Polarity Timescale (GPTS). Source: Adapted from Ogg (2012) and Channell et al. (2020). (c) July insolation at 65°N modelled from the orbital precession, obliquity, and eccentricity cycles. Source: Adapted from Hays et al. (1976). (d) The LR04 δ18O benthic marine stack. Source: Adapted from Lisiecki and Raymo (2005), Emiliani (1955), Imbrie et al. (1984), Shackleton et al. (1995).

which transitioned after ~800 ka BP into ~100 ka cycles as glacial stages intensified, and ice sheets expanded into the Middle Pleistocene. The base of the Middle Pleistocene Epoch (~0.773–0.126 Ma BP) has been drawn coincident with the Brunhes–Matuyama magnetic reversal (Suganuma et al. 2015), which provides a globally isochronous horizon

detectable in many marine and continental sequences. The Late Pleistocene (~126–11.7 ka BP) spans only the last interglacial and glacial cycle; terminating at the onset of the Holocene Epoch (Walker et  al.  2009). The Late Pleistocene is well represented in many highly-­resolved extended records, including marine and lake sediment

­Orbital Pacing of the Ice Age Cycle 

sequences, speleothems, and the polar ice cores (e.g. Wang et al. 2008; Capron et al. 2010; Fletcher et al. 2010; Moseley et  al.  2020). Such sequences reveal globally pervasive, although not uniform, millennial-­scale climatic oscillations between cold (stadial) and warm (interstadial) conditions, which form the basis of regional climate-­based event-­ stratigraphic frameworks for correlation and comparison of Late Pleistocene sequences (Feurdean et  al.  2014; Moreno et al. 2014; Rasmussen et al. 2014). A ‘golden spike’ set at 11.7 ka B2k (years before 2000 ce) in the NGRIP ice core (Walker et al. 2009) marks the abrupt onset of the Holocene Epoch  – our present interglacial (Figure 1.1). The Holocene is divided into three sub-­epochs, which again mark global climatic variations and are ­pin-­pointed in ice core and speleothem records: the Early Holocene (Greenlandian Age) lasted from 11 702 to 8226 years (a) B2k, the Middle Holocene (Northgrippian Age) from 8236 to 4250 a B2k, and the Late Holocene (Meghalayan Age) began 4250 a B2k and continues to the present day (Walker et  al.  2018). Climate variability during the Holocene was relatively low in amplitude with insolation-­ driven warming leading to a regionally diachronous thermal maxima in the Middle Holocene, followed by cooling until the rise of anthropogenic warming in the last 150 years (Marcott et  al.  2013; Kaufman et  al.  2020). Global proxy records also evidence abrupt events that punctuated the otherwise smooth Holocene climate curve, and it is these that form the subdivision boundaries (Walker et  al.  2018). The 8.2 ka BP cooling event, which marks the Late to Middle Holocene transition, is widely attributed to a glacial freshwater outburst in the North Atlantic (Barber et al. 1999; Rohling and Pälike  2005; Thomas et  al.  2007; Cheng et al. 2009a; Matero et al. 2017). The 4.2 ka BP event, which marks the Middle to Late Holocene transition, saw the reorganization of atmospheric and oceanic circulation ­patterns, marked in many mid to low latitude records as a multi-­centennial aridity event (Bar-­Matthews et  al.  1999; Cullen et  al.  2000; Berkelhammer et  al.  2012; Railsback et al. 2018). The quality and resolution of proxies used to reconstruct Late Pleistocene and Holocene environments (PAGES 2k Consortium et al. 2013; Kaufman et al. 2020) means that the changing climatic and environmental ­conditions of the Holocene, more than any earlier interval, can be succinctly aligned to the last ~12 ka of human (pre) history (e.g. Büntgen et  al.  2016; Carolin et  al.  2019; Xu et al. 2019). Moving through the Holocene toward the present, it becomes increasingly possible to use chronological tools to test hypotheses about climatic drivers of increasingly complex human behaviour. Since the coining of the term Anthropocene by Crutzen and Stoermer (2000), debate has surrounded the definition of a new geological Epoch succeeding the Holocene, which

recognizes the impact of humankind on the Earth’s ­geological formations and climate record. Crutzen (2002) identifies the beginning of the industrial revolution  – as marked by James Watts’ 1784  invention of the steam engine  – as the point at which humans’ impacts on the global environment escalated. The IUGS Anthropocene Working Group places the Anthropocene Epoch GSSP in the mid-­twentieth century, in line with the so-­called Great Acceleration (Waters et al. 2018); however, earlier boundaries have been proposed that may have greater significance for archaeological research. Ruddiman’s Early Anthropocene Hypothesis (Ruddiman  2003,  2007,  2013) considers that human impacts on climate began earlier, with the spread and intensification of agriculture during the Middle to Late Holocene, driving increased greenhouse gas emissions. Ruddiman (2007) argues that there have been no natural climate states in the Holocene. Lewis and Maslin (2015) look to the arrival of Europeans in the Americas for a ­globally synchronous marker of human impact. Their Orbis hypothesis proposes a boundary at 1610 ce, when a declining human population in the Americas drove rapid afforestation and CO2 uptake, marked by a reduction in atmospheric CO2 between 1570 and 1620 ce in Antarctic ice cores (Ahn et  al.  2012; Rubino et  al.  2013; Lewis and Maslin 2015).

­Orbital Pacing of the Ice Age Cycles On tens to hundreds of thousand-­year timescales, Earth’s climate is controlled by the amount and distribution of solar radiation received at the Earth’s surface (termed ­insolation), which is determined by the interaction of three long-­term, cyclic variations in the Earth’s orbit and axis (Berger 1988; Lisiecki and Raymo 2007): i)  Eccentricity of the orbit describes the cyclic change in the Earth’s orbit around the sun from near-­circular to elliptical and back, driven by the gravitational influence of varying planetary alignments. The cycle has two main periodicities, one that varies in length between 95 and 136 ka and is usually referred to as 100 ka, and another longer 413 ka cycle. Eccentricity is the main determinant of total insolation through time and modulates the effects of the precession and obliquity cycles, which rather influence the distribution of insolation at different latitudes. ii)  Obliquity of the ecliptic describes the change in the tilt of the Earth’s axis of rotation, measured relative to the plane of the Earth’s orbit (the ecliptic), from 21.39° to 24.36° and back, over a 41 ka cycle. Obliquity has a strong influence on seasonal variation in insolation,

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Quaternary Geochronological Frameworks

particularly at high latitudes, where increasing seasonality is experienced as the angle of tilt increases toward its maximum (when summers are closest to, and winters farthest from, the sun). Variation in the amount of high latitude insolation plays an important role in the growth and decay of large ice sheets, and obliquity appears to have been the main driver of the 41 ka ice age cycles prior to the Mid Pleistocene Transition (Raymo and Nisancioglu 2003). iii)  Precession is a 23 ka cycle that combines the effects of two cyclic phenomena: axial precession and orbital (or apsidal) precession, and appears to have greatest influence on mid to low latitude climate variability. Axial precession is the wobble of the Earth’s axial plane due to the gravitational pull of the sun and the moon, with the effect that the seasons appear to move around the sun on a 25.7 ka cycle. In our current orbit, the Southern Hemisphere summer and Northern Hemisphere winter occur when the Earth, in its elliptical orbit, is closest to the sun (perihelion). The Northern Hemisphere summer and Southern Hemisphere winter occur when the Earth is furthest from the sun (aphelion). Presently then, seasonal extremes are greatest in the Southern Hemisphere and reduced in the Northern Hemisphere. In approximately 11.5 ka time the situation will be reversed. Orbital precession, which denotes the ­rotation of the path of the elliptical orbit around the sun on a 113 ka cycle, further modulates the seasonal insolation differences. Whilst the astronomical theory of global climate change was first developed by Croll (1890) and refined more famously by Milankovitch (1941), the first clear evidence for orbital pacing of Earth’s ice age cycles was observed some decades later in studies of deep marine core sediments that revealed climate proxy variations, most notably oxygen isotope ratios, with similar periodicities to the orbital cycles (Hays et  al.  1976; Imbrie et  al.  1984). Subsequently, climate proxy variations on orbital timescales have been observed in many long, globally distributed, marine and terrestrial records (e.g. Ding et al. 2002; Lisiecki and Raymo  2007; Lambert et  al.  2008). The distinctive wavelength and form of the ice age cycles forms the basis of the marine oxygen isotope stratigraphy, which is used to correlate, and sometimes to date, Quaternary sequences.

­Marine Oxygen Isotope Stratigraphy Fine-­grained sediments, termed oozes, accumulate in much of the Earth’s oceans from the continuous settling, known as rain-­out, of marine microfossils and fine-­grained

clay (clastic) particles suspended in the water column. Marine organisms such as foraminifera, radiolaria, and diatoms, extract oxygen and other nutrients from the seawater they inhabit. After death, their tests (shells) rain-­out and are buried on the ocean floor, where they accumulate a record of changing ocean composition through time. Measurements of changing oxygen isotope ratios measured in benthic (bottom-­dwelling) foraminifera preserved in deep marine sediment sequences from around the world, reveal consistent quasi-­cyclic patterns that have been shown to record the global ice volume changes of the Pliocene to Pleistocene ice age cycles (Shackleton (1977); Figure 1.1). Three isotopes of oxygen occur in nature (16O, 17O, and 18O) and their ratios in ocean water are altered via fractionation processes, which cause the preferential enrichment or depletion of the lightest isotope, 16O. The ratio of the heaviest to lightest isotope, 18O to 16O, measured using mass spectrometry, is reported as a deviation from an internationally assayed standard mean ocean water (SMOW; Baertschi (1976) and is denoted as δ18O. The δ18O values of ocean sediments show that ocean water had distinctly different δ18O values during glacial and interglacial intervals (Figure  1.1), and this is largely due to the effect of the expansion and contraction of the cryosphere on the hydrological cycle (Shackleton 1987). More energy is needed to evaporate H218O molecules than H216O molecules, therefore in cold climate intervals, H216O is preferentially enriched in water vapour evaporated from the oceans. Ocean waters thus become relatively depleted in H216O and enriched in H218O. Cold temperatures also promote earlier precipitation of the heavier H218O molecule from clouds, whereas more H216O is precipitated further from the moisture source, for example at high latitudes, where it is then locked up in glacial ice. As climates warm, ice sheets melt and return their H216O-­enriched waters back to the oceans. Interglacial ocean waters are therefore less depleted in H216O, and the precipitation feeding a reduced cryosphere has a higher δ18O than during glacial times. Consequently, ocean sediments formed in cold climate intervals have relatively high δ18O values when compared to sediments formed under warm climate intervals. It is important to note that the opposite pattern is seen in ice (Figure 1.2). Ice formed within glacial times has relatively lower δ18O than during interglacials due to the preferential evaporation of H216O and earlier precipitation of H218O during cold ­climate conditions. Timescales for the global ice age cycles recorded in some of the earliest long marine δ18O records relied on assumptions of uniform sedimentation rates between horizons with age-­estimates derived from a range of methods (e.g. Shackleton 1977; Imbrie et al. 1984). Marine sediments

­Marine Oxygen Isotope Stratigraph 

Figure 1.2  The INTIMATE Event Stratigraphy, spanning 123–8 B2k (before the year 2000 ce), numbers and establishes the boundary ages for the Greenland stadials (white sections, GS-­) and interstadials (grey sections, GI) of the last glacial cycle (Rasmussen et al. 2014). Twenty-­year average values of δ18O (per mil) and Ca2+ (ppb) are shown for the GRIP (red), GISP2 (green), and NGRIP (blue) ice cores on the GICC05 timescale, with dots marking the match-­points for translation of the GRIP and GISP2 records onto the NGRIP GICC05 chronology. δ18O compositions from the NEEM ice core are appended for the Eemian interglacial to extend the NGRIP record. Source: Reprinted from Quaternary Science Reviews v.106, Rasmussen et al. (2014). Copyright (2014), with permission from Elsevier.

can be directly dated using radiocarbon dating (see Chapter 2) back to a limit of 50 ka BP and by the identification of absolutely dated horizons, such as magnetic reversals or ­volcanic ash beds (Chapter  8). Correlation of glacial and interglacial δ18O maxima and minima to dated features on land, such as sea-­level high-­stands, also provide chronological tie-­points (Shackleton  1977). Plotted on an age-­ scale, it is clear that the shape, amplitude, and frequency of the δ18O cycles recorded in marine sediments, and elsewhere, do not mirror the modelled orbitally-­driven insolation budget and have varied throughout the Quaternary (Figure  1.1). Evidence for the causal connection between insolation variability and the glacial–interglacial cycles was revealed by Hays et  al. (1976), who applied spectral analysis to a series of dated Pleistocene marine δ18O records, revealing climate variations concentrated in the 23, 42, and 100 ka frequency bands, correlated to the ­precession, obliquity and eccentricity cycles, respectively. Modulation of the orbitally-­driven insolation cycles by internal Earth system processes results in the so-­called ‘saw-­tooth’ asymmetrical patterns of the Middle to Late Pleistocene ~100 ka ice age cycles, observed in so many records, with rapid glaciations followed by more gradual and variable deglaciations (Figure 1.1).

Global compilations, or stacks, of marine δ18O records provide the basis for the marine isotope stage (MIS) system, which identifies and numbers the glacial (even ­numbered) and interglacial (odd-­numbered) stages through the Quaternary and back into the Pliocene, beginning with the present interglacial as MIS 1 (Emiliani  1955; Imbrie et al. 1984; Shackleton et al. 1995; Lisiecki and Raymo 2005). The landmark SPECMAP curve (Imbrie et al. 1984) compiled five marine planktonic δ18O records into a single orbitally-­tuned stack by using the pacing of the orbital cycles to derive a timescale for the observed δ18O oscillations of the last 300 ka. In this way, SPECMAP provided a first benchmark record of global climate through the Middle to Late Pleistocene that shaped geological, climatological, and archaeological studies for many years. SPECMAP was superseded by the ~5.3 Ma LR04 stack of Lisiecki and Raymo (2005), which comprises 57 globally-­distributed benthic marine δ18O records and provides an overview of global climate and sea-­level change since the Early Pliocene. The LR04 stack records and dates 102 ­isotope stages during the Quaternary (Figure 1.1), and ­consequently the stack is frequently used as a tuning or correlation target for subsequent oceanic and terrestrial palaeoclimate and/ or geological records that lack independent chronological

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Quaternary Geochronological Frameworks

control. The MIS numbering used today is based on LR04 and has evolved both in length and detail since the original work of Emiliani (1955), yet maintains established numbers for what are now seen as ‘sub-­stages’ within the Pleistocene (e.g. MIS 3–5 are sub-­stages of the last glacial cycle), and adds sub-­stages where further divisions have been recognized (e.g. MIS 5 is divided into MIS 5 a–e, and MIS 5e is recognized as the last interglacial).

­Magnetostratigraphy The Earth’s magnetic field, known also as the geomagnetic field, varies in both intensity and in its direction through time, due to instabilities in the fluid outer crust (see Chapter 6). On historic timescales, small-­scale movements of the geomagnetic poles relative to the geographic poles (geomagnetic secular variations) have been detected by instrumental measurements (Bloxham et al. 1989; Jackson et al. 2000). Geomagnetic field directions from further back in time are reconstructed from the measurement of the direction and intensity of the remnant magnetism preserved within particles in undisturbed sediment sequences (detrital remnant magnetism) and ferromagnetic minerals within igneous rocks (natural remnant magnetism). Directional changes may be full 180° polarity reversals between normal (i.e. as at the present) and reversed polarity, or, more frequently, they are excursions when the geomagnetic poles move by more than 45° equatorward but return to their pre-­existing alignment (Gubbins  1999; Roberts  2008). High-­resolution studies of magnetized rocks have shown that magnetic polarity transitions may be rapid or may take many tens of thousands of years (Channell et al. 2020). Most importantly, however, polarity transitions and excursions are registered synchronously around the globe and thus provide an invaluable tool for correlating and dating the geological record. The pattern and ages of polarity reversals make up the geomagnetic polarity timescale (GPTS) (Ogg 2012), which is integral to the IUGS Geologic Timescale (Figure 1.1). An interval corresponding to a magnetic polarity zone is termed a magnetic chron, and shorter-­lived polarity changes within a chron are designated as subchrons. The Quaternary comprises two chrons (Bruhnes and Matuyama), both of which are interrupted by a series of shorter-­lived subchrons and excursion events (Figure 1.1). Quaternary polarity reversals and excursions are either radiometrically-­dated in volcanic sequences using the 40 Ar─39Ar dating method (which has largely superseded K─Ar dating) and/or dated according to their position in orbitally dated marine sediment records (Ogg  2012; Channell et al. 2020). Where independent ages are available,

magnetic polarity events provide independent checks on the timescales of orbitally tuned marine and terrestrial sediment timescales. As an example, the Gauss normal to Matuyama reverse chron boundary, marking the base of the Quaternary, has been correlated to MIS 104 in marine sediment records with associated age estimates of between 2.59 and 2.60 Ma (Shackleton et  al.  1990; Hilgen  1991). The marine sediment ages are confirmed by an 40Ar─39Ar age of 2.606 ± 0.006 Ma generated from dating tuffs in a lake sequence in Kenya (Deino et al. 2006). The pattern of magnetic chrons, sub-­chrons and excursions preserved within Quaternary marine sediment δ18O stacks has also been used to correlate and date long terrestrial sequences, such as those from the Chinese Loess Plateau (e.g. Ding et al. 2002) and from ancient lakes such as that of the El’gygytgyn impact crater in Siberia (Nowaczyk et al. 2013b). The consistency seen in the frequency and amplitude of glacial–interglacial oscillations recorded in long marine and terrestrial sequences, checked by independent dating, is key evidence for teleconnections in the global climate system and the dominant role of orbitally-­driven climate cycles. The geomagnetic field extends into space, where it interacts with incoming solar winds and influences the galactic cosmic ray flux that produces cosmogenic nuclides (e.g. 14C, 10Be, 26Al, and 36Cl) in Earth’s atmosphere, which then accumulate on the Earth’s surface. Past variations in the geomagnetic field strength, such as the ~1000 year-­long 41 ka BP Laschamp excursion (Channell et  al.  2020), can therefore also be revealed by sequential measurement of cosmogenic nuclides within accumulated geological sequences. Measurements of both 14C and 10Be have been used in marine and lake sediments to detect the Laschamp excursion (Nilsson et al. 2011; Nowaczyk et al. 2013a), and 10 Be is also used in ice core sequences (Raisbeck et al. 1992; Yiou et  al.  1997). Alignment of the cosmogenic isotope ­signals of geomagnetic excursions provides a climate-­ independent dating and correlation tool for the precise comparison of palaeoclimate sequences (Muscheler et  al.  2004; Bronk Ramsey et  al.  2014). Such methods become increasingly important as we consider the drivers and impacts of the sub-­orbital scale variations observed globally in terrestrial and marine palaeoclimate records of the Middle to Late Pleistocene.

­Polar Ice Core Chronologies At ice sheet summits or divides, where glacial flow is minimal, seasonal snow-­fall layers accumulate and are compacted into long layered sequences of ice that also trap atmospheric gases and particulate matter and can be

­Polar Ice Core Chronologie 

sampled by the extraction of an ice core (see Chapter  9). Polar ice core records provide continuous multiproxy palaeoclimate reconstructions of different lengths, with the longest spanning back to the start of the Middle Pleistocene (Wolff et  al. (2010a)). As in marine sediment sequences, oxygen isotope ratios act as a proxy for ice volume and are complemented by a suite of chemical and physical ice and gas phase measurements that paint a detailed picture of global climate conditions (Alley 2000). The longest continuous ice cores are found in Antarctica, where ice has been accumulating since the Oligocene (Siegert et al. 2008). The EPICA Dome C core reaches back to 800 ka BP and captures the saw-­tooth pattern of climate change over the last eight glacial–interglacial cycles (Lambert et  al. (2008), Wolff et  al. (2010a); Figure  1.3). Much like marine core sequences, age models for the longest Antarctic ice cores rely on the tuning of proxy signals, typically δ18O, to orbital parameters (e.g. Landais et al. 2012; Bazin et al. 2013). Inter ice-­core correlations, volcanic isochrons, and comparisons

to speleothem records provide independent constraints over some intervals (e.g. Bazin et al. 2013; Veres et al. 2013; Buizert et al. 2015a; Svensson et al. 2020). Continuous ice core records from the summit of the Greenland ice sheet reach only to the Last Interglacial at ~123 ka BP (Rasmussen et  al.  2014), however folded ice from the base of the North Eemian Project (NEEM) core has been used to reconstruct the Last Interglacial (Eemian) climate conditions (Dahl-­Jensen et al. 2013). Higher snow accumulation rates and greater annual layer thicknesses in Greenland summit cores, compared to the long core sites in Antarctica, means that many proxy signals can be measured at seasonal to annual resolution (Alley  2000; Steffensen et al. 2008). Multiple ice cores from Greenland have been cross-­correlated using volcanic markers and proxy signals to verify annual layer counting and generate a master Greenland Ice Core Chronology, GICC05 (Andersen et  al.  2006; Rasmussen et  al.  2006; Svensson et  al.  2006). The independent chronological control and

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Figure 1.3  The signature of the precession cycle on global hydroclimate is demonstrated by the correspondence between (a) July insolation at 65°N. Source: Adapted from Cohen and Gibbard (2019). (b) The ~640 ka Asian Monsoon Chronology (cross-­correlated speleothem calcite δ18O records from Hulu Cave, Dongge Cave, and Sanbao Cave, in China. Source: Adapted from Cheng et al. (2016) and https://www.ncdc.noaa.gov/paleo-­search/study/20450. Comparison to (c) Antarctic temperature reconstructions (δD from EPICA Dome C, on AICC2012. Source: Adapted from Bazin et al. (2013); Jouzel et al. (2007) and https://www.ncdc.noaa.gov/paleo/ study/15076. and (d) the LR04 Marine Isotope Stack (Lisiecki and Raymo 2005) identify packages of four to five procession cycles took place between each of the last seven glacial terminations. Source: Adapted from Cheng et al. (2016).

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annual to seasonal proxy resolution afforded by the Greenland ice core records reveals the detail of millennial-­ scale stadial–interstadial oscillations throughout the last glacial cycle (Wolff et  al.  2010b; Rasmussen et  al.  2014) with continuity and dating precision unavailable in most continental or marine sediment archives. The Greenland Event Stratigraphy (Rasmussen et al. 2014) proposed by the INTegrating Ice core MArine and TErrestrial Records (INTIMATE) palaeoclimate research network (Björck et al. 1998; Lowe and Hoek 2001; Walker 2016), uses GICC05 to number and establish dates for stadial–interstadial transitions back to 123 ka BP (Figure 1.2) as well as dating widespread volcanic ash layers and abrupt (­centennial–decadal scale) climate events (Blockley et  al.  2014). The GICC05 timescale is additionally used as a tuning target for the younger portions of the Antarctic Ice Core Chronology, with records from the two hemispheres correlated using their atmospheric methane signals, which covary due to the rapid mixing of methane in Earth’s atmosphere, and patterns of volcanic marker layers (Raisbeck et  al.  2007; Veres et  al.  2013; Muscheler et  al.  2020). More widely, the  Greenland Event Stratigraphy is used as a stratotype for  North Atlantic palaeoclimatic change; however, the uncritical use of GICC05 ages in archaeological or palaeoenvironmental studies, without demonstration of ­synchroneity, should be avoided. The deep West Antarctic Ice Sheet Divide (WAIS Divide) ice core in Antarctica has comparable resolution to the Greenland ice core records and provides a chrono-­ stratotype for palaeoclimate in circum-­Antarctic regions (Buizert et al. 2015b). The WAIS Divide WD2014 chronology reaches back to 68 ka BP and is based on independent annual layer counting back to 31.2 ka BP (Sigl et al. 2016). Precise comparisons of the annually resolved Greenland and WAIS Divide ice core proxy records have been made, with the records beyond 31.2 ka aligned using the correspondence between the down-­core methane signal and the NGRIP δ18O record (Buizert et al. 2015a). The results detail the pace and asynchronous nature of Northern and Southern Hemisphere climate oscillations on sub-­orbital timescales, providing critical insights into global climate teleconnections (Buizert et al. 2015a; Markle et al. 2017). Holocene polar ice core records capture and date the high-­latitude atmospheric signals of short-­lived (decadal– centennial) climate fluctuations in the Holocene Epoch, such as the abrupt cooling at the 8.2 ka event (Alley et  al.  1997; Rasmussen et  al.  2007; Thomas et  al.  2007). Despite being so far from areas of human occupation, the ice cores also capture atmospheric signals of anthropogenic activity. Analyses of the gases in air bubbles in Antarctic ice cores trace the sharp increase in atmospheric greenhouse gas compositions since the Industrial

Revolution (Etheridge et al. 1996; Siegenthaler et al. 2005; MacFarling Meure et  al.  2006; Ahn et  al.  2012). Nitrates, sulfides, lead and other aerosols deposited on the surface of the ice sheets record increases in pollution, particularly related to fossil fuel combustion, since the late nineteenth century (Mayewski et al. 1986, 1990; Vallelonga et al. 2002; McConnell et  al.  2014). The ice cores also capture more localized, smaller-­scale mining and smelting signals from pre-­industrial times (Rosman et  al. (1997); see also Chapter  9). For example, a subannually-­resolved 1100 bce–800 ce record of lead pollution from the NGRIP ice core has been shown to correlate with the history of silver-­ lead mining and smelting in the Phoenician, Carthaginian, and Roman empires (McConnell et al. 2018).

­Speleothem Composite Chronologies In mid-­ to low-­latitude carbonate cave systems where the hydrological and geological conditions are suitable, the precipitation of calcite or aragonite from dripwater forms layered speleothems (stalagmites, stalactites, and flowstones) that may grow near-­continuously for many ­thousands of years (Atsawawaranunt et  al.  2018). Cave dripwater ultimately derives from infiltrated rainfall and, if precipitated in equilibrium, calcite δ18O, δ13C, chemistry, and growth rates provide proxies for local hydroclimate and regional to global atmospheric processes (McDermott  2004; Lachniet  2009; Atsawawaranunt et  al.  2018). Speleothem calcite can be directly dated using U-­series techniques (see Chapter 5) and statistical interpolation (age-­modelling) between dated samples (Scholz et al. 2012). The 230Th-­dating method can generate high precision dates (uncertainties 0.2 wt%) are required, and ideally, trace elements (in ppm) should be used to verify the correlation. The precision and accuracy of the data should be

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Figure 8.6  Major element (a) and trace element (b) glass shard compositions from volcanoes across Japan, extending from southwest (left on the legend) through to northeast (right) (Albert et al. 2019b). Data from each volcano is presented as a coloured field, which is based on individual glass shard analyzes of proximal tephra layers associated with various eruptions. Note that the major element compositions of some volcanoes are similar to those of others, but they have distinct trace element compositions. Some glass shard analyzes from specific tephra layers in the Lake Suigetsu core are shown, and they have been correlated to specific volcanoes (colour) and eruptions (in brackets on the legend) apart from one tephra that it is from an eruption of Hakone volcano that has not yet been identified elsewhere. Source: Adapted from Albert et al. (2019b).

demonstrated by analyzing secondary standards with well-­known compositions, e.g. the MPI-­DING reference glasses (Jochum et  al.  2006), in the same analytical batch as the samples.

ii)  Ideally, the tephra that is being correlated is a well-­ known unit within a tephrostratigraphic framework. The tephrostratigraphy is built up through mapping and measuring the thickness and grain-­size

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characteristics of the deposits in the regions surrounding the vent (e.g. eruption history of Campi Flegrei, Italy in the last 15 ka; Smith et al. 2011), and tracing the deposits into medial-­distal locations where they may be interbedded with tephra layers from other volcanoes (e.g. the Lago Grande di Monticchio lake core; Wulf et  al.  2004). A tephrostratigraphy presents a detailed explosive eruption record of volcanoes within a region. Due to preservation issues such as erosion and weathering, and limited exposure due to burial, the eruption records typically become less complete back through time with comprehensive eruption records only known for the most recent activity. Unfortunately, the tephrostratigraphies are only well developed for some regions, e.g. Iceland (e.g. Haflidason et al. 2000; Meara et al. 2020), New Zealand (e.g. Hopkins et  al.  2021), and Honshu Island, Japan (e.g. Albert et  al.  2019b) and are often lacking sufficient detail in some particularly volcanically active regions. For example, there are only long-­term and detailed eruption histories for a few volcanoes in Indonesia (Fontijn et al. 2015, Bouvet de Maisonneuve and Kuvikas  2020), and there is nothing comprehensive for the region due to poor tephra preservation in the tropical climate. Correlating a tephra layer with glass chemistry to a known eruption within a tephrostratigraphic framework is ideal, but it is not completely necessary for correlations. Distal layers can be correlated, e.g. tephra layers within different excavation pits within an archaeological site if there is additional evidence to support the correlation. iii)  Chronological constraints, such as radiocarbon dates, other tephra correlations or other contextual information, above and below the tephra in the sequence ensure that the correlation makes sense.

­Relative Chronology Correlations using tephra provide a relative chronology, with the tephra positions marking the same point in time. Such correlations can compare changes at different sites by linking data from the same or different paleoenvironmental proxies or human cultural indicators. For example, the CI tephra layer from the large eruption of Campi Flegrei (Italy) is a widespread marker across central and eastern Europe and is found as a cryptotephra in various archaeological sites in Libya (Huau Fteah), Bulgaria (Kozarnika), and Greece (Klissoura and Franchthi) (Lowe et al. 2012). The tephra is found at the transition between the Middle and Upper Palaeolithic assemblages at Franchthi (Greece), but at other sites, it occurs within the Upper Palaeolithic

and often at the start of the Early Aurignacian. These relative correlations are further evidence that Neanderthals were still occupying some sites at the time of the CI eruption at 40 ka, while anatomically modern humans were already occupying others. The position of cultural changes relative to the CI isochron indicates that the eruption did not drive the demise of Neanderthals as their populations were already in decline (Lowe et  al.  2012). The cultural assemblages were also correlated to the LC21 Aegean marine core and its high-­resolution palaeoenvironmental proxy data (Grant et al. 2012) using the CI tephra. This synchronization of archaeological and palaeoclimate information clearly indicates that anatomically modern humans were occupying sites prior to the start of the dramatic cooling event known as the Heinrich event 4. Even though the CI was an enormous eruption that covered a wide area in tephra during a particularly cold period, there is no evidence for a long-­lasting effect on the anatomically modern human populations at sites covered in thin layers of ash (Lowe et al. 2012).

­Dating Tephra Deposits Volcanic deposits can be dated using many commonly employed radiometric dating methods. Here we outline the methods that can be used to estimate the age of an eruption. Once ages are obtained for the eruptions their tephra layers can be used as age markers, and the dates can be imported into the age models of sequences in which the tephra are found.

Radiocarbon Dating Eruptions are often dated using the radiocarbon method, which is discussed in Chapter 2. Volcanic deposits are well suited to the method as charred organic material is often found within PDC deposits as the hot (hundreds of °C) energetic flows rip up and burn vegetation while moving across the landscape. In addition, small fragments of charred organic material are commonly discovered in soils underlying the eruption deposits. Given that there are also numerous radiocarbon laboratories around the world offering commercial services, this technique is extensively used to date eruptions in the last 50 ka. Countless eruptions have been dated using the radiocarbon method, but here we highlight a couple of recent studies which have obtained very precise dates for large magnitude eruptions. The date of the Taupo M6.9 eruption from Taupo caldera, New Zealand was determined by dating sections through a tree that was felled by the initial blast and subsequent PDC. Successive radiocarbon

­Dating Tephra Deposit  143

measurements of decadal tree-­ring samples, which extended from the inner heartwood to the bark of the tree, were wiggle-­matched onto the radiocarbon calibration curve to yield a date of 232 ± 5 ce for the eruption (Hogg et al. 2012). Another example is the recent study by Oppenheimer et al. (2017), which dated the M6.8  Millennium Eruption of Changbaishan volcano (­border of China and North Korea; (Figure 8.3)) to late 946 ce. They found a tree buried within the PDC that they were able to date using annually-­resolved radiocarbon measurements and by counting tree rings. The precision of the date was refined by identifying the anomalous spike in 14C due to a surge in cosmogenic radiation, termed a Miyake event, that occurred at 775  ce (Miyake et al. 2012). This radiocarbon age combined with tree-­ring counts is consistent with dates obtained from other records, including the date of the tephra peak in the Greenland ice core (Sun et al. 2014). Interestingly, historical texts indicate that loud sounds were heard about 470 km east of Changbaishan in 946 ce and that there was ash fallout in Nara (Japan) on 3  November 946  ce (Oppenheimer et al. 2017), and although these observations are not necessarily associated with the Millennium Eruption they are consistent with the magnitude and ash dispersal of the event.

Luminescence Dating The luminescence dating method establishes the time since a mineral was last exposed to sunlight or heat. The signal in the minerals can be measured by thermal or optical stimulation, and these methods are referred to as thermoluminescence and optically stimulated luminescence, respectively (see Chapter 4). Given that magmas crystallize at high temperatures and their melt quenches to glass, tephra deposits are, in theory, ideal for luminescence dating. Various researchers have tried to date the glass, and quartz and feldspar minerals that commonly crystallize within the magmas, but they have had limited success (e.g. Tsukamoto et  al.  2007). It seems that these components produce unstable signals and low signal to noise, which is related to anomalous fading and is thought to be associated with rapid cooling that generates lattice disorder in the crystal structure (Bösken and Schmidt  2020). However, lithic material within the tephra deposits and, in particular, the non-­volcanic country rock is suitable (e.g. Preusser et  al.  2011). The luminescence signal in these lithic fragments is typically reset during the eruption when they are heated and/or experience high-­pressure shock (Rufer et  al.  2012) and thus are more suitable for luminescence dating than the volcanic material. The anomalous fading observed in volcanic glass and minerals results in an underestimation of the age and means that luminescence techniques cannot be used to

date volcanic material. However, it is possible that the recent advances in luminescence techniques, the use of different protocols, and the targeting of specific luminescence emissions may allow more stable signals to be acquired, which may permit volcanic glass and minerals to be dated using luminescence techniques in the future (Bösken and Schmidt  2020). In the meantime, the lithic fragments of non-­volcanic material found in the eruption’s PDC deposits should be used for luminescence dating.

K─Ar and 39Ar/40Ar Dating Volcanic deposits can be dated using the K─Ar dating method, which has been superseded by the 39Ar/40Ar ­technique. The K─Ar method requires the amount of potassium-­40 remaining in the sample and the argon-­40, the product of radiogenic decay of 40K by electron capture, to be measured. In the 39Ar/40Ar method, 39Ar is instead used as a proxy for 40K. The ratio of 40K to 39K is known, and the 39K is converted to 39Ar by placing the sample in a nuclear reactor. All the argon isotopes are then measured on the same mass spectrometer on both the unknown sample and a known age sample (standard) that was irradiated with the sample, and precise ratios of these allow the age of the unknown eruption to be calculated (McDougall and Harrison 1999; Guillou et al. 2021). The half-­life of 40K is 1.25 Ma, and this means that the method can be used to reliably date all K-­bearing unaltered rocks on Earth that are less than 3 billion years old. Potassium is present in all magmas but some have much more than others, with some volcanoes crystallizing particularly K-­rich phases such as sanidine (K-­feldspar), biotite, hornblende, and leucite. The method is better suited to samples that are hundreds of thousands to millions of years old as more 40Ar has accumulated, which allows for better determination. However, recent advances in mass spectrometry have reduced the detection limits of the instruments, and now K-­rich crystals that are tens of thousands of years old can be precisely dated. The 39Ar/40Ar method has been used to date the M9.1 Younger Toba Tuff eruption from Toba, Indonesia, the largest eruption known to have occurred on Earth in the last 1 Ma. An age of 75.0 ± 0.9 ka (1 σ) was obtained for the widely dispersed deposits by analyzing feldspar and biotite crystals from the proximal deposits around the caldera on the island of Sumatra, Indonesia, and the distal deposits found in archaeological sites in India that are >2500 km from the vent (Mark et  al.  2014) (Figure  8.3). Furthermore, the widespread CI eruption deposits have been dated using 39 Ar/40Ar methods, and precise age of 39.85 ± 0.12 ka (95% confidence level) was obtained by analyzing single K-­feldspar crystals (Giaccio et al. 2017).

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Zircon Double Dating: U─Th-­disequilibrium/U─Pb and (U─Th)/He Dating This method employs (U─Th)/He and U─Th-­ disequilibrium or U─Pb methods to date zircon crystals that often crystallize in magmas. The method is commonly referred to as ZDD as the zircon crystals are dated using the (U─Th)/He geochronometer and the U─Th-­disequilibrium or U─Pb geochronometer (Danišík et al. 2017). The (U─Th)/He method requires the determination of radiogenic helium (4He), produced by the alpha decay of 238 U, 235U, 232Th, and 147Sm, and the measurement of the remaining concentrations of the parent isotopes (Farley  2002). The 4He is particularly mobile at high temperatures so it only accumulates when the crystals are below 150 °C and thus, the geochronometer provides an eruption age. The (U─Th)/He method can be applied to eruption deposits as young as 2.5 ka and extends back to ~1.5 Ma, but it needs to be coupled with U─Th-­disequilibrium and U─Pb methods for the disequilibrium correction (Farley 2002). The U─Th-­disequilibrium is used for eruptions that have occurred within the last 375 ka, while the U─Pb geochronometer is used for eruptions that are >375 ka (Danišík et al. 2017). These methods are required to assess the secular disequilibrium in the U-­decay chains, obtain the 230Th/238U activity ratio, and constrain the magma residence time prior to the eruption (Farley  2002). The (U─Th)/He ages also need to be corrected for the He loss due to alpha recoil, which is related to the distribution of the parent nuclides in the crystal as well as the size and shape of the crystals (Danišík et al. 2017). Advances in the (a)

(b)

measurements and corrections mean that ZDD can now be used to provide both accurate and precise eruption ages, and the method will undoubtedly be increasingly used to date volcanic deposits that contain zircon. Although zircon is found in the deposits of large explosive eruptions, the abundance is typically around 1–2% by volume and thus large volumes of material must be sampled. The ZDD method has been used to date various eruption deposits, including deposits of recent eruptions from Hasan Dagi volcano in Anatolia, Turkey. Zircons were extracted from pumice deposits of two separate eruptions that are exposed around the volcano, and the ZDD method was used to obtain an age of 8.97 ± 0.64 ka for the HD eruption and 28.96 ± 1.5 ka for HAD eruption (Schmitt et al. 2014). The age of the HD eruption coincides with the occupation of the Neolithic site of Çatalhöyük, which is situated 130 km away (Figure 8.7). In particular, the eruption occurred while level VII was occupied, and the 3 m-­long ‘map’ mural on the N and E wall of shrine 14 was created (Meece 2006). Given the temporal overlap, Schmitt et al. (2014) argue that this mural depicts the HD eruption from Hasan Dagi volcano with the Çatalhöyük settlement in the foreground (Figure 8.7).

Fission Track Dating Volcanic deposits can be dated by counting the fission tracks that have formed in the volcanic glass (Westgate 1989) or apatite and zircon crystals from the radiogenic decay of  238U. These ion tracks can be observed by etching and S

1m

(c)

Turkey Hasan Dagi ˘

Çatalhöyük

100 km

N

Figure 8.7  (a) The ‘map’ mural on the N and E wall of shrine 14 in level VII at the Neolithic Çatalhöyük site in Turkey. Source: Meece (2006)/Cambridge University Press. The mural is thought to represent the Çatalhöyük settlement and the HD eruption of Hasan Dagi (b, c) volcano (Schmitt et al. 2014). Source: Schmitt et al. (2014)/(b) Public Library of Science/CC BY 4.0 (c) PLOS ONE.

­Archaeological Case Studie 

polishing the surfaces, and their density relates to the age of the sample. The amount of 238U remaining in the sample has to be measured for age determination, which is usually determined using a method involving neutron irradiation. The irradiation induces fission of 235U, and the resulting density of the induced tracks on an external detector is used as a proxy for 238U as the ratio between the two ­uranium isotopes is known and constant. The method is typically used to date volcanic deposits that are >75 ka and has been used to estimate the ages of many large eruptions from volcanoes in New Zealand and Indonesia (e.g. Westgate et al. 1998).

Dating Tephra Layers Using Age Models By correlating tephra layers into distal archives, it is possible to use the chronology of the distal records to provide a date for the eruption. This is particularly useful if the distal record has a high-­resolution chronology, such as a detailed Bayesian age model based on various chronological constraints (Ramsey 2008). Tracing eruption deposits into well dated, modelled sequences provides precise ages for eruptions that were not recorded in historic times. Records that preserve seasonal layers that can be counted are particularly useful for chronology, such as ice cores or varved lake sequences. For example, a date of between 7.165 and 7.303 cal ka BP has been determined for the Japanese (K─Ah tephra) eruption from Japan (McLean et al. 2018) by identifying the position of tephra in the Lake Suigetsu sediment core (Figure  8.3), which has a particularly detailed age model that is based on varve counts and a large number of radiocarbon dates (Ramsey et al. 2012). The M7.2 Akahoya eruption of Kikai caldera, southern Kyushu Island, Japan, dispersed 200 km3 of ash (Maeno and Taniguchi 2007) and deposited a 3 cm tephra in Lake Suigetsu, which is situated 750 km from the volcano (McLean et al. 2018). The K─Ah tephra forms an important marker layer across Japan and interrupted occupation at numerous Jomon sites in southern Japan (Moriwaki et al. 2016). The chronology for the Greenland ice cores is reliable back to at least 60 ka and is based on seasonal ice layers that are counted visually and through variations in composition (Ca2+, Na+, NH+4, SO2−4, NO−3) and electrical conductivity (Svensson et al. 2008) (see Chapter 9). Numerous studies have located tephra within the Greenland ice cores, and so this ice core chronology can be used to provide precise dates for the eruptions, e.g. a date of 431 ce has been assigned to the Tierra Blanca Joven eruption from Ilopango, El Salvador based on the position of the tephra in a Greenland ice core; a significant improvement on previous radiocarbon determinations (270–562 ce) (Smith et al. 2020). This places the eruption within a phase of Maya expansion

in central America suggesting that the impact of this enormous (M6.9–7.3) eruption was not particularly pronounced or long-­lived in regions >80 km from the volcano (Smith et al. 2020).

­Archaeological Case Studies There are various instances where volcanic eruptions have served archaeology. Well-­known cases are Pompeii and Herculaneum, which are situated on the lower slopes of Vesuvius and on the edge of the Bay of Naples, Italy; and Akrotiri (Figure  8.2) on the island of Santorini, Greece. The 79 ce and Minoan eruptions of Vesuvius and Santorini, respectively, buried the towns preserving a detailed snapshot of life in those times. Evidence from the objects that were found has provided insight into trade, how the societies operated, and what they valued at the time. In the case of Akrotiri, seeds from one of the storage jars within a building in the village were dated to provide a precise date of 1611–1683 bce (2 σ) for the eruption (Manning et al. 2006). Tephra layers are also used to provide ages for hominin fossils in Africa. Large volcanic eruptions have deposited thick tephra sequences in the North East African Rift and covered archaeologically and anthropologically important sites in Ethiopia and Tanzania. Numerous hominin fossils have been found in relation to tephras that have been dated using K─Ar, and more recently by 40Ar/39Ar techniques. Olduvai Gorge in Tanzania is arguably one of the most important sites for understanding human evolution. It is located within the Great Rift Valley, where the tectonic plates are moving apart, which causes faulting that facilitates magma intrusion and eruption. The rift valley has been volcanically active for millions of years with eruptions ranging from small, non-­explosive events that produce lava flows through to enormous explosive eruptions generating eruption plumes and dispersing ash over wide areas. Numerous tephra layers are found in Oludvai and have been used to constrain the ages of the fossil hominins to around 1.8 Ma for Homo habilis (Johanson et al. 1987) and the slightly younger Paranthropus boisei (Domínguez-­ Rodrigo et al. 2013), 1.2 Ma for Homo erectus, and 17 ka for Homo sapiens (Hay 1976). Olduvai Gorge is the earliest site (1.7 Ma) with evidence for Acheulean technology (Diez-­ Martín et  al.  2015). The ages for these tephra units were largely determined using K─Ar techniques in the 1970s, but now the more precise 40Ar/39Ar technique has been used to date some of the units. The age of the earliest hominin occupation of Italy has been constrained by 40Ar/39Ar methods. Numerous Acheulean handaxes and a Homo heidelbergensis femur were found in the Notarchirico archaeological site in

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Basilicata (Pereira et al. 2015). The site is close to the Monte Vulture volcano that was particularly active between 740 and 490 ka, with numerous tephra layers preserved in the fluvial sequence. 40Ar/39Ar ages of sanidine crystals date hominid occupation at the site to 670 ± 4 ka, which is the earliest in the region. The most recent eruption from Monte Vulture occurred at around 140 ka, and it generated the crater that is now infilled by a lake called Lago Grande di Monticchio (LGdM). The sediments that have accumulated in this lake preserve numerous tephra layers and provide an invaluable record of explosive volcanism in Italy spanning the last 130 ka (Wulf et al. 2004). Two of the tephra layers preserved in LGdM have been found more than 1000 km away in the Haua Fteah cave in northeast Libya (Douka et al. 2014). Haua Fteah has been investigated since the 1950s with detailed excavations. There is evidence of occupation from the Middle Palaeolithic. The chronology of the site was recently revisited using a multi-­method approach that involved obtaining new radiocarbon dates, identifying tephra layers, and dating crystals within the sediment using optically stimulated luminescence and electron spin resonance techniques (Douka et al. 2014). In all, four tephra layers were identified in the excavated sequence. The glass compositions allowed two layers, a 1 cm visible tephra and a cryptotephra, to be correlated to the 16.49–17.92 cal ka BP Biancavilla Ignimbrite eruption of Mount Etna, Sicily, and the 40 ka CI eruption from Italy, respectively. Another cryptotephra has the same chemistry as a layer in the LGdM core, which has been dated using the core’s varve chronology to 68.62 ± 2.06 ka. These three eruption ages were imported into the Bayesian-­based age model and integrated with other chronological data from the Haua Fteah

sequence to constrain the various cultural occupations at the site, which span from the Pre-­Aurignacian at 101.6 ka through to Neolithic occupation that started at 5.2 ka (Douka et al. 2014).

­Conclusions Large eruptions disperse ash over continental-­scale areas and form marker layers that can be exploited for chronological purposes. In the last couple of decades, there have been numerous papers and reviews focused on tephrochronology (e.g. Lowe  2011). There have been significant improvements to the tephrostratigraphies spanning the last 150 ka of various volcanoes and regions, a few examples of which are: the central Ethiopian Rift (Fontijn et  al.  2018); central (Aeolian Islands, Italy; Albert et  al. (2017)); eastern Europe (Santorini volcano, Greece; Wulf et al. (2020)); and Japan (Albert et al. 2019b). Furthermore, the dispersal and timing of some of the largest eruptions in Earth’s history have been better constrained. These widespread ash layers and tephra layers within a well-­defined tephrostratigraphy can be used to provide a relative and absolute chronology for archaeological profiles and palaeoenvironmental sequences. They have been used to synchronize various records, providing high-­resolution insight into the relative timing of occupation at sites and highlighting time transgressive changes. Although the potential of tephrochronology has been demonstrated, the method has not yet been fully exploited. Tephrochronology will be increasingly used in the coming years to decades as ages of eruptions become better constrained, and the tephrostratigraphies of regions are refined.

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Oppenheimer, C., Wacker, L., Xu, J. et al. (2017). Multi-­proxy dating the ‘Millennium Eruption’ of Changbaishan to Late 946 CE. Quaternary Science Reviews 158: 164–171. Pereira, A., Nomade, S., Voinchet, P. et al. (2015). The earliest securely dated hominin fossil in Italy and evidence of Acheulian occupation during glacial MIS 16 at Notarchirico (Venosa, Basilicata, Italy). Journal of Quaternary Science 30: 639–650. Preusser, F., Rufer, D., and Schreurs, G. (2011). Direct dating of Quaternary phreatic maar eruptions by luminescence methods. Geology 39: 1135–1138. Pyle, D.M. (1989). The thickness, volume and grainsize of tephra fall deposits. Bulletin of Volcanology 51: 1–15. Pyle, D.M. (2000). Sizes of volcanic eruptions. In: Encyclopedia of Volcanoes (ed. H. Sigurdsson, B. Houghton, H. Rymer, et al.), 263–269. San Diego, CA: Academic Press. Pyle, D.M., Ricketts, G.D., Margari, V. et al. (2006). Wide dispersal and deposition of distal tephra during the Pleistocene ‘Campanian Ignimbrite/Y5’ eruption, Italy. Quaternary Science Reviews 25: 2713–2728. Ramsey, C.B. (2008). Deposition models for chronological records. Quaternary Science Reviews 27: 42–60. Ramsey, C.B., Staff, R.A., Bryant, C.L. et al. (2012). A complete terrestrial radiocarbon record for 11.2 to 52.8 kyr B.P. Science 338: 370–374. Rufer, D., Gnos, E., Mettier, R. et al. (2012). Proposing new approaches for dating young volcanic eruptions by luminescence methods. Geochronometria 39: 48–56. Sarna-­Wojcicki, A.M., Shipley, S., Waitt, R.B. et al. (1981). Areal distribution, thickness, mass, volume, and grain size of air-­fall ash from the six major eruptions of 1980. In: The 1980 Eruptions of Mount St. Helens, Washington (ed. P.W. Lipman and D.R. Mullineaux), 577–600. Washington, DC: U.S. Dept. of the Interior. Schmitt, A.K., Danišík, M., Aydar, E. et al. (2014). Identifying the volcanic eruption depicted in a Neolithic painting at Çatalhöyük, Central Anatolia, Turkey. PLoS One 9: e84711–e84710. Smith, V.C., Shane, P., and Nairn, I.A. (2005). Trends in rhyolite geochemistry, mineralogy, and magma storage during the last 50 kyr at Okataina and Taupo volcanic centres, Taupo Volcanic Zone, New Zealand. Journal of Volcanology and Geothermal Research 148: 372–406. Smith, V.C., Isaia, R., and Pearce, N.J.G. (2011). Tephrostratigraphy and glass compositions of post-­15 kyr Campi Flegrei eruptions: implications for eruption history and chronostratigraphic markers. Quaternary Science Reviews 30: 3638–3660. Smith, V.C., Isaia, R., Engwell, S.L., and Albert, P.G. (2016). Tephra dispersal during the Campanian Ignimbrite (Italy) eruption: implications for ultra-­distal ash transport during

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Section 2 An Introduction to Quaternary Climate Change and Human Evolution and Adaptation Simon Blockley Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, London, UK

At the time of publication of the previous iteration of this handbook, there was considerable interest in some areas of archaeology on the nature of Quaternary environmental change and its role in driving human adaptation and evolution. In all areas of archaeology, an understanding of the environmental setting of any site or context is, of course, essential. In some particular areas of the discipline, however, reorganization of natural environments by long-­term cycles of glaciation meant that there was significantly more potential influence of climate change. In the archaeological record of the current Holocene interglacial environmental, archaeology was a key tool mainly for adding the local environmental context to human occupation and behaviour in a particular area. In the years that have followed, two key elements have added a new dynamic to the role that palaeoenvironmental reconstruction plays in archaeology. The first of these is a growing interest, both within archaeology and wider society, of the nature and influence of climate change, as archaeological priorities and perspectives are always influenced by the prevailing concerns of society (Trigger 2006). The second element is a much deeper understanding within the community researching past climates and environments that climate change can be significant and abrupt across a range of temporal scales (as summarized in detail in Lowe and Walker (2014)). As we shall see below and in other chapters in this section, this means that climate can change within less than 20 years, in both warm interglacial periods such as the one in which we now live (e.g. Cheng et al. 2009) and in multiple episodes during cold but unstable glacial times (e.g. Steffensen et al. 2008). This realization has had a significant impact on archaeology and archaeological science

over the last 20 years and is reflected in the revised chapters in this handbook. For example, the addition of a new chapter on ice core and marine records of Quaternary environmental change (Chapter  9) highlights the importance of these records in setting out an overarching narrative of past climate change. Additionally, new chapters on environmental controls on human dispersal and adaptation (Chapter 15) and Holocene climates and climatic events/ human impacts (Chapter  16) reflect the impact that advances in our knowledge of the nature of change has had on archaeology. At the same time, there have been technical advances across all approaches to environmental reconstruction, and each chapter in this section has been revised to reflect new techniques and insights from environmental disciplines with relevance for archaeology. An example is the inclusion of the lake records section (Chapter  12), as there has been a range of studies that use both peat and lake records to test for changes in climate and environment at the local, regional and global scale (below), and tie these directly to changes in the archaeological record (e.g. Brown 2008; Lowe et al. 2012; Blockley et al. 2018a).

­What is the Quaternary? This section is about change during a period of time known as the Quaternary, and in the last 20 years not only have we learned much more about Quaternary environments, but the concept of the Quaternary has also been redefined. Since the last version of this book the range of the Quaternary has been extended in time to encompass the period from the present to 2.58 million years ago (Gibbard

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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et al. 2010). While at one point the term Quaternary almost disappeared as a formal geological period, with a proposal that it was subsumed into the Late Neogene, it has now become the geological period that is most closely associated with the appearance, evolution and dispersal of our genus Homo and species Homo sapiens (deMenocal 2011). Climate change in the Quaternary, and the resulting environmental transitions, is a key factor, in determining who we are as a species and how we came to inhabit a whole planet, from our ancestral African home. Some of these questions are discussed in Chapter 15 and climate forcing factors, along with some key records discussed elsewhere in this book, but it is worth reviewing here the main elements of Quaternary environmental change that are critical for understanding humans and the environment. The Quaternary is formally classified as a system or period within the long-­term geological sequence of the Earth’s history, following on from the preceding Neogene (Gibbard et  al.  2010). The formal definition of the onset of the Quaternary is based on marine records that are now uplifted near the Sicilian town of Gela and show the first clear evidence for the onset of glaciation within the fauna and makeup of the marine sediments. The base of the Gelassian stage was thus defined as the base of the Quaternary (Gibbard et al. 2010). For reasons that are, in part, historical, most of the Quaternary is covered by the Pleistocene epoch, consisting of glacial and interglacial stages. The most recent interglacial stage, the Holocene is, however, defined as a separate epoch. The term Holocene means ‘recent’ and the only real justification for the Holocene to retain this status is that it is also associated with the rise of agricultural and later complex human societies. It is worth noting that there is widespread debate regarding the concept of the Anthropocene and its formal recognition as a geological period where humans are a critical agent of processes that will enter the geological record (e.g. Maslin and Lewis  2015). One could argue that both terms essentially define the same thing  – the geological period when humans became a significant force for environmental change and that the simplest resolution to the Anthropocene debate is to rename the Holocene. It is my personal preference but not always popular. Long-­term and more abrupt changes in Quaternary environments are driven by external drivers that essentially change the amount and distribution of energy in the system and internal feedback mechanisms within the climate system of the Earth. The former includes long-­term variations in the shape of the orbit of the Earth around the sun (Ruddiman  2003), variable solar activity (Martin-­Puertas et al. 2012), and the influence of volcanic aerosols in the upper atmosphere (Robock  2000). Feedback mechanisms within the Earth’s climate system are complex, and their

exact implications are the subject of considerable scientific enquiry, but key elements that are thought to play a role are changes in ocean circulation patterns, especially in the polar regions, changes in the strength of monsoon systems and other major air-­masses, and shifts in the drawdown or release of greenhouse gasses (CH4 and CO2). It is also important to note that without feedback mechanisms it is unlikely that these extrinsic forcing factors would have been so significant. These long-­term changes have been known for some time and featured in the previous section of this book. However, the last two decades have seen significant enhancement in the number of records of long-­ term environmental change and their response to these long-­term forcing mechanisms. There is significant new data on key areas of human habitation, such as the Asian Monsoon belt (e.g. Zhang et al. 2019), as well as much better integrated long marine and ice core records. These cover ice volume, temperature, and greenhouse gas concentrations for multiple glacial and interglacial cycles (e.g. EPICA Community Members  2004; Lisiecki and Raymo 2005). The pattern of orbital climate change is subdivided into Marine Isotope Stages (MIS), with odd stages being mostly assigned as interglacials (apart from MIS3 and some of MIS5) and even stages being glacials (Lisiecki and Raymo 2005). Critical to some of the points discussed below, a brief description of the MIS cycles for the latter part of the Quaternary is needed. The current interglacial is MIS1, the last glacial covers MIS2-­5, and the last interglacial is MIS5e, after which MIS6 is a full glacial and MIS7 a complex multi-­stage interglacial. Superimposed on these long-­term cycles of climate change are abrupt climatic events, some that last a few hundred years and others that are several thousands of years long, but where the transition between events can be as rapid as a year to a few decades (Steffensen et al. 2008). During the last glacial period (~11 700–119 000 years ago (Before Present [BP] hereafter); Rasmussen et  al.  2014), these abrupt cycles of warming and cooling have been identified in multiple Greenland ice cores and have been designated as Greenland stadials or interstadials (GS and GI). There are 26 GS/GI events recorded in the composite GICC05 chronology for the Greenland ice cores (Rasmussen et  al.  2014), revealing the complex climatic instability in this period. These abrupt changes are thought to be partly driven by the interaction between the growth and retreat of large ice sheets, producing mass ice rafting events (Rasmussen et al. 2003) that induce significant cooling in mid to high latitudes although this is best understood for the Northern Hemisphere. The most severe cooling in the high latitudes of the northern hemisphere coincides with mass iceberg discharges known as Heinrich events and have become known as Heinrich stadials (Zarriess

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et al. 2011). There is also good evidence from the Northern Hemisphere that these cycles are linked, in part, to changes to major air masses and precipitation regimes in lower latitudes, often revealed through high-­resolution speleothem archives (e.g. Nguyen et al. 2020). The expression of unstable climate in the last glacial in the Southern Hemisphere has also been refined in the last two decades and indicates a consistent out-­of-­phase relationship between warming and cooling in both hemispheres known as the bi-­polar seesaw (WAIS Divide Project Members  2015). This also gives a key to the potential drivers of these cycles, and they are thought to relate to variations in ocean circulation patterns around the globe changing the distribution of warmer and cooler surface currents, which, through heat exchange with the atmosphere, influence the wider climate. The influence of large ice sheets on ocean circulation wanes after the early Holocene (~8200 BP); however, variability across a number of climate forcing parameters has caused both long-­term and abrupt changes in different regions across the globe that may have impacted past cultures. These include changes to orbital parameters across the Holocene, particularly a weakening in insolation in the Northern Hemisphere high latitudes, variability in solar activity including periods of Grand Solar Minima, volcanic forcing, and the interaction between dominant patterns of climate known as climate modes – for example, the North Atlantic Oscillation, or the El-­Nino Southern Oscillation (Hernández et al. 2020). Together these mean that across the Holocene, there is evidence for abrupt changes in temperature or precipitation that are of lower amplitude than those witnessed in the last glacial, but that may still have had significant impacts on human societies.

­ he Impact of Climate Change T on Human Evolution and Dispersal As outlined above, the pattern of climate change that defines the Quaternary is characterized by glacial and interglacial cycles. Since the last edition of this book, there have been significant advances in understanding how orbital cycles interact with natural feedback systems, such as air masses, ocean circulation, and glacial sediments, to control the climate of the planet in the Quaternary (Tzedakis et al. 2017). From an archaeological perspective, the availability of long records of climate change that include glacial/interglacial cycles (Lisiecki and Raymo  2005), North African aridity indices (e.g. Grant et  al.  2017), and the strength of the Asian Summer Monsoon (e.g. Zhang et  al.  2019) has led to considerable interest in the role of climate change in understanding the evolution and dispersal of our genus and species. While

this is a continuation of research areas in twentieth-­century archaeology, the quality of the available climate records, along with better dating of the archaeological record, has allowed much more detailed questions to be addressed. Perhaps the most fundamental of these are: i)  did climate change drive the long-­term evolution of our genus, ii)  did it also drive or at least facilitate the dispersal of Homo sapiens out of Africa, and iii)  is it responsible for the eventual dominance of our species as the only extant member of our genus? These questions are about as fundamental as it gets, and addressing them requires integration of evidence from archaeological sites, long-­term climate archives, usually from marine and speleothem records, and local environmental records that are preserved within the landscape occupied by the hominins in question (e.g. Groucutt et al. 2021). The latter forms of environmental evidence are perhaps the most important component, as they reflect the environmental conditions experienced by humans. They are, however, often the most difficult form of evidence to compile, as they are often short-­lived and scattered across the landscape. Nevertheless, in recent years our understanding of these questions has moved on significantly. For example, there has been a consistent development of the idea that gradually increasing aridity in Africa from ~4  ­million years ago, along with episodes of wetting and drying, played a role in key aspects of the evolution of our genus (e.g. deMenocal  2011), particularly in the last ~1 ­million years (Lupien et al. 2021). One area that has seen particular attention over the last two decades is the potential role of climate change on human dispersal, expansion, and contraction. This includes the timing and number of dispersals of early modern humans out of Africa, contraction into southern refugia of Neanderthal populations during cold Heinrich stadials, and the eventual successful global dispersal of anatomically modern humans. While these processes have not all been completely linked to climate change, it has often been seen as a potentially critical factor. In some cases, the link to climate change is clear, for example during the coldest conditions during the last glacial much of Northern Europe was either under ice or in periglacial conditions (Klein et  al.  2021), while at the same time middle Palaeolithic artefacts and in some cases human remains suggest a concentration of Neanderthal occupation in the south (e.g. Jennings et al. 2011). In other cases, as discussed below, the link between climate change and population expansion or contraction is much debated. One of the most contentious debates in Palaeolithic archaeology has been around the timing and climatic

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context of human dispersal out of Africa and into the Levant and beyond. Over the last two decades, there has been an ongoing discussion over a hypothesis, partly based on genetic chronologies, for one successful human dispersal around 60–70 000 years ago (e.g. Forster  2004). This contrasts with archaeological evidence that placed the first modern human presence in the Levant much earlier, at >100 000 years ago (Grün et  al.  2005). The timing of the dispersal led some to argue for a ‘Weak Garden of Eden’ model (e.g. Rampino and Ambrose 2000), whereby an initial dispersal of early modern humans was ultimately unsuccessful due to a climate-­induced catastrophic genetic bottleneck. This is because around this time there is clear evidence, from multiple archives, for a cooling episode, which in the GICC05 chronology covers ~72 300–74 100 years ago. This is very close in time to the age of one of the largest volcanic eruptions in the Quaternary, the Younger Toba Tuff (YTT; Mark et al. (2014)). In the ‘Weak Garden of Eden’ model, a global volcanic winter caused by this eruption ended earlier out of Africa dispersals, and only the dispersal after this time was successful. The debate around this model has formed two distinct themes. The first of these is an attempt by several researchers to test the evidence for this model in the environments that humans inhabited. This is because, while the YTT was a very large eruption (e.g. Bourne et al. 2016), the climatic impacts of large volcanic eruptions tend to be short-­lived (Robock 2000), and certainly not the two thousand years of cooling seen in the ice core record. Moreover, while acidity spikes in the ice core record have been recognized around the time of the YTT (Svensson et al. 2020), no tephra from the YTT has been found in ice cores from either pole. Thus, the ‘smoking gun’ of eruption followed by long-­term cooling has been hard to find. Some archaeologists have tried to test this theory by analyzing the archaeological record above and below the YTT at sites inside and outside Africa. In Africa, the YTT appears to have had no impact on archaeological populations (Smith et al. 2018) were directly tested. Importantly for challengers to the ‘Weak Garden of Eden model’, the same is true at sites in India, where stone tool technology that is argued stylistically to be made by populations dispersed from Africa does not change before and after tephra identified as the YTT (Petraglia et al. 2007). This interpretation of a limited impact of the YTT is also supported by analyzes of lacustrine palaeoclimate data from Africa around identified tephra from the YTT that shows no evidence of a major climatic impact (Lane et al. 2013). While the YTT may now not be seen by many as the cause of a genetic bottleneck in human prehistory, there is still the issue of a divergence between the archaeological record and genetic evidence for human dispersal out of

Africa. Here is perhaps one of the most fascinating periods of human prehistory where climate change may play a role. Multiple lines of evidence from the last two decades now show that there was a clear early modern human presence outside Africa far earlier than previously thought. The earliest dated human remains come from the site of Misliya in Israel, between 194 000–177 000 years ago (Hershkovitz et al. 2018), and the presence of early modern humans has been inferred in Arabia at ~200 000 years ago, based on lithic assemblages associated with preserved lake sediments from Saudi Arabia (Groucutt et al. 2021). A similar age of 210 000 years ago has been reported on a cranium at the site Apidima in Greece, with morphological traits attributed to modern humans (Harvati et al. 2019). There is also a second, more widespread, dispersal of modern human groups into the region from as early as 127 000 years ago, in the early phases of the last interglacial, and through MIS5 (e.g. Grün et al. 2005; Armitage et al. 2011; Groucutt et al. 2018). The timing of these phases of early dispersal also indicates the role of climate change in facilitating the movement of human groups and that is because they all fall within periods of increased precipitation across the wider region, specifically the later part of the MIS7 interglacial, a wet period in MIS6, and wet periods within MIS5 (Grant et al. 2017; Groucutt et al. 2021). These longer-­term changes, driven by orbital variability, may have both allowed corridors of wetter environments to persist and facilitate human dispersal out of Africa (Breeze et  al.  2016). Indeed, at around 100 000 years ago, an early modern human group contributed to the DNA of Neanderthal populations as far away from Africa as the Altai mountains (Kuhlwilm et al. 2016). At the same time, it is possible that there were reductions in human population due to orbitally driven cooling, and in the Eastern Mediterranean, Levant, and Arabia, aridity, that followed in MIS4 (~70 000–50 000 years ago; Lisiecki and Raymo (2005)). Reanalyzes of modern human genetic data now also suggest the possibility of the start of the genetic separation between African and non-­ African populations from 100 000–120 000 years ago (Li and Durbin  2011), contributing a small proportion of DNA to some modern human groups (Pagani et al. 2016). However, several studies still suggest that the main genetically successful dispersal occurred broadly between 50 000 and 80 000 years ago (Li and Durbin 2011; Malaspinas et al. 2016; Mallick et al. 2016). The broad range of this final dispersal event is entirely consistent with a major global population decline driven by orbital climate variability in one of the coldest parts of the last glacial; in particular, the Greenland ice core data (Rasmussen et al. 2014) show predominantly cold conditions covering 71 000–59 000 years ago, followed by highly unstable climatic conditions until 54 000 years

­Holocene Climate Change and Human Adaptatio  155

ago. In such a scenario, smaller populations of Early Modern Humans from previous dispersals did not survive, and only the final dispersal event is preserved within our own DNA. Thus, without the need for the influences of a volcanic winter, there is still the possibility that climate change did lead to early dispersals proving mostly unsuccessful. While the role of climate in the dispersal of our species is one of the most critical episodes in which climate change has been considered as a driver within Palaeolithic archaeology, it is not the only event under such scrutiny. The transition in Europe from the Middle Palaeolithic to the Upper Palaeolithic, broadly associated with the final disappearance of Neanderthals from the archaeological record of Eurasia, is a process that has captured much interest. Here climate change has also been proposed as one of many drivers. There has been some discussion of the role of another volcanic super-­eruption, this time known as the Campanian Ignimbrite, or CI, from the Campe Flegrei volcanic centre in Italy (Fedele et al. 2003). The CI is not thought to be of quite the same magnitude as the YTT, but visible ash deposits of the eruption have been found as far away from Italy as Russia (Hoffecker et al. 2016). As with the YTT, it had been thought, initially on the basis of acidity spikes in ice cores, to have interacted with the onset of a long cooling event known as Heinrich 4 (Fedele et  al.  2008) and to broadly coincide with the Middle to Upper Palaeolithic transition. Others have argued that actually niche competition with newly arriving anatomically modern human populations in the period around Heinrich 4 was a more likely driver for the disappearance of Neanderthals from the archaeological record. One key issue is the quality of the available radiocarbon record for the period, which is close to the limit of radiocarbon dating. Recent advances in radiocarbon pretreatment have suggested that both the CI and Heinrich event 4 are less likely to be a driver of extinction, since the end of Middle Palaeolithic technology at sites across Europe was time transgressive and often occurred prior to the cooling event (Higham et al. 2014). This conclusion is supported by studies that use the CI tephra not as a climate marker but as a chronostratigraphic tool, and they also suggest a time transgressive Middle to Upper Palaeolithic transition not driven by Heinrich event 4 (Lowe et al. 2012). Within Upper Palaeolithic archaeology, there are also numerous other studies of the role of climate change on human expansion and contraction. For example, the timing of modern human presence in northern high latitudes (e.g. Blockley et  al.  2006; Riede  2008; Jacobi and Higham  2009) or mountainous regions (e.g. Drucker et  al.  2012). Over the last decade, there has also been

increasing interest in the influence of environmental change on human adaptation strategies that are often thought of as refuge zones for humans during climatic downturns (e.g. Blockley et  al.  2018b; Pérez-­Díaz and López-­Sáez 2021). This includes critical questions such as the role of climate change in the early development of agriculture at the end of the last glacial and very early Holocene (e.g. Barzilai et al. 2017). A key theme through all of this research, however, has been the development of better chronological and palaeoenvironmental records to address research agendas that were already developing in twentieth-­century archaeology. In my view, an even more fundamental change has taken place in terms of the question of the role of climate change on human adaptation in the Holocene.

­ olocene Climate Change H and Human Adaptation There is an entire chapter in this book now devoted to the influence of climate change on Holocene societies (Chapter  16), and this short section is not intended to cover the same ground. However, from an archaeological perspective, the inclusion of such a chapter is important as it signifies a change in perspective amongst archaeologists studying the more recent past, where environmental explanations for societal change had become deeply unfashionable (Trigger 2006). One of the reasons for this is the recognition of the nature of climate forcing in the Holocene within a wider climate science community, at least at the regional scale. Nevertheless, there has also been a clear change in the wider archaeological community in being willing to test the role of climate in our more recent past. When doing so, however, it is important to recognize that, across the Holocene, climate drivers and the scale of climate impacts vary. In addition, the human context and the vulnerability or resilience of a community may depend as much on the economic and social organization of society as on the nature of the climatic driver. In the early Holocene, the main driver of climate change is still thought to be the interaction between oceans and ice sheets, leading to several major cooling events (e.g. Wagner et al. 2013). Comparing the impact of these types of events on human populations is an interesting case in point on the resilience or susceptibility of communities to climate forcing. One of the best known of these events occurred ~8200 years ago and is commonly known as the 8.2 ka BP event. As outlined later in this book, the 8.2 ka BP event is thought to have influenced Neolithic farming communities in Turkey (Chapter 16). It has also been proposed by Wicks

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and Mithen (2014) to have had a significant impact on hunter-­gatherer communities in the west of Scotland and potentially to have influenced population numbers through changes to birth and mortality rates through resource reduction. However, an event of similar magnitude at the onset of the Holocene appears to have had no discernible influence on early Mesolithic hunter-­gatherer communities at Star Carr in North East England (Blockley et  al.  2018a). Here resource exploitation and continuous occupation, with the building of platforms and structures, continues across ~100 years of cooling and landscape instability. As outlined in Chapter 16, there is now a greater interest in the role of climate change even in more complex societies of the Late Holocene, from the Akkadian Empire (Cullen et  al.  2000) to the Late Roman world (Büntgen et al. 2016), where the role of climate change on societies has become a key question. However, the climate events in the Holocene are much shorter in duration and of lower amplitude, and testing for their impact on human populations requires a rigorous approach to developing archaeological chronologies and comparing them to the highest resolution palaeoenvironmental archives. This can be exceedingly expensive – the Star Carr study outlined above was based on extensive radiocarbon dating, tephrochronology, palynology, and isotopic analyzes. However, without

such approaches, an important aspect of understanding drivers of change in human societies cannot be properly explored.

­Conclusions The Quaternary is a period that is defined by patterns of climate change, and it is also the geological period in which our genus and species evolved (deMenocal 2011). Climate change in the Quaternary operates both on glacial to interglacial cycles but also on shorter timescales driven by ­internal feedback mechanisms, as well as forcing agents such as solar activity and volcanic eruptions. The nature of past climate change can be reconstructed in numerous ways, from lakes to ice cores, and we are now in a position to reconstruct some of the most important climate cycles with reasonably high precision. Whilst by no means the only driver of change in the archaeological record, environmental transitions have had a key role in some critical ­episodes in our evolution and adaptation. There has in the twenty-­first century also been a resurgence of interest in examining the role of climate change in more recent ­prehistory. As outlined in this section but also in other parts of this book, teasing out the role of climate in our past is an exciting challenge for the next two decades and more.

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9 Ice Core and Marine Sediment Records of Quaternary Environmental Change J.R. McConnell, S.O. Brugger, and N.J. Chellman Division of Hydrologic Science, Desert Research Institute, Reno Northern Nevada Science Center, Reno, NV, USA

Ice core and marine sediment records provide detailed ­evidence of Quaternary environmental change and have been used widely to help place observed recent changes in a long-­term perspective (Figure 9.1), as well as to evaluate linkages between the environment and human societies. For example, long-­term records from ice and marine sediment cores have been used to investigate linkages between climate and society such as the development of agriculture under the relatively benign and stable climate of the Holocene period of the past 12 000 years  – developments that probably would not have occurred or been delayed under the extreme and highly variable climate that marked the transition from the last Glacial period before it. Conversely, early human activities such as mining and metallurgy released heavy metals and other pollutants to the atmosphere, so well-­dated palaeoenvironmental records developed from ice cores have been used as year-­ by-­year indicators or proxies of industrial and economic activity thousands of years ago, allowing investigation of the vulnerability of those early societies to external shocks such as plagues, social unrest, and climate variations. While records from both the glaciochemical and marine sediment archives typically reflect large-­scale (regional to global-­scale) changes, each type of archive has advantages and disadvantages. In general, ice core records have higher time resolution and are, in most senses, more direct archives of important palaeoenvironmental parameters such as atmospheric and precipitation chemistry, hydroclimate, explosive volcanism, and during the past few millennia, industrial pollution. However, the ice core  records generally are shorter in time than marine sediment records – the longest contiguous ice core record currently extends only to 800 ka (1000 years)  – and are geographically limited to high alpine settings and the  polar regions (Figure  9.2). Recent advances in

measurement technologies and analytical protocols have revolutionized ice core research, resulting in rapid development of high-­time-­resolution, replicated records of a broad spectrum of environmental proxies, all with more accurate and reliable chronologies and often linked to proxies from other environmental archives such as those from tree-­ring and speleothem records. Marine sediment cores, conversely, often span much longer time periods (up to 200 Ma [million years]) and are more geographically distributed (Figure  9.2), but temporal resolution generally is lower, and relationships between the climate proxies and environmental change are less direct than for  ice core records. As with some peat, lake sediment (Rey et  al.  2019), and ice cores, marine sediment cores sometimes are collected near shore and close to archaeological sites. Here we describe these two palaeoenvironmental archives and how they are used, with a focus on past and possible future uses by archaeologists and historians. The descriptions include: i)  components of each archive, ii)  how they form, iii)  how they are sampled, iv)  how they are analyzed, v)  limitations and caveats of the records from these archives, and vi)  some future research directions. The ice core section is relatively comprehensive, while the marine sediment core section should be considered only a summary of a very extensive discipline, with attention focused on concepts particularly relevant for archaeological timescales. Throughout are examples of how ice-­core and marine-­sediment records have been used particularly for archaeological and historical studies.

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

Ice Core and Marine Sediment Records of Quaternary Environmental Change 3

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Figure 9.1  Marine sediment and ice core records of Quaternary environmental change. (a) LR04 globally distributed, marine benthic oxygen isotope stack. Source: Adapted from Lisiecki and Raymo (2005). (b) EPICA DOME C (EDC) carbon dioxide concentration. Source: Adapted from Bereiter et al. (2015). (c) Methane concentration. Source: Adapted from Loulergue et al. (2008). (d) Stable water isotope ratio. Source: Adapted from Jouzel et al. (2007). (e) Continental dust flux. Source: Adapted from Lambert et al. (2008).

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Figure 9.2  Map showing locations of LR04 marine sediment cores and selected ice cores. Source: Adapted from Lisiecki and Raymo (2005).

­Ice Core Records Components of the Glaciochemical Archive The cryosphere includes those parts of Earth where water is frozen, such as: i)  the two great ice sheets in Greenland and Antarctica, ii)  glaciers and ice caps located in polar and alpine regions,

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iii)  semi-­permanent alpine snow and ice patches, iv)  seasonal snow cover, v)  permafrost, and vi)  annual and multiyear sea and lake ice. Potential glaciochemical proxies of past environmental change are contained in all these components of the cryosphere, albeit for different time periods ranging from a few months to years for samples from seasonal snow covers,

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­Ice Core Record 

lake surface ice, and sea ice, to millions of years for samples from the Antarctic ice sheet. The longest continuous palaeoenvironmental ice core record extending from present to >800 000 years BP is from Dome Concordia (Dome C, EDC) in East Antarctica (Jouzel et al. 2007) (Figure 9.2), but isolated pockets of much older, discontiguous ice have been reported recently (Yan et  al.  2019). Studies of past environments generally focus on samples extracted from glaciers, ice caps, and ice sheets, although some studies have been based on samples from permafrost ice wedges (Opel et al. 2017) and semi-­permanent alpine snow and ice patches (Odegard et  al.  2017; Chellman et  al.  2020). Past environmental information is archived in the ice in many forms and can be divided into three basic categories (Figure 9.3): i)  water isotopic ratios in the ice reflect past site temperature and precipitation, atmospheric transport, and moisture source characteristics, ii)  impurities incorporated in the ice and generally ­associated with aerosols that are minute particles and droplets from terrestrial and oceanic emissions to the atmosphere (e.g. from sea spray, aeolian mineral dust, biomass burning, volcanism, industrial pollution), and

Falling snow

Ice Core

Surface layer

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iii)  air bubbles trapped in the ice that are actual samples of ancient atmospheres (e.g. greenhouse gases such as carbon dioxide and methane). Physical parameters in ice cores are routinely used in paleoenvironmental studies, but not discussed further here. These include visual patterns such as seasonal changes in bubbles and snow grain structures that, like tree rings, provide sometimes clear annual variations that can be used for annual layer counting and record dating such as in the iconic GISP2 ice core (Alley et al. 1997). In addition, the frequency and severity of surface melting and the subsequent melt layers preserved in the ice core record have been used as a proxy of maximum summer temperature. Such records, together with meteorological modelling, recently have been used to document pronounced summer warming in Greenland since ~1950 (Trusel et al. 2018).

Forming the Glaciochemical Archive Higher elevation regions of active glaciers and ice sheets are called accumulation zones. This is where the surface mass balance is positive (i.e. precipitation falling as snow exceeds melting and sublimation) so each year layers of

Seasonal Water isotopes Sea spray Dust Pollutants

Firn (old snow), with trapped air

Isochrone

Radioactive fallout

Firn to ice transition 60 – 110 m

Isochrone

Cosmic ray burst CO2 CO CH4

Ice with gas bubbles 2000 – 2500 m Isochrone

Volcanic sulfur Volcanic tephra

Figure 9.3  Schematic of the surface of ice sheets and glaciers. Snow accumulates over time and is converted to ice between 60 and 110 m below the surface. Impurities associated with aerosols including continental dust, sea spray, volcanic and biomass burning fallout, and during recent periods, anthropogenic pollutants are incorporated in the snow. Along with the stable isotopic composition of the snow itself, many impurities are seasonally varying and enable identification and counting of annual layers that underpin independent dating of the paleoenvironmental record. Fallout from large explosive eruptions, atmospheric thermonuclear testing, and cosmic ray bursts that generate short-­lived increases in cosmogenic nuclides create occasional isochrones that can be used to synchronize between ice core records and between ice core and other paleoenvironmental records such as those from tree ring, lake, and peat sediment cores. Trapping of ancient air in bubbles within the ice occurs at the firn to ice transition, so there is a sometimes large (thousands of years) offset in age between the records of atmospheric gases and the ice impurity and water isotope records of past precipitation chemistry and climate.

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snow are accumulated and preserved at the surface (Figure 9.3). The lower elevation regions where the surface mass balance is negative are called ablation zones. In active glaciers and ice sheets, ice flows from the accumulation zones to the ablation zones. The boundary between the accumulation and ablation zones where surface mass balance is near zero is called the equilibrium line altitude (ELA) and often is used as a climate change indicator. If the ELA rises as a result of climate warming, the accumulation zone shrinks, and the ablation zone initially expands, leading to a mass imbalance, a reduction in ice flow, and ultimately to a reduction in the size or retreat of the glacier. Snow falling and accumulating at the surface of a glacier or ice sheet is highly porous, with a density of just 50–70 kg/ m3 for dry snow and 100–200 kg/m3 for wet snow. As the snow ages, its density increases. Older, aged snow is referred to as firn and its near-­surface density is about 300 kg/m3. As the firn layers are buried, they are compressed by the weight of the overlying snow with the density increasing from ~300 to >800 kg/m3 (Figure  9.3). At about 80–110 m depth at cold sites where the surface melt is rare (depending on the site characteristics such as snow accumulation rate and temperature), the snow is compressed to ice, and the pore spaces between snow grains seal off to form gas bubbles that trap samples of the ancient atmosphere and reflect atmospheric concentrations at the time of pore close off. The density of glacier ice ranges from 830 to 917 kg/m3 depending on the air bubble content. While most deep ice cores have been collected from topographic ridges or domes on ice caps and ice sheets where net ice flow is mainly vertical, more recently, some deep and intermediate cores on the ice sheets, as well as many cores from high-­alpine glaciers, have been collected at flank sites where horizontal flow rates can be significant. Horizontal flow means that the point at the surface where the snow accumulated moves progressively further and further upstream of the drilling location with increasing depth. When interpreting such ice core records, the location at the surface where the snow was deposited is important because depositional processes may be significantly different 10 or 20 km upstream than at the drilling site. Water Isotopes

Past climate  – specifically proxies of site temperature, moisture source characteristics (e.g. ocean surface temperature, relative humidity), and atmospheric circulation – is recorded in the isotopic ratios of hydrogen and oxygen preserved as ice in the accumulation zones, with the shallowest layers representing the most recent past. These iconic records document large changes in past climate (Figure 9.1) such as during glacial/interglacial timescales (Lorius

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et al. 1990; Jouzel et al. 2007), as well as important but less severe changes during the relatively stable Holocene climate that have played a crucial role in human history (Masson et  al.  2000), i.e. such as the Medieval Climate Anomaly and Little Ice Age. These climate reconstructions are based on the stable isotopes  – a term which refers to atoms of the same element with different atomic weights – of water molecules in the ice. The water molecule contains one oxygen and two hydrogen atoms, but there are several isotopes of oxygen and hydrogen that exist naturally on earth. The most common water isotopic ratios measured in ice cores are δ18O, which refers to the ratio of oxygen atoms with atomic masses of 18 and 16, and δ2H (often presented as δD), which refers to the ratio of hydrogen atoms with atomic masses of 1 and 2 (2H is also known as deuterium, D). Because water molecules comprised of different combinations of these isotopes have slightly different masses, they behave differently during physical processes, such as evaporation and condensation called mass-­dependent fractionation. Thus, the isotopic composition of water, and  therefore precipitation, is somewhat temperature-­ dependent. This temperature dependence can be quantified and used to calibrate the water isotopic record from an ice core to a proxy of site temperature. Water isotopes also provide records of long-­term changes in the global hydrologic cycle. For example, water removed from the oceans and stored on land as glaciers and ice sheets lowers the sea level but also changes the isotopic characteristics of the remaining water in the ocean; water evaporated over the oceans and deposited on the ice sheets will reflect the isotopic characteristics of the ocean-­water reservoir at the time. Aerosols

In addition to past environmental change recorded in the  isotopic ratios of the ice, impurities linked to past ­climate and atmospheric chemistry also are preserved in the annual snow layers (Figure 9.3). These impurities often are associated with aerosols that consist of minute particles and liquid droplets arising from emissions to the atmosphere from sources such as sea spray, desert dust, quiescent and explosive volcanism, forest fires, marine, and terrestrial biogenic emissions, as well as industrial and other anthropogenic emission sources during recent times (Figure  9.4). Aerosols can be deposited from the atmosphere through a dry or wet deposition. In the former, aerosols are deposited between precipitation events through gravitational settling or when filtered by near-­ surface snow as winds move air across the snow surface and through the top few centimetres of the snow in a ­process called wind pumping (Harder et  al.  1996,  2000). In the latter, aerosols are incorporated in precipitation as

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163

Atmospheric Aerosol Sources

Extraterrestrial dust

Marine aerosol (n < 103 ml–1)

Sinks

Continental aerosol (n~103 –105 ml–1) Volcanoes

Gas-to-particle reactions

Precipitation scavenging

Sulfate CCN SO2 Wind

Sea DMS spray

In-cloud scavenging - Nucleation - Brownian diffusion - Phoresis

Forest fires

- Impaction - Brownian diffusion - Phoresis

Dry deposition

Industry Autos

Wind Vegetation erosion and resuspension

Wet deposition

Figure 9.4  Schematic of primary aerosol sources and sinks. Source: Credit NOAA.

insoluble particles or as dissolved ions in the ice matrix and in the quasi-­liquid layer between snow grains. A number of processes can alter ice core chemical and isotopic records. These include: i)  wind redistribution or removal (scouring) of snow at the surface before burial, ii)  surface melting, percolation, and refreezing deeper in the snow pack, and iii)  surface melting and runoff. The second moves impurities vertically in ice core c­ hemical records and the third reduces overall impurity concentrations in the snow and eventually preserved in the ice core record. Surface melting primarily occurs at warmer sites such as low-­elevation polar locations or alpine drilling sites in the mid-­ and low-­latitudes, complicating interpretation. Additional post-­depositional changes in ice core records result from diffusion of water isotopes and more volatile chemical species, with most of the diffusion occurring through gas-­phase diffusion before the porous firn becomes ice. Diffusion is a temperature-­dependent process that smooths the chemical and isotopic record; its effects are enhanced at relatively warm ice core sites. While many chemicals and most insoluble particles remain in the snow once deposited (irreversibly deposited), more volatile chemical species such as hydrogen peroxide and some compounds of organic carbon, nitrogen, and mercury exchange between the atmosphere and snow reservoirs during burial (reversibly deposited). The process of

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reversible deposition (Figure 9.5) continues as long as the air in the snowpack is able to interact with the air above the snow surface. Because diffusion controls the rate of chemical movement into and out of the snow grains, the impact of reversible deposition on the preserved chemical record is greatest at warm, low-­snowfall sites and smallest at cold, high-­snowfall sites. Reversible deposition changes the relationships between impurity concentrations in precipitation and what is preserved in the ice, making the interpretation of ice core records as palaeoenvironmental proxies more difficult. Gases

Gas records are extracted from minute air bubbles in the ice, and so many compounds provide a direct sample of ancient atmospheres including greenhouse gas (GHG) records that are cornerstones of climate change research (Lorius et  al.  1990). Frequently extracted records include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These three gases absorb outgoing thermal radiation in Earth’s atmosphere, thereby warming the planet (i.e. the greenhouse effect). Reconstructing past atmospheric concentrations, and controls on GHG concentrations, is critical to understanding the climate system – including how human activities have affected the past climate and how they will affect future climate. Noble gases also are measured in ice cores and used to study a range of palaeoenvironmental issues such as past changes in temperature at local to regional scales near the

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Snowfall

Wet and dry chemical deposition

Figure 9.5  Reversible chemical deposition. Some fraction of more volatile compounds deposited in snow may be emitted back to the atmosphere during burial while the snow still is in contact with the atmosphere. Isotopic fractionation may also occur. These processes will alter the paleoenvironmental record before it is preserved in ice.

Fraction of original chemical deposition reemitted Snow Surface Firn

Circulating air High net snowfall = high preservation in ice Low net snowfall = low preservation in ice

Density increasing Permeability decreasing Light penetration decreasing Ice

ice core site based on differential temperature-­dependent thermal diffusion within the firn column prior to pore close-­off (Severinghaus et  al.  1998), and also at global scales based on temperature-­dependent solubility in the oceans (Headly and Severinghaus  2007; Bereiter et  al.  2018). As measurement technology develops and process-­level understanding improves, isotopic ratios of carbon, nitrogen, oxygen, hydrogen, and other gases trapped within glaciers and ice sheets are providing additional information on emission sources, e.g. distinguishing between wetland, biomass-­burning, and fossil-­fuel sources of CH4 (Schaefer et al. 2016; Bock et al. 2017). Note that for various reasons, reliable gas records generally can be obtained only from cold, dry-­snow-­zone drilling sites such as those at higher elevations on the Greenland and Antarctic ice sheets. Unlike aerosol and water isotope records that reflect the environmental and atmospheric chemistry conditions at the time the snow accumulated and was buried, gas records reflect the atmospheric condition at the time of pore close-­ off (Figure 9.3) so the age of the air trapped in bubbles is younger than the surrounding ice itself. The difference in time between when the snow accumulated (ice age) and when the pore spaces seal off (gas age) is called the delta age. The pores spaces progressively seal off over a range of depth referred to as the lock in zone (LIZ) that often is a few metres thick, so the delta age has a range associated with it (Bender et al. 1997). For many of the deep ice cores from cold, moderately high snowfall sites such as GISP2, NGRIP, and NEEM in Greenland or WAIS Divide in Antarctica (Figure 9.2), the Holocene delta age is roughly 200–300 years with relatively low uncertainty (Schwander et  al.  1993). At sites with very high snow accumulation rates such as Law Dome in Antarctica, the delta age is only about 70 years making cores from Law Dome ideal for studying recent anthropogenic changes in atmospheric gases such as CO2 and CH4 (Etheridge et  al.  1998). Conversely, at very low snowfall sites such as those on the East Antarctic Plateau (Figure  9.2), delta age typically is

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thousands of years (Bender et al. 1997) and can range from 1000 to >10 000 years, particularly at flank drilling sites because of past changes in snowfall rates and temperature along the flow path represented by the ice core record (Menking et  al.  2019). Uncertainty in delta age hinders synchronization of aerosol and water isotope records with gas records even from the same ice core, thereby limiting interpretation (Buizert et al. 2015b, 2018). Note that it generally is not possible to obtain reliable gas records from alpine cores.

Sampling and Analysing the Glaciochemical Archive Samples have been collected from glaciers and ice sheets for many decades for palaeoenvironmental studies, including as part of exploration of the Greenland ice sheet in the early twentieth century when shafts were dug by hand deep vertically into the ice sheet to study firn stratigraphy and obtain samples (Gertner 2019). Some of the earliest ice coring was conducted at Camp Century in northwest Greenland when the effort to drill an approximately 1.35 km core to the bedrock beneath the ice sheet was completed in July 1966 (Dansgaard et al. 1969). Ice Core Drilling

Ice cores usually are drilled vertically in the accumulation zones of ice sheets and glaciers since the objective is to obtain well-­dated, continuous paleoenvironmental records (Figure  9.3). Drilling operations can be divided roughly into three different depth ranges based on the effort required to complete the drilling and the length of the paleoenvironmental record recovered: i)  shallow drilling from ~10 to ~50 m depths that can be completed in a few hours to a few days, yielding environmental records extending over recent years to decades, ii)  intermediate drilling to depths of ~50 to ~400 m that can be accomplished in a few days to a few months

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­Ice Core Record 

but generally are completed within one field season, yielding records extending from decades to ­millennia, and iii)  deep drilling to depths from ~400 m to more than 3400 m and often to bedrock, generally requiring multiple field seasons and substantial infrastructure, but yielding continuous paleoenvironmental records extending from millennia to >800 000 years. An important distinction between these different types of drilling is that shallow and intermediate drilling often can be accomplished without the use of drilling fluid (i.e. dry drilling). For deeper drilling, however, ice flow results in closure of the borehole with time so drilling fluid (i.e. wet drilling) must be used to counteract the closure. Drilling fluid generally consists of an organic fluid with an added densifier to achieve the correct density to keep the borehole open. Drilling fluid can be a source of contamination for some chemical species and elements that are of paleoenvironmental interest, however, requiring robust sample decontamination procedures to ensure reliable records from wet-­drilled cores. Ice cores usually are collected using electromechanical drills that use spinning cutters to cut through the ice but are occasionally recovered using thermal drills that melt their way through the ice. With the objective of extracting consecutive cylinders of ice for chemical and other analyses, cores typically are drilled in 1–3 m sections, and the drill returned to the surface to extract the ice samples between sections (Figure 9.6). The cores are processed in the field and later in the laboratory with the aim of assembling a continuous cylinder of firn and ice extending from the surface to the bottom of the borehole. This cylinder is then sampled to provide a reliable, well-­dated record.

165

Ice Core Analyses Ice cores typically are analyzed for a broad range of isotopic ratios, chemical and elemental concentrations, and other properties, with the range of the measurements and sample resolutions determined by the objectives, scope, and budget of the research project. Traditional ice core studies were based on the analysis of discrete samples. More recently, continuous systems based on ice core melter systems and measurements of contiguous longitudinal samples have revolutionized ice core analyses by enabling rapid development of high-­depth-­resolution palaeoenvironmental records for a range of water isotopes, aerosols, and even some gases with substantially lower effort and far lower costs than traditional discrete analyses. Discrete Measurements

In discrete analyses, multiple samples representing specific depth ranges are cut from each cylindrical ice core either spaced out or contiguously along the core, and subsequently melted and analyzed individually. Because the outsides of the samples are potentially contaminated during drilling, cutting, and handling, the samples first must be decontaminated by removing the outer layers, which is accomplished either through mechanical means (e.g. scraping – Hong et al. 1994) or by rinsing with ultra-­pure water. Decontamination is less important for parameters that are less susceptible to contamination either because of relatively high concentrations in the ice (e.g. sulfur) and/or because the substance is not common in the laboratory (e.g. radionuclides). Contamination generally is not a concern for water isotope measurements and gases. However, effective decontamination is critical for parameters such as lead that occur in pristine natural environments only at low concentrations but are common in the industrialized environment or in the laboratory (Hong et  al.  1994; McConnell et al. 2018). Continuous Measurements

Figure 9.6  A typical 100 mm diameter ice core. Source: Credit N. Chellman.

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In continuous analysis systems (also referred to as continuous flow analysis [CFA] systems), a single longitudinal sample from each core is analyzed using a melter system, with samples representing up to a few metres of ice often analyzed sequentially. The longitudinal samples are cut from the cylindrical cores and loaded into a vertical sample holder. The ice samples fall by gravity onto a heated plate referred to as a melter head, with meltwater from two or three different regions of the sample cross section separated into different flow streams by engraved grooves in the melter head. These different meltwater streams are pumped to a range of analytical systems for near-­real-­time chemical, isotopic, and other measurements, as well as to fraction

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collectors to obtain sequential meltwater samples for offline measurements or for archiving. Sample decontamination is achieved by analyzing only the innermost meltwater streams and the potentially contaminated outermost meltwater discarded. For example, in the continuous analytical system at the Desert Research Institute (DRI) in Reno, Nevada, United States (McConnell et al. 2002, 2017), the meltwater is split on the melter head into three regions with: i)  the innermost 10% of the cross-­section (and so least likely to be contaminated) used for extremely low level (e.g. picogram/gram to femtogram/gram) elemental measurements, ii)  the next 20% for measurements of water isotopes and the more abundant impurities such as nitrate, ammonium, and black carbon, and iii)  the outer-­most 70% of the cross-­section either captured for bulk measurements of difficult-­to-­contaminate impurities such as cosmogenic nuclides that require large sample volumes or discarded as potentially contaminated. Gases with low solubilities such as CH4 and carbon ­ onoxide also can be measured using these continuous m methods, often simultaneously with aerosol-­related ­concentrations and water isotope ratios (e.g. Rhodes et al. 2015). The meltwater stream coming from the melter head is a combination of water and air from the bubbles in the ice, so the air must be separated from the water prior to gas analyses. Such simultaneous measurements substantially reduce the amount of ice consumed by each individual measurement (Rhodes et  al.  2013,  2015; Fain et al. 2014), thereby greatly increasing the scope and temporal resolution of palaeoenvironmental information that can be obtained from an ice core and at much lower cost because of reduced sample handling and decontamination efforts. However, gases with high water solubilities such as CO2 are difficult or impossible to measure accurately with melter-­based continuous methods.

Analytical Techniques Below is a brief introduction to different measurement methods typically used to analyze ice core samples for water isotope ratios, aerosols-­related elements, chemical species, and gases. Water Isotope Ratio Measurements

Contamination is unlikely so discrete samples are melted in sealed containers to minimize evaporation and then analyzed for hydrogen and oxygen isotope ratios using either isotope ratio mass spectrometry (IRMS) (Muccio and

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Jackson  2009) or cavity ring-­down spectroscopy (CRDS), which measures isotopes using infrared absorption spectroscopy. For melter-­based, continuous-­flow analytical systems, only CRDS can be used (Gkinis et al. 2010; Maselli et al. 2013). Aerosol Measurements

After decontamination, discrete samples generally are melted in precleaned plastic containers and then analyzed using a broad range of analytical techniques and instruments. For example, the major ions (e.g. sodium, magnesium, sulfate, chloride, potassium, nitrate, ammonium) traditionally are analyzed using ion chromatography (IC) (Morganti et al. 2007). Heavy metals are analyzed using graphite furnace atomic absorption (GFAAS) (Hong et al. 1994, 1996), inductively coupled plasma mass spectrometry (ICP-­MS) (McConnell et al. 2002; Osterberg et al. 2008), or thermal ionization mass spectrometry (TIMS) (Rosman et al. 1997; Vallelonga et  al.  2002). For continuous flow analysis ­systems, fluorescence spectroscopy often is used for chemical species such as hydrogen peroxide and ammonium, and  absorption spectroscopy for species such as nitrate (Kaufmann et  al.  2008), although pseudo-­continuous IC-­based techniques recently have been developed (Morganti et al. 2007). In a few advanced ice core laboratories, a broad range of elements from sodium-­23 to plutonium-­239 is measured continuously using ICP-­MS (McConnell et  al.  2002,  2017), including sulfur-­34 and lead-­208, which are of particular interest in archaeological and historical studies (Sigl et  al.  2015; McConnell et  al.  2018,  2019). Black carbon (i.e. soot) concentrations and size distributions can be measured using laser-­based, single particle incandescence techniques (McConnell et al. 2007). Continental dust particle concentrations and size distributions can be measured in continuous flow systems using semiquantitative, laser-­based particle counters (Ruth et al. 2003) and in discrete samples using a Coulter counter that is based on resistive pulse sensing. Mineral acidity can be measured directly in the meltwater using titration techniques or pH probes but only after compensating for laboratory CO2 levels (Pasteris et  al.  2012). Non-­destructive methods for measuring proxies of mineral acidity on ice include electrical conductivity (ECM) (Wolff et al. 1997) and dielectric profiling (DEP) (Wilhelms 2005). Gas Measurements

Measurements in ice cores of a broad range of stable atmospheric gases require a range of analytical techniques such as IRMS, gas chromatography, and infrared laser spectroscopy. The first step in ice core studies is to extract the gas, which can be challenging. Extraction is accomplished by melting (wet extraction) or by crushing (dry extraction)

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­Ice Core Record 

discrete ice samples under a vacuum. A hybrid wet technique called melt-­refreeze involves repeatedly melting and refreezing discrete samples under a vacuum to fully extract the gas (e.g. Ryu et  al.  2018). Compounds with relatively high water solubilities including CO2 and N2O, or those that may be altered by chemical or biological processes in meltwater, require dry extraction (e.g. Ahn et  al.  2009). Conversely, those with relatively low solubilities such as CH4 and carbon monoxide can be measured with wet extraction techniques. For continuous melter systems, measurements of CH4 (Rhodes et  al.  2015) and carbon monoxide (Fain et al. 2014) are done with cavity ring-­down spectroscopy (CRDS). Pseudo-­continuous methods based on gas chromatography also have been used for CH4 (Schupbach et al. 2009).

Limitations and Caveats Although ice cores provide detailed and arguably the most direct palaeoenvironmental records from natural archives, they are not without limitations. Here we discuss some of the most important limitations and caveats of ice core records with relevance to their use in archaeological and historical studies. Ice Core Chronologies

Chronology development, or dating, is an interpretation of the original ice core chemical and other measurements made in depth. Establishing accurate, robust chronologies – including understanding and quantifying uncertainties – is among the most important, difficult, and controversial aspects of ice core and other paleoenvironmental research. Moreover, as new analytical techniques are developed and more independently dated, high-­resolution ice core records become available, chronologies for earlier ice core records may change (Sigl et  al.  2015; Chellman et  al.  2017). Accurate dating particularly is important when comparing environmental records from different sources (e.g. ice core volcanic records to tree-­ring growing-­season temperatures), and also with historical documents. Independent, objective dating is crucial if inferring causality between past societal events such as the advent of plague pandemics and declines in ancient economies (e.g. through changes in lead pollution recorded in Arctic ice cores (McConnell et al. 2018, 2019), or famine and social unrest from climate stresses resulting from explosive volcanism (McConnell et  al.  2020), for example through changes in the East African summer monsoon and the annual Nile river flood (Manning et al. 2017). In addition, many ice core, dendrochronological, and other paleoenvironmental records are dated on a year-­before-­present age scale, with present defined as 1950 Common Era (ce). Confusion may arise

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when converting this numerically continuous age scale to the Before Common Era (bce) and ce age scale often used by historians (McConnell et al. 2020). Chronology development for ice core records ideally is done through annual layer counting, where seasonal variations in multiple chemical and/or optical properties are exploited to identify and count annual markers (Figure 9.7). The most recent year of the chronology is the year in which the core was drilled. Many parameters measured in ice show pronounced seasonal variations linked both to changes in the magnitude of the emissions to the atmosphere and to changes in atmospheric transport from emission to ice core site. For example, Northern Hemisphere emissions of both sea salt and desert dust are high in winter and spring. These high emissions coincide with vigorous long-­range atmospheric transport in winter and spring, resulting in the highest concentrations of sea salt and Asian continental dust impurities in Greenland snow and  thence ice during January through April each year. Conversely, in the European Alps strong local summertime convection efficiently transports impurities to high-­elevation ice core sites resulting in ~10-­fold higher concentrations for most impurities in summer than in winter (Legrand et al. 2018). In both cases, the pronounced seasonal cycle in the ice core chemistry linked to emissions and atmospheric transport underpins annual layer counting. As with all measurements, however, there is uncertainty associated with annual layer counting, so it is important whenever possible to evaluate any new chronology against existing chronologies using markers with well-­established dates both to constrain annual layer counting and to synchronize different ice core or other palaeoclimate or palaeoenvironmental records. Widely used chronological markers (Figure 9.3) include: i)  layers of high radiation from atmospheric thermonuclear testing, ii)  short-­lived (one to two-­year) variations in cosmogenic radionuclide concentrations, and iii)  fallout from large, explosive volcanic eruptions. High levels of radioactivity in snow and ice layers resulting from extensive atmospheric thermonuclear testing in the mid-­twentieth century provide a series of chronological age markers, but only for the period when atmospheric testing occurred between 1952 and the implementation of the Limited Nuclear Test Ban Treaty in 1963. In addition, the usefulness of direct radiation measurements will be limited in future ice core and other paleoenvironmental studies because cesium-­137 (half-­life of 30.17 years) and other short-­lived radionuclides have decayed to near ­background levels after more than 50 years. Long-­lived plutonium-­239 (half-­life of 24 100 years) and other

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390.5

Depth (m) 390 389.5

389

388.5

Figure 9.7  Example of multiparameter annual layer counting in ice from the first century bce. Source: Adapted from McConnell et al. (2020).

388 300 nssS/ssNa

Year (BCE):

391

50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34

391.5

33 32 31 30 29

168

200

ssNa (ng/g)

32

100

24

0

16 8

0.015 0.01 0.005

Ce (ng/g)

0

0

10 8 6 4 2

32

0

24 16 8

nssCa (ng/g)

Mg (ng/g)

12

0 391.5

391

390.5

390 389.5 Depth (m)

389

388.5

radionuclides provide an alternative for ice, however, and  methods for extremely low-­level measurements of  plutonium concentrations (30 μm) individual tephra particles. More recently, continuous, size-­resolved measurements of insoluble particles coupled with continuous, non-­sea-­salt sulfur or acidity measurements have been used to identify invisible diffuse tephra layers, and new methods developed to geochemically fingerprint much smaller (5–10 μm) tephra particles filtered from the ice (e.g. Dunbar et  al.  2017; McConnell et  al.  2017,  2020). To identify possible source volcanoes, geochemical fingerprints of the tephra particles filtered from the ice are compared to fingerprints of reference tephra collected near source volcanoes thought to have erupted about the same time (Figure 9.8). Because of the high temporal resolution, well-­dated ice core tephra records have been used to cross-­date tephra layers found in peat bogs, lake sediments, or other paleoenvironmental archives with lower temporal resolution and larger dating uncertainties (Coulter et al. 2012). For ice cores where annual layer counting is not possible, such as those perturbed by substantial surface melt and percolation or where flow thinning has compressed the

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annual layers beyond recognition, chronological age markers from thermonuclear testing, cosmogenic radionuclides, and volcanic fallout are used to establish an approximate depth-­age scale. The chronology is then interpolated between markers and extrapolated from the deepest marker to the bottom of the core. A more sophisticated and frequently used approach is ice-­flow modelling to guide the interpolation and extrapolation (Mulvaney et  al.  2012) although extrapolations from the deepest reliable chronological age marker to the bottom of the core often are highly uncertain. Lower frequency (decadal to century-­scale) variations in ice beryllium-­10 and tree carbon-­14 also have been used to synchronize between ice core records and between ice core and tree-­ring records (Adolphi and Muscheler  2016). Ice core to tree-­ring record synchronization is particularly important for quantitative understanding and modelling of climate and climate drivers because, while tree-­ring records provide detailed records of local climate such as growing-­ season temperature or precipitation, ice core records provide high-­resolution records of potential hemispheric to global-­scale climate drivers such as the timing, magnitude, injection height, persistence and sometimes even the provenance of stratospheric sulfate aerosols from volcanic eruptions (Sigl et al. 2015). Finally, for longer records particularly those that extend into the glacial periods, rapid variations in gas concentrations (particularly CH4) and stable water isotope ratios such as those associated with glacial-­interglacial cycles and/or Dansgaard–Oeschger (D–O) events are used for synchronization between ice cores and marine sediment cores. For example, global-­scale changes in atmospheric CH4 assumed to be linked by the Southeast Asian Summer Monsoon to coeval changes in water isotope ratios in Greenland ice during D–O events recently were used to synchronize CH4 records from the West Antarctic Ice Sheet Divide (WAIS Divide) and water isotope ratio records from North Greenland Ice Core Project (NGRIP) for ice older than 30 000 years, recognizing that uncertainties in delta age at WAIS Divide since CH4 records are on a gas-­age timescale while water isotope ratio records are on an ice-­ age timescale (Buizert et  al.  2015b,  2018). In addition, assumed linkages between atmospheric CH4 and the Southeast Asian Summer Monsoon from 30 to ~66 k years before 1950 (years BP) were used to synchronize between radiometrically dated speleothems and ice core gas records (Buizert et al. 2015a). Understanding Effects of Atmospheric Transport

Many of the impurities in snow and ice used for paleoenvironmental research are associated with aerosols such as continental dust (Mahowald 2011; Delmonte et al. 2020)

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Ice Core and Marine Sediment Records of Quaternary Environmental Change

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Figure 9.8  Example of geochemical fingerprinting of tephra in ice used to identify the source of volcanic fallout. (a) Continuous records of sulfur and insoluble particle concentrations in the NGRIP2 central Greenland ice core, with the large particle spike (shaded bar) at the start of the 43 bce volcanic fallout event suggesting tephra deposition. (b) Comparison of major elements measured in tephra found in the ice with reference tephra from known first century bce eruptions clearly identifies the Okmok volcano in Alaska as the source. Measurement precision is illustrated by the red and grey crosses. Source: Adapted from McConnell et al. (2020).

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and those from biomass burning (McConnell et al. 2007) and industrial emissions (Hong et al. 1994, 1996). Unlike long-­lived, well-­mixed GHG such as CO2, aerosol concentration and deposition rates are highly variable in space and time because their atmospheric lifetimes are short (days to weeks). Moreover, the sources of many of these aerosols are in the mid and low latitudes, so long-­range atmospheric transport is implicit in creating the polar ice  archive. Quantitative interpretation of such records requires sophisticated atmospheric aerosol transport and deposition modelling to understand long-­range transport. However, such modelling requires detailed meteorological fields generally not available prior to the twentieth century, so it is often assumed in such studies that meteorology during the period of interest was similar to the twentieth century. In addition, not all aerosols will be transported in the same way since particle size, injection height, and other variables are closely related to transport. For example, relatively large (typically >30 μm) tephra from even minor explosive volcanic eruptions injected well above the atmospheric boundary layer will be transported very

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differently than 1–5 μm dust particles or lead emissions from mining and smelting operations primarily released at the surface. In a recent example (McConnell et al. 2018), the state-­ of-­the-­art atmospheric aerosol transport and deposition model FLEXPART (Stohl et al. 2005) was used to evaluate the effects of long-­range atmospheric transport on a central Greenland ice core record of lead pollution during European antiquity. Archaeological and other evidence suggested that the bulk of lead emissions during this period originated from mining and smelting operations in the southern Iberian Peninsula, so the lead had to be transported more than 4600 km through the atmosphere to the central Greenland ice core site. Because most lead ores consisted largely of galena, lead pollution was linked closely to silver production in ancient economies, and silver often was the primary component of coinage (Figure  9.9). FLEXPART modelling indicated that lead emissions of 1000  metric tons in southern Iberia would result in ~0.41 (±0.2) μg/m2/year of pollution lead deposition at the ice core site, thereby allowing quantitative

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Figure 9.9  Chronology of European lead pollution in Greenland ice during antiquity. Iberian mining and smelting were the primary sources of silver used in Roman coins that resulted in large atmospheric lead emissions and widespread pollution in the Arctic. The highly resolved ice core record provides a well-­dated (+/–2 years) proxy of Roman silver production, closely matched by independent records of the fineness of silver coinage, suggesting close linkages between the economy and plagues, wars, and social unrest. Source: Adapted from McConnell et al. (2018).

inversion of the Greenland ice core lead deposition record to an estimate of year-­by-­year atmospheric lead emissions from ancient mining and smelting operations that were compared to emissions estimates based on archaeological and historical evidence. In addition, FLEXPART simulations suggested that year-­to-­year variations in long-­range atmospheric transport alone resulted in ~60% (1σ) variations in annual lead deposition at the ice core site, providing important quantitative constraints on the historical interpretation of short-­term changes in the annually resolved ice core record. That is, a single year 60% increase or decrease in lead pollution in Greenland could result simply from year-­to-­year atmospheric transport variability and so cannot be attributed to a particular short-­term historical event. In this (McConnell et al. 2018) and a related study of medieval Arctic lead pollution (McConnell et  al.  2019), an 11-­year median filter was used to reduce the uncertainty caused by annual transport variability from 60 to ~20% while preserving any step-­function changes in lead deposition, as well as to determine uncertainty limits (Figure 9.9).

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Aerosol deposition declines approximately exponentially away from the emissions source, so even relatively small sources located close to an ice core site may have a large effect on the palaeoenvironmental record. While this is typically not a consideration for polar ice cores located far from any potential mid-­or low-­latitude emissions sources, it is of particular concern for high-­alpine ice cores located much closer to (and often surrounded by) aerosol emissions sources. For example, FLEXPART modelling (Lim et al. 2017; Preunkert et al. 2019; Legrand et al. 2020) shows that palaeoenvironmental ice records from the French and Swiss Alps, where a number of ice cores recently have been collected, are one to two orders of magnitude more sensitive to emissions sources located immediately adjacent to the Alps than to emissions from other parts of Europe (Figure 9.10). This transport behaviour means that attribution of short-­term (e.g. annual or multi-­annual) changes in European high-­alpine ice core records solely or even predominantly to changes in emissions from more distant parts of Europe (e.g. western France (Loveluck et al. 2018) or the British Isles (More et al. 2017)) is highly uncertain.

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Figure 9.10  Sensitivity of ice core records from (a) central Greenland NGRIP and (b) French Alps Col du Dome (CDD) to European atmospheric emissions based on FLEXPART aerosol transport and deposition model (Stohl et al. 2005) simulations. Source: Preunkert et al. (2019)/ with permission of John Wiley & Sons. Emissions sources close to the Alps will have one to two orders of magnitude greater effect on the CDD ice core paleoenvironmental record than similar emissions from more distant locations such as the British Isles or western France. Conversely, all European emissions will have a similar effect on distal central Greenland ice core records although with a bias to more northern and western emissions (e.g. the British Isles).

Seasonality of Net Snow Accumulation

Ice Flow and Chronology Development

Many aerosols of environmental interest are primarily wet deposited. Snowfall events are infrequent and not uniformly distributed throughout the year, so on a sub-­annual scale palaeoenvironmental records from ice archives are both discontinuous and may contain significant seasonal biases. Year-­round studies of net snow accumulation at Summit, Greenland, as well as modelling studies (Rhodes et al. 2017), indicate that the seasonal biases in net snow accumulation may be different at the various ice-­sheet divide sites where Greenland ice cores traditionally have been collected. Seasonal accumulation biases may be more significant at flank drilling sites on the polar ice sheets where katabatic (downslope) winds and surface undulations caused by ice flow over bedrock topography result in regions of snow scouring, particularly in winter and spring when katabatic winds are strongest. Moreover, the extreme seasonal scouring has been observed at high-­alpine sites such as Colle Gnifetti in the Swiss Alps, where strong winds remove winter layers. This scouring leads to a pronounced summer bias in the ice core records from the site (Sigl et al. 2009), largely eliminating consistent preservation in the snow and ice of seasonal cycles in chemistry required for annual layer counting and thus hindering precise dating of Colle Gnifetti ice core records especially prior to the 1815  ce eruption of Tambora which provides an important constraint on annual layer counting.

Glaciers are defined as flowing ice. Flow, however, distorts the internal stratigraphy and therefore the preserved palaeoenvironmental archive. In the upper 80–90% of glacier and ice-­sheet depth, ice flow often is well constrained so much of the distortion is removed through physically-­ based ice flow modelling. In the deeper parts, however, ice flow generally is not well constrained by such models leading to significant dating uncertainty. The result is that reliable palaeoenvironmental records spanning thousands or even hundreds of thousands of years can be developed from ice cores extracted from thick polar ice sheets often reaching depths of more than 3 km. Reliable palaeoenvironmental records from much thinner (one to a few hundred metres) coastal ice caps or high-­alpine glaciers are much shorter and often extend only over recent decades to a few centuries. Complex flow histories and extreme flow thinning in the basal ice layers of thin high-­alpine glaciers make reliable dating through modelling challenging and annual layer counting all but impossible regardless of the measurement resolution. Recent improvements in carbon-­14 dating offer the potential to constrain dating of basal sections of high-­ alpine cores, although the low organic carbon concentrations together with the small volumes of available ice mean that uncertainties are still quite large (typically hundreds of years) (Jenk et al. 2006; Sigl et al. 2009; Preunkert et al. 2019; Fang et al. 2021).

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­Ice Core Record  Non-native

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Ag e[ ye ar Gr CE Dween ] a a Wi rf b lde Ju llow irch r-typ nip t yp e Tre er e eb irc h-t Pin yp e e Sp Fir ruce Ha Gr zeln ey ut Elm a Be ldertyp ec e Tre h es a Gr nd e Gr en shr He eenlland ubs rbs an tre d s es hr u bs Gr as s e Ar tem s Go isia o Da sef i o Se sy fa ot Kn dges mily o Ne t w C Ribttle eed Do worfami ck t p ly f la Mi amil ntai cro y n-t yp SC char e co P al

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Figure 9.11  Microfossil-­based environmental reconstructions from polar and high-­alpine ice archives. (a) Microfossil record of Summit Eurocore’89 in Central Greenland shows pollen-­based vegetation reconstruction with the indication of taxa growing in Greenland including introduced taxa by the Old Norse (adventive taxa) and taxa not growing in Greenland. AP = arboreal pollen (trees and shrubs), NAP = non-­arboreal pollen (herbs). Hollow curves = 10 × exaggeration. Source: Adapted from Brugger et al. (2019a). Red bullets highlight major findings in the microfossil record. (b) Microfossil record of Tsambagarav ice core in the Mongolian Altai shows vegetation (summary curves for pollen) and fire reconstruction (microscopic charcoal concentrations) together with selected nomadic empires in Central Asia (Rogers 2012). Green numbers indicate climatically induced forest minima phases followed by fire activity maxima. Source: Adapted from Brugger et al. (2018b).

Some Future Directions Recent analytical advances, coupled with improved sample handling techniques, have revolutionized ice core science, making it a rapidly evolving discipline that has produced exciting new findings related to ancient history and archaeology (e.g. Figures  9.8, 9.9, and  9.11). These and ongoing measurement innovations lead to a number of possible future directions especially relevant to multi-­ disciplinary studies involving environmental and social sciences, as well as the humanities. Improved Ice Core Chronologies

Multi-­disciplinary studies frequently involve linking ­disparate types and sources of information such as paleoenvironmental records and historical documents. Accurate, independent chronologies for these different types and sources of information underpin robust linkages and so more quantitative interpretation and understanding; such as the vulnerability of past societies to volcanic and other climate shocks (Sigl et  al.  2015; Manning et  al.  2017),

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plagues (McConnell et al. 2018, 2019), or other externalities. Recent advances in ice core analyses mean that far more high-­time-­resolution, broad spectrum records suitable for robust annual layer counting (Sigl et  al.  2015; McConnell et al. 2018) and CH4 synchronization (Rhodes et al. 2015) recently have become available. Together with development of new chronological age markers, these advances have allowed exact synchronization of different palaeoenvironmental records, not only leading to improved understanding of the Earth System such as close linkages between volcanic eruptions and short-­term climate variability but also to relationships between the environment and ancient societies. For example, the discovery of pronounced, short-­lived increases in cosmogenic nuclides in tree-­core and ice core records provided crucial, unambiguous chronological tie points that underpinned robust synchronization between these two paleoenvironmental archives during the past 2500 years – ultimately resulting in more accurate ice core chronologies, comparable improvements in the history of explosive volcanism, and clear, quantitative demonstration

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that explosive volcanism is the primary driver of short-­ term temperature variations (Sigl et al. 2015). It is highly likely that additional short-­lived cosmogenic nuclide events will be discovered that will improve ice core to ice core record and ice core to tree-­ring record synchronization and extend such synchronizations back in time (e.g. O’Hare et al. 2019). The accuracy of chronologies in ice core and other palaeoenvironmental records such as from marine sediment cores will continue to improve as recently developed methods are applied to additional archives and as new methods for dating and synchronization are developed. Provenance and Atmospheric Processes Using Isotopes

Ongoing improvements in the analysis of isotopic ratios in water (ice) (Schoenemann et  al.  2014; Steig et  al.  2014), aerosol-­related impurities (Rosman et al. 1997; Vallelonga et al. 2002), and gases (Ferretti et al. 2005) are resulting in exciting new discoveries. For example, isotopes of carbon and hydrogen in ice core records of CH4 have been used to separate natural (e.g. wetlands, wildfires, termites, ocean sediments) from anthropogenic (e.g. rice paddies, ruminants, landfills, natural gas extraction, biomass burning) sources, and suggest that human activities altered global atmospheric CH4 well before the period of western industrialization (Ferretti et  al.  2005; Mischler et  al.  2009). Similarly, lead isotopes measured in Greenland ice were used to identify pollution from Greek and Roman-­era mining and smelting (Rosman et al. 1997). In addition, while ice core records have been widely used for volcano and palaeoclimate research for decades (e.g. Zielinski et  al.  1994), sulfur isotopes in volcanic fallout found in ice recently have been used to better quantify the magnitude of past eruptions and atmospheric transport pathways for the sulfur, leading to a better understanding of potential source eruptions and climate effects. Sulfur dioxide emitted by eruptions is converted in the atmosphere to bright, highly reflective sulfate aerosols that reflect incoming solar radiation and so result in cooling at the Earth’s surface. In general, the larger the eruption, the greater the cooling although the location (i.e. latitude), seasonality, and height of injection into the atmosphere also play a role. The duration of the climate impact is largely determined by the atmospheric lifetime of the sulfate aerosol. Because sulfate is highly soluble, it is readily scavenged by precipitation, so the lifetime in the lower atmosphere (i.e. troposphere) is short. For especially large eruptions where the eruptive plume penetrates into the much dryer and stable upper atmosphere (i.e. stratosphere), the atmospheric lifetime of the sulfate aerosol is much longer, so the climate effects are both longer lasting and more widespread. Because of mass-­independent fractionation in the

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high ultra-­violet environment above the ozone layer in the lower stratosphere, sulfur isotope ratios in volcanic fallout provide a means to determine if an eruption penetrated above the lower stratosphere (Baroni et al. 2007). With measurement technology improvements, for example in sulfur isotopes (Paris et al. 2013), analytical costs and the amount of ice core meltwater or gas required for precise isotope measurements will continue to decline, so many more detailed isotope records will be developed from ice cores, leading to better understanding of the provenance of impurities and gases in ice, and so improved interpretation of palaeoenvironmental records from ice cores. Volcanic Reconstructions Using Microtephra Analyses

Climate and societal effects of a volcanic eruption depend on its location, seasonal timing, and magnitude. Tephra geochemical fingerprinting is used for source identification in cases where volcanic tephra or ash particles were preserved in the ice as part of the volcanic fallout (see Chapter 8). Traditional studies of tephra in ice, peat, and lake and marine sediment (Óladóttir et al. 2020), as well as other paleoenvironmental records were made on tephra particles larger than ~30 μm and in early ice core studies, only volcanic tephra from visible layers was analyzed. More recently, continuous, size-­resolved measurements of insoluble particles, coupled with continuous, non-­sea-­salt sulfur or acidity measurements, have been used to identify invisible diffuse tephra layers (Figure 9.8). In addition, new methods recently have been developed to geochemically fingerprint much smaller (5–10 μm) tephra particles filtered from the ice (e.g. Davies  2015; Dunbar et  al.  2017; McConnell et al. 2017). As more cores are analyzed in the future using continuous flow analysis systems, more diffuse tephra-­bearing volcanic fallout events will be identified in ice and the provenance determined using geochemical fingerprinting of cryptotephra, particularly as volcanologists expand their databases of volcanic eruptions with known geochemical fingerprints based on collection and analysis of proximal reference tephras (Davies 2015). The result will be a much better understanding to the effects of explosive volcanism on climate and ancient societies. Improved Climate and Other Modelling

Ice core and other palaeoenvironmental records underpin Earth System, aerosol transport and deposition, and other climate models, but these sophisticated models also allow more quantitative interpretation of ice core and other ­paleoclimate records, as well as linkages to ancient history (e.g. Figure 9.9). For example, ice core records of the seasonal timing (based on annual layer counting), magnitude

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­Ice Core Record 

(from fallout patterns measured in arrays of ice cores), the height of injection (from sulfur isotopes), and sometimes location (if tephra geochemistry can be used to identify provenance) underpin detailed Earth System model simulations. When evaluated against climate proxies such as tree-­ring or speleothem records, these improved simulations allow more quantitative understanding of how climate shocks from specific eruptions may have affected ancient societies (Sigl et al. 2015; McConnell et al. 2020). Chemical interactions also occur in the atmosphere during transport and deposition, and these processes may affect the palaeoenvironmental records archived in ice (Legrand et  al.  2018). For example, acidity controls many chemical reactions in air and precipitation, so palaeoenvironmental records of seemingly unrelated chemical compounds may be substantially altered during periods of high acidity (e.g. after volcanic eruptions or resulting from anthropogenic activities such as recent fossil fuel burning). Further improvements in aerosol transport and deposition (e.g. FLEXPART: Stohl et al. (2005), Eckhardt et al. (2017)), atmospheric chemistry (e.g. GEOS-­CHEM: Legrand et  al. (2018)), Earth System (e.g. CESM: McConnell et  al. (2020)), and other models, complemented by additional development of high-­time-­ resolution, accurately dated ice core records, will enable additional, more quantitative linkages between paleoenvironmental records and ancient societies.

reflected the introduction of non-­native species to sensitive Arctic vegetation communities by Medieval settlers, and the record showed that birch woodland expansions after 1850 ce (Betula alba-­type in Figure 9.11) were interrupted as early as ~1900 ce probably as the result of human activities such as sheep herding and wood collection in the sub-­Arctic. The first signs of coal burning-­related spheroidal carbonaceous particles (SCP) in the ice core at the end of the nineteenth century coincided with the documented onset of Arctic coal mining, and coal and fire activity increased steadily during the twentieth century. Similar measurement techniques allowed development of a microscopic charcoal-­derived fire record, combined with pollen-­based vegetation data, from the high-­alpine (4130 m asl) Tsambagarav glacier core, the first long record in the central Asian region. The records led to better understanding of palaeoenvironmental conditions during the late-­Holocene in the Mongolian Altai region (Brugger et al. 2018b), and several late-­Holocene boreal forest expansions, contractions, and subsequent recoveries related to moisture regime changes in the area affecting both forest ecosystems and fire regimes were identified. Further development and application of these techniques to archived and new ice cores from polar and high-­alpine regions will lead to better understanding of linkages between climate, human activities, and environmental change.

Terrestrial Microfossil Records From Ice

New Archives in Permanent and Semi-­Permanent Ice Patches

Terrestrial microfossils (e.g. pollen, spores, charcoal) in ice archives reflect past environmental dynamics such as past vegetation, land use, or fire activity on regional to subcontinental spatial scales. With higher temporal resolution and more precise dating than traditional lake sediments, these ice archives offer the potential to study relatively short-­term activities such as human settlement phases. However, glaciers generally contain extremely low microfossil concentrations compared to lake and peat sediments, so only a few records have been developed from polar ice archives (e.g. Brugger et  al.  2019a), high-­alpine glaciers (e.g. Liu et  al.  1998; Reese et  al.  2013; Brugger et  al.  2018b,  2019b), and ice caves (Leunda et  al.  2019). Pollen extraction methods from ice are based on evaporation, filtration, or centrifugation before standard chemical sample processing (Brugger et al. 2018a, 2019c). New methods for microfossil measurements even at extremely low concentrations recently have been developed and applied to samples from the central Greenland Summit Eurocore’89 core. The record provided new insights into the broad-­scale impacts of industrialization and climate change on remote Arctic environments during the past 300 years (Brugger et al. 2019a). For example, pollen from adventive plant species (e.g. Ranunculus, Rumex)

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The discovery of archaeological artefacts emerging from melting high-­alpine glaciers, perhaps the most famous example being the 5300-­year-­old Ötzi ice man discovered in northern Italy (Spindler 1994), has led to an emerging field referred to as ‘glacial archaeology’. While many of the discoveries in this field worldwide have been associated with alpine glaciers, in both North America and Europe, many artefacts have been discovered melting out of much smaller, semi-­permanent ice patches. Unlike glaciers, these small ice patches do not have clearly defined accumulation and ablation zones and are too small to flow under their own mass. Since artefacts emerging from these ice patches were encased in ice until their discovery, archaeologists have found remarkably preserved artefacts, including a 1700-­year-­old tunic in Norway (Vedeler and Jorgensen 2013) and a 10 000-­year-­old wooden hunting foreshaft in the Rocky Mountains (Lee 2012). The age of the artefacts emerging from these ice patches – in some cases over 10 000 years old  – indicates that ice patches contain ice substantially older than basal ice found in much larger mountain glaciers, likely a result of their non-­flowing interior. Whereas constant interior flow and basal melt in an Alpine glacier results in thinning,

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distortion, or loss of the bottommost oldest ice, the stable interior of an ice patch preserves the stratigraphy of the deepest, oldest ice. These alpine ice patches have the potential to be an ice archive that directly links archaeology, via the artefacts preserved within the ice patch, to local and regional climate, using the chemistry of the ice (Chellman et  al.  2020). However, more work is needed to better understand how and why ice patches form and persist, and also, if similar to polar and glacial ice, ice patch chemistry reflects past climate and atmospheric conditions (Reckin 2013).

tsunamis and earthquakes, and terrestrial environmental change (Taylor and Aitken 1997; Daniau et al. 2013). Marine sediment cores encompass iconic long-­term records (Figures 9.1 and 9.12) that span much or all of the Quaternary (e.g. Hays et al. 1976; de Vernal and Hillaire-­ Marcel  2008), to short-­term records of a few months to decades representing the historical period (e.g. Chabaud et  al.  2014; Poliakova et  al.  2014; Incarbona et  al.  2019). Marine sediment cores are distributed geographically around the globe, for example in the Arctic Sea, the Pacific, or the Mediterranean (Figure  9.2), and locations range from near-­shore to off-­shore deep sediment cores (e.g. Chabaud et al. 2014). Recent studies directly link marine sediment core data with archaeology, for example by associating multi-­century warm winter and wetter climates with the expansion of Central and Northern European Neolithic populations (Goni et  al.  2016), thereby providing important environmental and climatic context to human activities. In addition, marine sediment processes, especially in the

­Marine Sediment Records

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Marine sediments record a number of important climatic and environmental changes that have influenced human activities in the past. For example, they reveal past sea-­level changes that established bridges between land masses, changing sea surface temperatures (SST), drought periods,

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Figure 9.12  Environmental reconstructions from marine sediment cores. (a) Northern European vegetation reconstruction during the Linearbandkeramik (LBK) period from a site in Trondheimsfjord (central Norway) showing selected tree taxa as percentages of the pollen sum. Source: Adapted from Goni et al. (2016). (b) Biomass burning variability of southern Africa over the last 170 000 years from a marine sediment core offshore in Namibia showing benthic foraminifera δ18O, the terrigenous fraction (Al + K + Ti + Fe) obtained from XRF scanning, and microscopic charcoal concentrations to infer fire activity. Source: Adapted from Daniau et al. (2013).

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­Marine Sediment Record 

uppermost sediment layers, are important for local and global biogeochemical cycles of many elements, such as the reduction of nitrate to gaseous N2 (denitrification), an important component of the global nitrogen cycle that plays a key role for regulating reactive nitrogen on glacial-­ interglacial timescales (Ren et al. 2017).

Components and Formation of the Marine Sediment Archive The composition of marine sediments is controlled by initial deposition of material to the seafloor but then modified by chemical, biological, and physical processes that affect the sediment after deposition. Sediment material can be divided into inorganic and organic components, and the inorganic component further divided into three types based on the origin of the material and deposition ­processes  – detrital or terrigenous, biogenic, and authigenic (Burdige 2006). Inorganic Material

Detrital or terrigenous material originates from physical and chemical land erosion of particles that are transported by rivers or wind to the ocean floor or in a smaller amount derive from volcanic eruptions and cosmogenic origin. These physical transport processes of active and passive sedimentation dominate at the ocean margins (Burdige 2006). Biogenic components, such as calcium carbonate or ­opaline silica, are produced by living organisms (e.g. foraminifera) in the water column of the ocean through biomineralization (Pearson  2012). Such biological processes are important for sediment formation in biologically highly-­productive areas that receive little terrigenous material. Examples of such areas are the Equatorial Pacific or the Southern Ocean (Burdige  2006). Additionally, bioturbation by benthic organisms actively mix the most recently deposited sediments and modify sediments, hindering the temporal resolution and interpretation of such records (Aller and Cochran 2019). Authigenic material forms in situ through precipitation from seawater, in the sediment, or at the sediment-­water interface through chemical reactions with existing sediment material. Such chemical processes dominate sedimentation in deep-­sea areas that largely are shielded from terrigenous material inputs and are in low-­ productivity zones (Burdige 2006). Organic Material

Most of the organic matter is either of marine origin, such as phytoplankton debris, or of terrestrial origins, such as soil organic matter, terrestrial biomass, and black carbon from incomplete biomass burning. Additionally, a fraction

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of the sediment particulate organic matter that was remineralized earlier on may be reassimilated as new bacterial biomass. This bacterially derived production of organic matter in sediments is not a new source of organic matter but plays a role in the preservation of sediment carbon. For a comprehensive review of the geochemistry and classification of marine sediments, see Burdige (2006).

Sampling the Marine Sediment Archive Marine sediment coring has a long tradition, with the first coring campaigns dating back to the HMS Challenger expedition of 1874–1876 (Lynch-­Stieglitz and Keigwin 2015). Based on marine sediment cores from the German Meteor Expedition of 1925–1927, Schott (1954) proposed that changes in Pleistocene climate are reflected in warm vs. cold planktonic foraminiferal fauna. The invention of the Kullenberg piston corer and its application by the Swedish Deep-­Sea Expedition of 1947–1948  marked the birth of modern paleoceanography. Today, marine sediment coring systems can be classified by their penetration depth, complexity, and shipboard requirements. See Loring and Rantala (1992) for details on collecting sediment ­samples and Lynch-­Stieglitz and Keigwin (2015) for a comprehensive overview on coring systems.

Analyzing Marine Sediment Cores The age of marine sediments and associated chronologies are determined by a variety of dating techniques often combined to determine the age of a sequence (Deino et al. 2019). Depending on the age of the material, different dating methods can be applied with uncertainty generally increasing with sediment age. Lithostratigraphy is based on the boundaries between different rock or sediment layers, which can be established by seismic reflection profiles (seismic stratigraphy). Changes in foraminifera communities reflect not only past SST but the evolution of species over time (Pearson 2012). The presence or absence of fossil indicator species underpin biostratigraphic dating. For example, back to the Cretaceous, planktonic foraminifera are important indicator species for geological time periods because of their global distribution in marine environments (Pearson  2012). In addition, radiometric methods using lead-­210 (210Pb), 14C, and uranium-­thorium (U─Th), tephrochronology, or the optically stimulated luminescence (OSL) technique are used to determine the age of sediment layers, although changes in the carbon-­14 in the ocean (i.e. marine reservoir effect) can complicate interpretation. For older marine sediments, reversals of Earth’s magnetic field can be recorded in sediments and used to determine their age (magnetostratigraphy). Oxygen

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isotopic compositions of carbonate material (e.g. foraminifera), are a signal driven by global ice storage on the continents during glacial times and can be used to infer past climate but also to build stable isotope stratigraphies as well as to directly link marine sediments between each other and to ice cores (Wright 2000; Waelbroeck et al. 2019). In summary, the most important methods to establish ­chronologies of marine sediments are biostratigraphy (Mesozoic and Cenozoic sediments), magnetostratigraphy (late Cenozoic sediments), and oxygen isotope stratigraphy  (Pleistocene sediments). For a comprehensive overview on  marine sediment dating methods, see Turekian and Bacon (2014). Accurate sampling of sediments and sample processing are crucial to obtain robust results and well-­established sampling methods for marine sediments, from initial subsampling, drying, determination of water content, and removal of sea salt to sedimentological analyses (grain size) and geochemical analyses such as chemical partitioning of sediments are used (Loring and Rantala  1992). Additionally, recent advancements of nondestructive methods such as XRF scanning allow measurements of >60 elements or ratios and document a wide range of environmental and sediment process changes without contacting the sediment core (Rothwell and Croudace 2015).

Limitations and Caveats of Marine Sediment Records Similar to ice core records, the interpretation of marine sediment cores can be complicated by potential archive limitations such as stratigraphic features, chronological uncertainties, and methodological limitations for analysis, some of which will be addressed here. Changing Sediment Accumulation Rates and Incomplete Stratigraphic Sequences

The thickness of marine sediments from the seafloor to the underlying bedrock varies depending on location. For example, average sediment thicknesses are more than 1 km in the Atlantic Ocean but less than 1 km in the Pacific Ocean (Burdige  2006). Sedimentation rates for deep-­sea sediments are lower (~50–100 mm per 1000 years) and increase towards shorelines to as much as several tens of mm per year (Burdige 2006), thus affecting the time span and resolution of retrieved sediment cores. Although sediment accumulation rates in coastal areas are commonly higher, some of these sites can have a sediment supply deficiency or be affected by erosion (Turekian and Bacon 2014). Between the deep sea and onshore, most of the sediments on the continental shelf were deposited during low sea level stands in the last ice age and currently are not

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accumulating new sediment (Burdige 2006). Additionally, at deep sea sites, bottom sea currents can redistribute arriving particles from areas that are topographically higher to lower zones (Turekian and Bacon 2014), thereby increasing the sedimentation rate above that from the settling pelagic sediments alone. The process of exceeding sediment accumulation rates compared to local pelagic rain is called ‘sediment focusing’, a transport process that tends to smooth horizontal sharp sediment changes across an area (Lyle et al. 2005). Marine sediment records, and thus their interpretation, may be affected by changing sediment accumulation over time or alternating sets of depositional events with sediment increments and hiatuses, the ratio of which is referred to as ‘stratigraphic completeness’ (Sommerfield  2006). Hiatuses are periods either without deposition of sediment material or erosional processes that remove previously deposited sediment material. Accounting for missing time periods in a sediment stratigraphy is crucial for interpreting the derived record, but especially small hiatuses are often indistinct in the lithology making it challenging to achieve accurate chronologies (Sommerfield 2006). Chronologies and Temporal Resolution

Precise chronologies are important to interpret the marine sediment record (e.g. Waelbroeck et  al.  2019). Dating uncertainties have implications when synchronizing marine sediment records and their signals over larger spatial scales since temporal uncertainties of specific features in the individual records may not unambiguously be assigned to a common event. Contrary to ice archives, marine sediments provide no yearly signal to establish absolute chronologies apart the few sites with yearly sediment laminations (varves) that have uncertainties of just a few years (Schimmelmann et al. 2016). Accurate dating of marine sediment records additionally is complicated by factors such as dating methods, strategy to collect samples for dating, and inherent factors in the sediment column such as hiatuses or rapid sedimentation rate changes. Generally, dating uncertainty increases with sediment age, similar to ice core archives. Additionally, radiocarbon dating of marine sediment records is complicated by the so-­called marine reservoir effect – a difference in the radiocarbon ages between contemporaneous organisms that consume atmospheric carbon vs. organisms consuming carbon from the marine environment (see Chapter  2)  – resulting in an offset of derived radiocarbon ages that has to be accounted for (Ascough et  al.  2005). The site-­specific reservoir age of the surface water depends on the equilibrium between atmospheric C-­14 input and its elimination by a combination of radioactive decay in the water column, mixing with older waters

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and advection (Waelbroeck et al. 2019). Previous studies in the North Atlantic Ocean suggest, however, that the reservoir ages of the surface water may not have remained constant over time at high latitudes (Waelbroeck et al. 2019). Recent studies have improved marine sediment chronologies and reduced the problem of surface reservoir age uncertainties by matching chronostratigraphic tie-­points of the SST signal in marine sediment records and temperature records in polar ice cores and speleothems (Skinner et  al.  2010; Waelbroeck et  al.  2019). Turekian and Bacon (2014) address limitations of the different dating methods for the respective marine sediment types in more detail.

Some Future Directions Molecular Biomarkers

Fossils from marine sediment cores such as foraminifera, dinoflagellate, pollen, or charcoal are established proxies to reconstruct marine or terrestrial ecosystems over time on near-­shore sediment cores and provide important information on the environment of early hominin populations (de Vernal and Hillaire-­Marcel 2008; Daniau et al. 2013; Eynaud et al. 2016). Sánchez Goñi et al. (2016) give a comprehensive overview on pollen records from marine sediments. Recent analyses of molecular biomarkers allow the integration of the marine and terrestrial biosphere on many timescales and permit detailed reconstructions of past vegetation and hydrological change (Lynch-­Stieglitz and Keigwin 2015). Multiproxy studies based on several lines of evidence have the potential to constrain leads and lags of environmental change and to gain a better understanding of processes driving individual proxies (Sikes et  al.  2019). New emerging molecular biomarkers such as environmental DNA and glycerol dialkyl glycerol tetraether lipids (gdgts) may provide new directions for the field and add novel information on past climate and environmental change (Schouten et al. 2013; Armbrecht et al. 2019). Non-­Destructive Methods

Measurement with physical and chemical methods is both time-­consuming and expensive, which limits sample numbers and resolution (Rothwell and Croudace  2015). Therefore, rapid non-­destructive scanning and imaging approaches are becoming more important. New developments as well as improvement of existing non-­destructive core scanning systems open new fields for rapid and high-­resolution sediment core analyses. For example, the recent advancement of micro-­X-­ray fluorescence (μXRF) (Rothwell and Croudace 2015) and hyperspectral imaging currently applied in lake sediments to estimate, for example algae productivity (Butz et  al.  2015) or computer tomography methods to scan for fossils or facies

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determination are emerging fields for marine sediment analyses (Dorador et al. 2020). Varved Sediments and Records of Multidecadal Variability

Climate phenomena such as the Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, or El Niño-­Southern Oscillation (ENSO) are still poorly understood, and foraminifera, as well as coral records that capture multidecadal variability, will be crucial to gain a better understanding beyond the measurement record (Lynch-­Stieglitz and Keigwin  2015). Developing records from varved marine sediment sequences may help to address such questions and provide a tool to reconstruct climate and environments on extremely high temporal resolution (Schimmelmann et al. 2016) appropriate to directly compare with short-­term societal dynamics from archaeological data or historical documents. Such records may geographically complement and extend information from varved lake sediment records (e.g. Rey et  al.  2019) and ice cores (e.g. McConnell et al. 2018) recently developed to address such questions.

­ onclusions and Implications C for Archaeology The evolution of human societies is inextricably linked to the environment. Records extracted from natural archives such as glacier ice and marine sediments provide detailed, quantitative information on the environment extending hundreds to thousands to millions of years in the past, potentially leading to new interpretation and understanding of historical and archaeological events. Human societies were and are influenced by environmental ­factors  – for example, the extreme, often hemispheric to global-­scale cooling associated with large volcanic eruptions that sometimes disrupted food production and contributed to famines, wars, and political realignments (McConnell et  al.  2020). However, human activities also influenced the environment at local to hemispheric scales, so records extracted from natural archives also potentially provide objective, quantitative information about past human activities not available from traditional historical and archaeological sources  – for example, year-­to-­year changes in silver production during antiquity through precise, well-­dated measurements of lead pollution archived in Greenland ice (Hong et al. 1994; McConnell et al. 2018). Recent advances in analytical methods and modelling, together with the development of new, more spatially representative records and improved chronologies, suggest the expanded use of environmental records from natural archives in future historical and archaeological research.

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10 Insects as Palaeoenvironmental and Archaeological Indicators Stefan Engels1 and Nicki J. Whitehouse2 1 2

Department of Geography, Birkbeck University of London, London, UK Archaeology, School of Humanities, University of Glasgow, Glasgow, UK

Insects are an incredibly diverse class of animals, with probably over one million species described and estimates of total species richness ranging between 3 and 80 million (Gullan and Cranston  2014). As such, insects make up about half of the total number of species known to science (Gullan and Cranston 2014). Insects are not only diverse, they are also very abundant, occurring in high numbers in nearly all terrestrial and freshwater habitats in the world. For example, the non-­biting midge Belgica antarctica Jacobs can be found living on the ice-­sheet of Antarctica where it is the largest terrestrial animal native to the continent. Another extreme example is the sleeping chironomid Polypedilum vanderplanki Hinton, which lives in temporary pools in Africa. It tolerates desiccation by lowering its body’s water content to values as low as 3% and can survive being exposed to temperatures from –270 to +102 °C (Hinton 1960). Many insect species are stenotopic, adapted to particular habitats and conditions, which makes them excellent indicators for reconstructing past environments and conditions. Good examples include the heather beetle Micrelus ericae Gyll., which is stenotypic on Calluna and Erica (Hyman  1992), whilst the rove beetle Pycnoglypta lurida Gyll indicates cool climatic conditions, tolerating winter conditions of between –0.4 and –24.5 °C (http:// www.gbif.org, Milne 2016). Insects have a chitinous exoskeleton, a body that can be divided into three main parts (head, thorax, and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. Whilst many insects hatch from eggs, their individual life cycles differ from species to species. There are two main forms of insect development. The first is holometabolism or complete metamorphosis, where an individual goes through four life stages: egg, larva, pupa, and imago (adult). Alternatively, insects can go through hemimetabolism or

incomplete metamorphosis, which only knows three life stages: egg, nymph and imago, where the nymph resembles the adult stage. Some species pass from one stage to the next relatively rapidly, whilst others can remain in, for example, their larval stage for considerably longer than their adult stage. For example, the longhorn beetle Cerambyx cerdo L., a saproxylic species that lives on sun-­ exposed trees, takes between two and five years to develop (Torres-­Vila  2017), whilst the water beetle Hydraena riparia L. goes through its entire lifecycle within a ­single season. Insects may live in a variety of habitats including on land, vegetation, decaying matter, in soils or in freshwater habitats. For many species, the habitat of the larva (e.g. on the sediment-­water interface of a lake) is very different from that of the adult (e.g. free-­flying). Similarly, feeding strategies can differ dramatically between different life stages. In general, insects feed on a wide variety of living, dead or decomposing organic material and are essential for a number of ecosystem functions, including nutrient recycling, decomposition, plant propagation including pollination, maintenance of plant community composition, and maintenance of food webs and animal community structures, either as predators, as prey, or through the transmission of diseases or parasitism (Gullan and Cranston 2014).

I­ nsects in Palaeoenvironmental and Archaeological Studies Factors such as the habitat of species, the level of sclerotization of their exoskeleton (i.e. how hard or thick is it), their abundance, and the duration of their lifecycle all ­contribute to the likelihood of the insect leaving behind

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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remains for study by archaeologists or palaeoecologists (Figure 10.1). Whilst there are over a million of described species of insects in the world, in reality, there are only a number of insect orders or families that are regularly used as palaeoenvironmental indicators, with Coleoptera (beetles) and Chironomidae (non-­biting midges) probably being the most commonly studied taxa. The order Coleoptera is the most species-­rich order of insects, and beetle remains often are the most abundant insect fossils identifiable from terrestrial and water-­lain organic sediments such as peat, clays and silts, and organic-­ rich archaeological sediments. Beetle fossils are frequently identified to a high level of taxonomic resolution (often species level), and beetles have highly specific ecological niches that are well known in the ecological literature. Their specific preferences around winter and summer temperature requirements, moisture levels and aquatic conditions, landscape characteristics (open/closed), or host trees and plants allow them to be used as excellent quantitative and qualitative indicators in palaeoecological studies. Many beetle species feed on or live on specific plants, whereas others are carnivorous. Aquatic species provide detailed information on water quality, nature and quality of the aquatic and wetland habitat (Whitehouse et al. 2008), whilst other species are characteristic of old deciduous or coniferous woodland (e.g. Olsson and Lemdahl  2010).

Fossil beetle assemblages have been used to reconstruct the structure of local to regional landscapes (Buckland  1979; Whitehouse and Smith  2010) and have provided insights into past beetle diversity change, extirpation, extinction, and endemism (Whitehouse 2006; Liebherr and Porch 2015). Some species are synanthropic, e.g. occurring as pests (e.g.  King et  al.  2014) and are strongly associated with human-­made habitats (Smith et al. 2020), whilst others are associated with the dung of grazing animals and open ­habitats (Skidmore  1991; Robinson  2001): these groups are useful for interpreting past human activity or lifestyle. The distribution range of a modern species is used to ­determine the climatic envelope in which a species can occur. This information can subsequently be used to quantitatively reconstruct climate parameters such as past summer temperatures, winter temperatures or seasonality from fossil beetle assemblages (e.g. Atkinson et al. 1987; Coope et al. 1998; Langford et al. 2017). Chironomids (Insecta: Diptera: Chironomidae) or non-­ biting midges are an insect family whose larvae are predominantly aquatic and are encountered in most freshwater environments on the planet. Parts of the larval exoskeleton preserve well in lake sediments and whilst they cannot typically be identified to species level, they are used as qualitative or quantitative indicators of past changes in summer temperature (Heiri et  al.  2014), lake level

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Figure 10.1  Images of subfossil insect remains as assemblages during sample preparation (a) beetles, (e) chironomids, of individual beetle remains (b) Rhyncolus sculpturatus Waltl.; (c) Temnochila caerulea Olivier; (d) Bothrideres contractus Dejean and individual chironomid head capsules; (f) Chironomus anthracinus-­type; (g) Microtendipes pedellus-­type; (h) Dicrotendipes nervosus-­type. Source: (a–d) by N. Whitehouse; picture; (e) Courtesy of C. Francis, Royal Holloway University of London, UK; (f–h) Courtesy of J. van Arkel, IBED, University of Amsterdam, NL.

­Insects in Palaeoenvironmental and Archaeological Studie  189

(Engels and Cwynar 2011), salinity (Dickson et al. 2014), hypolimnetic oxygen (Quinlan and Smol  2001), trophic levels (Nyman and Korhola 2005) as well as other environmental variables. Recent studies have furthermore focused on the reconstruction of chironomid diversity change on timescales ranging from multiple glacial/interglacial cycles to the ‘Anthropocene’ (Engels et al. 2020).

Aside from Coleoptera and chironomids, there is a much wider range of insect orders and families that are regularly encountered in palaeoecological and archaeological contexts and that can be used as indicators of past environmental and living conditions. Table  10.1 provides an overview of some of the taxa most commonly encountered and provides information on their habitat requirements

Table 10.1  Insect orders and families used in palaeoenvironmental studies. Common name

Linnaean classification

Bees, wasps, and ants

General information

Palaeoenvironmental potential

Order: Hymenoptera

Large order of insects, occurring in large range of habitats.

Subfossil head capsules can preserve well in peat or lake sediments but are hard to identify beyond family level. Ant remains frequently occur in peats (raised, fen) and archaeological samples. Robinson (1993) highlighted they would merit specialist attention, but little work has been done on them.

Beetles

Order: Coleoptera

Live in all types of habitats on land and freshwater. Subfossil remains typically identified to species or genus level.

Used to reconstruct a variety of freshwater and terrestrial palaeoenvironments.

Biting midges

Order: Diptera Family: Ceratopogonidae

Larvae are aquatic; encountered in still water (between plants) and in running water. Subfossil remains are typically not identified beyond family-­level.

Subfossil head capsules similar to those of chironomids. E.g. used as qualitative indicators of past riverine inflow into lakes (Brooks et al. 2007).

Black flies

Order: Diptera Family: Simuliidae

Larvae are aquatic living in running water. Subfossil remains are typically not identified beyond family-­level.

Head capsules encountered in lake sediments can be used as indicators of past (riverine) inflow (Currie and Walker 1992).

Butterflies and moths

Order: Lepidoptera

Second-­largest order of insects. Wings of adults are scaled, and individual scales fossilise in organic sediments.

Some wing scales can be identified to species level, others to morphotype. Can be used to track occurrence rates of forest pest outbreaks (Milbury et al. 2019).

Caddis flies

Order: Trichoptera

Larvae encountered in a variety of freshwater habitats. Larvae of many species well-­known for building protective cases.

Subfossil remains include mandibles; as many species of Trichoptera are sensitive to nutrient enrichment, used as indicators of changes in trophic status (e.g. Wilkinson 1984, Greenwood et al. 2003).

Domestic flies

Order: Diptera Family: Muscidae

Worldwide in distribution; some species well-­known for their synanthropy. Puparia can be identified to genus or family level.

Often found on archaeological sites with high levels of organic preservation, associated with decomposing plant and animal matter such as dung. Work on domestic flies pioneered through the work of Skidmore (1995) and Panagiotakopulu (2004). Excellent indicators of living conditions.

Dragonflies Damselflies

Order: Odonata

Heterometabolous insects whose nymphs are predatory.

Remains of nymphs and adults sometimes found in aquatic deposits (Robinson 1991, 2001), thought to be of limited palaeoecological value.

Earwigs

Order: Dermaptera

Terrestrial insects mostly feeding on decaying plants and animal material.

Pincers preserve well but are of limited palaeoecological value due to the relatively low species richness of this order (Robinson 2001) (Continued)

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Table 10.1  (Continued) Common name

Linnaean classification

Fleas

General information

Palaeoenvironmental potential

Order: Siphonaptera

Jumping insects feeding on blood of animals and humans.

Sometimes found in archaeological sites that are water-­logged and where there has been close contact with humans or domestic animals (Robinson 2001). Human ectoparasites can be common in historic urban and rural assemblages.

Fungus gnats

Order: Diptera Family: Sciaridae

Small flies often associated with woodlands; larvae feed on decaying organic matter, including roots and stem tissue of plants.

Larval head capsules transported to lakes via streams. Indicators of terrestrial and/or stream input when encountered in lake sediments (Heiri and Lotter 2007)

Lice

Order: Phthiraptera

Parasitic insects, mostly associated with birds but some host-­specific on mammals.

Found in similar conditions as the Siphonaptera (see above).

Mayflies

Order: Ephemeroptera

Common flies whose larvae live in streams and in shallow zones of lakes. Only mandibles preserve well in organic sediments.

Used as indicators of past stream inflow and/or shallow water conditions when encountered in high concentrations.

Mites

Order: Oribatida

Feed on detrital plant and fungal material and are responsible for recycling nutrients. Preserve in abundance in waterlogged peats, organic sediments and archaeological deposits.

Most species are terrestrial or palustrine. Koponen and Nuorteva (1973) and Karppinen and Koponen (1973) demonstrated their value for the study of forest litter, fens, and bogs, and many species are closely tied to plant species or communities. They can be used to understand palaeolimnological conditions including water depth and nutrient status (Erickson 1988). Schelvis (1997) highlights their use in the investigation of archaeological deposits.

Non-­biting midges

Order: Diptera Family: Chironomidae

Larvae living in all types of freshwater habitats. Subfossil head capsules typically identified to morphotype or genus level.

Used to reconstruct a variety of freshwater palaeoenvironments but recently with a strong focus on palaeoclimatological reconstructions.

Phantom midges

Order: Diptera Family: Chaoboridae

Larvae known as glassworms, predators in lake environments where they can be very abundant. Only mandibles preserve in organic sediments, where they can’t be distinguished beyond morphotype level.

As larvae are sensitive to fish predation, increased concentrations of remains can indicate past absence of fish or the existence of lake water stratification.

True bugs

Order: Hemiptera

Species-­rich order of insects, sharing a common arrangement of sucking mouthparts.

Sometimes parts of Hemiptera, such as bed bugs (Cimicidae), are found in association with beetle remains in organic-­rich deposits. It can be indicative of past environment as some true bugs are host-­specific (Robinson 2001).

and their applications in the fields of archaeology and ­palaeoecology. A selection of the most common taxa is discussed in the next sections. As shown in Table 10.1, the diversity of insect remains that can be found in natural archives or in archaeological contexts is very high, as is the variety of applications and the number of studies that present insect-­based inferences of past environmental conditions or human activity. The remainder of this chapter will summarize the most

common applications of insects as palaeoenvironmental and archaeological indicators. We will first describe the approach that is generally taken by discussing the natural archives and archaeological contexts in which subfossil insect remains can be found and detail how their remains can be isolated in the laboratory. We will review the types of information that can be inferred from subfossil insect occurrences and introduce the concepts of qualitative and quantitative palaeoenvironmental reconstructions, before

­The Preservation of Insect Remain  191

providing a number of examples of studies that used insects as palaeoenvironmental and archaeological indicators.

­The Preservation of Insect Remains Many wetlands form sedimentary environments where organic-­rich material accumulates with time, thus forming natural archives. Insect remains can be preserved in these sediments and can be used to provide information on environmental conditions in which human activity took place. Additionally, insect remains can be encountered directly in waterlogged and organic-­rich archaeological contexts, such as floor layers, roofing materials, pits, cess pits, wells, and ditches, and can be used to provide information on past lifestyles, trading patterns, and cultural activities. Occasionally, preservation may also occur through mineralization, mostly in the case of Diptera (fly) pupae and puparia, human ectoparasites, and grain weevils (Carruthers and Smith 2020). Whilst insect bodies consist of various components, typically only the hardest and most weathering-­resistant materials preserve with time. Often these are those parts of the exoskeleton that are composed of chitin, a polysaccharide; amongst beetles these will often be head capsules, thorax and elytra (wing-­cases), whilst in chironomids, this often includes only the head capsules. In suitable settings (e.g. water-­logged conditions such as those existing in lake and wetland environments), chitin can remain unchanged over extended periods of time (Verbruggen et al. 2010; Van Hardenbroek et al. 2018). Preserved parts are often identifiable to species, group, genus or family level, thus enabling the identification of past fauna on timescales ranging from the present back to the onset of the Palaeolithic and beyond.

beetle assemblages, although fen peats tend to be richer in insect remains than ombrotrophic peats (Buckland  1979; Whitehouse 2004; Khorasani et al. 2014), as anaerobic conditions ensure excellent preservation while the rapid build­up of sedimentary deposits provides good temporal resolution. Fen and peat bog records will provide a relatively direct picture of the fauna living locally, as vectors for transport of subfossil remains are more limited in these environments (Whitehouse 2004; Mansell et al. 2014). Fluvial sediments often accumulate material, particularly in secondary channels bends, backflows, and pools, as well as adjacent floodplain deposits (Brown  1997; Smith and Howard  2004), representing both allochthonous assemblages, formed in-­situ, as well as autochthonous assemblages, i.e. composed of material and insect remains from elsewhere. Investigations of modern sub-­surface samples indicate that the catchment of beetle remains is typically derived from a local community (up to 400 m), allowing detailed information about landscape composition through time to be reconstructed on a local scale (Smith et al. 2010). Figure 10.2 shows the variety of different habitats potentially available to insects at the landscape level, which can all contribute to a beetle (or other insect) assemblage collected from a natural archive such as a river deposit or small water body such as a pond. The past two decades have shown a strong increase in the application of the study of subfossil insect remains in sedimentary archives for palaeoenvironmental reconstructions. This has been made possible by the improvements in subfossil taxonomy (e.g. Brooks et  al.  2007), ecological understanding and interpretations (e.g. Buckland and Buckland  2006; Smith et  al.  2010,  2014) as well as the development of increasingly powerful numerical tools for quantitative environmental reconstructions based on subfossil insect assemblages (Birks et al. 2010).

Sedimentary Archives and Taphonomy Lake sediments, fens, and peat bogs are among the most-­ studied natural archives available for palaeoenvironmental reconstructions based on subfossil insects, but palaeochannel fills, floodplain sediments, and sediments formed at the bottoms of human-­made structures like wells provide additional resources for study. For chironomids and lake sediments specifically, the assumption is that the deepest part of the lake receives materials from the littoral as well as the profundal zone due to sediment focusing, a process whereby water turbulence moves sedimented material from shallower to deeper zones of a lake (Blais and Kalff 1995). As such, the deepest part of the lake provides an integrated picture that reflects the diversity and abundance of the living insect fauna of the entire lake. Bogs and fens are very rich sources of fossil

Archaeological contexts The identification of insects from archaeological deposits has been carried out occasionally since the mid-­nineteenth century, but it was only after the publication of Coope and Osborne’s work on the fauna from a Roman well at Barnsley Park (1968) and Osborne’s Roman Alcester study (1971) that their potential for the investigation of immediate archaeological environments was understood. From this, it became clear that insect materials recovered from archaeological materials offered insights of site activities not available from other lines of evidence, especially around living conditions and the use of on-­site organic materials. Considerable urban archaeological work was subsequently pioneered by Kenward at the York Environmental Archaeology Unit (e.g. Kenward  1978,  1997; Hall and

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Woodland, dead wood, nests and tree hollows Grazing

Corpses Aquatic plants

Plant litter

Dung

Figure 10.2  Schematic representation of the different habitats available in a semi-­natural landscape, each supporting their own specialized insect community. Insects from all these habitats can potentially be found in natural archives such as lake and river deposits, as well as archaeological deposits, when transported from off-­site activities (e.g. in fire-­wood, bedding, flooring materials).

Kenward  1980), examining samples from Viking and Medieval houses, cess pits, and wells, all of which typically yield abundant insect fossils. In addition to sampling of urban deposits, there is also a strong history of sampling from rural archaeological sites, ranging from Neolithic and Bronze Age trackways and occupation sites (e.g. Girling 1979; Robinson  1991; Chapman et  al.  2013) to Iron Age settlements (Robinson 1993; Roper and Whitehouse 1997; Crone et al. 2019), bog bodies (Plunkett et al. 2009) and Roman sites, both urban (e.g. Smith 2012) and rural (e.g. Buckland et al. 2019), and Medieval sites (e.g. Hellqvist 1999), especially where waterlogging offered sampling opportunities or where the excavator needed insect analysis to answer site-­specific research questions. Considerable work has been undertaken in the North Atlantic region, where there has been a particularly strong tradition of using insect remains to reconstruct past activities and living conditions on Norse sites in Iceland, Greenland, and the Faroe Islands (Buckland and Panagiotakopulu 2005; Forbes et al. 2014). These latter works were particularly influential in understanding the disappearance of Norse settlements in Greenland and improving the understanding of living ­conditions and resource exploitation on rural Norse farm sites. Insect studies have also been undertaken on Neo-­and

Palaeo-Inuit sites in the North Atlantic region and Canadian artic, providing insights into the daily lives of hunting and gathering groups and their subsistence practices, resource exploitation, and living conditions on hunter-­gatherer settlements (Forbes et al. 2014). The effects of the Little Ice age on these communities have also been investigated, as we elaborate below (Forbes et al. 2019). Outside of the North Atlantic region and Northern Europe, however, the analysis of ento-­archaeological material remains a rarity. The taphonomy of archaeological material is complex and requires a clear and site-­specific understanding of the pathways by which insects become part of the archaeological record (Kenward 1978; Kenward and Allison 1994). It is important to consider the whole assemblage when making archaeological interpretations and to understand the contexts associated with the insect remains and how materials may have become part of the archaeological record  – including the role of humans in transporting organic materials into an archaeological context. Materials such as bedding, roofing, thatching, and flooring are common materials through which insects are introduced into the archaeological record, offering insights into the use and introduction of organic materials on sites (Kenward 1985; Buckland et  al.  1994). Other pathways through which

­Methodolog 

insect remains end up in the archaeological record are more complex; for instance, Smith (2013) discusses the various routes by which insects and plant remains become part of the archaeological record of cess and latrine pits. This is usually through a combination of ingested materials; insects attracted to the foul conditions of the cess pits, and the addition of straw, settlement waste, and other dry materials for the purpose of ‘dampening’ fluid cess materials. Conversely, other insects may occupy a site because they are living within the immediate vicinity, attracted by the volume of on-­site organic materials such as floorings and midden deposits, for example. Figure  10.3 shows a selection of the pathways through which insects can become part of the domestic archeological context. Taphonomic pathways – cultural and natural – thus influence what ends up in the archaeological record. The interpretation of archaeological communities is particularly challenging because of the need to disentangle these differing processes to understand the significance and pathways through which insects become part of the archaeological community. This is done by carefully evaluating the ecological significance of the communities present and considering what may be living in-­situ, what is attracted to the site because of archaeological activities and what is transported to a site by human and animal activities together with performing statistical analyses to understand these various components and their contribution to the whole assemblage.

­Methodology Sampling and Extraction The most suitable method to retrieve sediments for study differs based on the nature of the sediment (e.g. lake sediment, peat), the accessibility (exposure, wetland, archaeological excavation), the age and compaction of the sediment, etc. Typically, if lacustrine sediments, fluvial deposits, or peat are encountered in a sequential order they will be sampled in sampling tubes, cores, or boxes and transported back to the laboratory for cold storage and subsequent subsampling (Last and Smol  2001). When sampling an open sediment sequence for fossil beetle analysis, samples are usually removed in 5–10 cm thick contiguous ‘slices’ usually of at least 3–5 l, taking care not to cross stratigraphic boundaries; if this is not possible, multiple proximal sediment cores in a grid system may be taken that are cross-­correlated (Forbes et al. 2019). In archaeological excavations, large bulk samples of contexts of interest are recommended. The standard recommendation in England is that specialist bulk samples should be in the order of 20 l (English Heritage 2002). Often it may be most appropriate to remove the entire context, such as the fill of a storage or cess pit. For chironomid analysis, subsampling of lake sediment records can be contiguous, and samples typically have a thickness of 1 cm per sample and with a volume ranging between 1 and 10 ml or more (Brooks et al. 2007).

Insects originating within dwelling Insects originating from outside the dwelling

From roof and walls

From stored products

From nests and droppings of predators Insects seeking habitation sites

Parasites of occupants

Accidental entry in local flight In imported material, casual transport, or on occupants Migrating insects Crawling

From litter

Figure 10.3  Selection of pathways through which insects can be incorporated into archaeological contexts.

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Laboratory protocols for sample treatment also differ depending on the nature of the sediment and the type of study. The ultimate goal of many sample treatment procedures is to remove as much of the sediment matrix as possible before hand-­sorting the subfossil insect remains, as this latter step is often time-­consuming. For beetle remains, the extraction procedure follows the approach outlined in Buckland and Coope (1991). Each sample is disaggregated over a 300 μm sieve to remove any clay, silt, and sand fraction from the sample. Paraffin (kerosene) is mixed with the remaining material, and cold water is added. The resulting ‘flot’ is then poured off, washed in detergent, rinsed, and stored in ethanol. For chironomid analysis, a first step of a laboratory procedure might include deflocculating a sample using hot water or KOH (5–10%). If necessary, the sediment sample can be subsequently treated using more destructive techniques including acid treatments (e.g. HF, HCl) or sonic baths in order to remove unwanted clastic and organic compounds. This step can be followed by techniques aimed at concentrating subfossil remains through, for example, flotation, sieving or centrifuging. Hand-­sorting of remains from the remaining material is achieved using a stereo-­microscope under 10–40× magnification and fine forceps, after which individual specimens can be stored in sample boxes and tubes, on cards, on damp filter paper in a petri dish or mounted on microscope slides ready for identification.

Identification, Interpretation, and Presentation Identification of subfossil insect remains is typically achieved using a low-­power dissecting microscope at 40–60× magnification for beetles, ectoparasite and fly remains, and a high-­power microscope under 100–400× magnification for chironomids. The identification of beetle subfossils is carried out through the use of modern entomological keys and through direct comparison with a range of modern comparative materials. Beetles are well described in the literature, and there is an extensive literature of modern entomological keys and online resources that can be used for identifications. Most researchers will require access to a good museum collection; morphological characteristics of the subfossil specimens are described and compared to those of modern material. After identification, the minimum number of individuals (MNI) from the parts recovered are listed and counted. When preserved under anoxic conditions, typically while remaining waterlogged, beetle exoskeletons preserve in such a way that even the microsculpture remains, allowing remains to be identified to species level, enabling very detailed environmental histories and reconstructions to be made. Where many samples are to be examined, however, it may not

always be necessary or desirable to identify all samples to species level, as rapid scanning techniques can often be informative without the time requirement associated with full analysis (Kenward et  al.  1986; Kenward  1992). Ecological information is usually compiled from habitat records and descriptions in the literature, whilst the BUGSCEP database is suitable for analysis of European assemblages https://www.bugscep.com (Buckland and Buckland 2006). The development of the BUGSCEP database, which stores beetle fossil records as well as species’ biological and distributional information, has enabled interpretation to move to a much firmer ecological footing and allowed researchers to tackle a range of broader research questions such as investigating the diversity of aquatic species over long time frames, understanding the long term effects of insect pest attack on forest communities and studying trends in insect biodiversity at a regional level (e.g. Abellán et  al.  2011; Schafstall et  al.  2020a). Species lists are presented in the form of tables of actual counts, often accompanied by transformed summary diagrams representing the main ecological and functional characteristics through a core or site. Identification guides specifically aimed at describing and illustrating subfossil remains have recently become available for chironomids (e.g. Brooks et al. 2007), illustrating the significant progress that has been made in the field of ­subfossil taxonomy for chironomid analysis. For instance, whilst in the 1990s, it was possible to identify nine morphotypes within the chironomid subfamily Tanytarsini, by 2007 a total of 28 morphotypes were identifiable, most of which with their own distinct ecological preferences (Brooks et  al.  2007). Results of chironomid analysis are most commonly presented in downcore diagrams that illustrate changes in concentrations or percentage abundances with time (Figure  10.4). Specialized software is available to produce downcore diagrams, e.g. TILIA (Grimm 2011), C2 (Juggins 2007), or for example the rioja package in R (Juggins 2015; R Core team 2019). Increasingly, datasets of subfossil insect studies are archived in online open-­access databases for use by others, e.g. BUGSCEP (Buckland and Buckland  2006) or Neotoma (Goring et al. 2015).

­Palaeoenvironmental Inferences One of the main goals of analysing subfossil insect assemblages is to reconstruct past environmental conditions, which can be achieved through a number of different approaches (Birks et  al.  2010; Juggins and Birks  2012). First, the occurrence of individual ‘indicator taxa’ can be used to qualitatively or quantitatively infer past

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­Palaeoenvironmental Inference  195

Sediment depth (m)

5.0 5.4 5.8 6.2 6.6 7.0 40

40

40 20 40 Abundance (%)

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20 20 9

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Temperature (°C)

Figure 10.4  Example of a downcore subfossil chironomid record, in this case from palaeolake Sokli in northern Finland. Selected taxa are shown as a percentage of the total chironomid count sum and are plotted against a depth (or alternatively, time) axis. On the far right is a chironomid-­inferred temperature record (in °C) with sample-­specific error estimates. Source: Adapted from Engels et al. (2008, 2014).

environmental conditions or human activity from the ­presence of single species or morphotypes in a palaeoenvironmental record or archaeological context. Second, palaeoenvironmental reconstructions, both qualitatively and quantitatively, can be derived from the entire fossil insect assemblage rather than from the occurrence of a single taxon. Third, the so-­called proxy-­environment calibration approach or transfer-­function approach has increasingly been applied to a range of different palaeoecological proxies. This latter technique has been an especially popular method for chironomid-­based temperature reconstructions and has allowed for the development of high-­resolution quantitative records of past climate change. Below we will further elucidate each of these approaches. All insect-­based palaeoenvironmental inference techniques rely on a number of underlying assumptions, and we refer to Birks et al. (2010) and Juggins (2013) for a more comprehensive discussion on these issues. One of the most important assumptions is that species have undergone ­little or no evolution over the timescales of the study, and that the relationship of a species with its physical environment has remained unchanged. Remarkably, research has highlighted the constancy of exoskeletal as well as genital characteristics over long periods (Angus 1997), and ­evidence for evolutionary change is extremely rare from Quaternary beetle assemblages. Matthews (Matthews 1970, 1979) has been able to show morphological changes in three million-­ year-­old insect faunas, but even here, the changes were

only slight. Some of the earliest beetle identifications came from Kap København, northernmost Greenland, and date to the Plio-­Pleistocene transition (Bøcher  1995), and further demonstrate constancy of ecological niches. Evidence from coleopteran research in Northern latitudes shows a relatively static fossil record, with relatively few absolute extinctions and little evidence of physiological evolution during the Quaternary (Coope 2004). Even though climate fluctuated between extremes of glacial and interglacial conditions, most of the fossil record reflects a degree of evolutionary stasis, with large-­scale range-­shifts as species tracked preferred climate across latitudes (Coope 1995, 2004). Although this general premise holds true for many insect assemblages, the concept of evolutionary stasis merits ­further research attention, as we discuss further below.

Indicator-­Taxon Approach Many insect taxa have strong associations with their environment, and the presence of certain so-­called indicator taxa in a sediment sequence or archaeological context can provide qualitative evidence for past land use or human activities. For instance, the wheat weevil (Sitophilus granarius L.) is almost exclusively found in human contexts, and findings of large concentrations of S. granarius remains in a fossil sample can be used to make inferences about (conditions of) past grain storage (Smith and Kenward 2011, 2013). Additionally, the amount of fragmentation of the heavily

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sclerotized elytra can indicate grinding action and provide further evidence of human activity at the site (e.g. Van den Bos et al. 2014). The indicator approach can also be used to produce quantitative reconstructions of past environmental conditions. This approach relies on an understanding of certain factors that allow or limit an organism to develop and sustain itself, which can be based on modern-­day observations such as distribution patterns of taxa compared to environmental factors (Väliranta et al. 2009), or can be based on controlled experiments, for instance under laboratory conditions (Dickson and Walker 2015). The indicator approach was one of the earliest palaeoecological techniques used to provide quantitative estimates of past temperatures (Iversen 1944) but is limited by the fact it often provides a minimum or maximum expected conditions and doesn’t allow the estimation of uncertainties. It is also sensitive to the absence or presence of indicator taxa and therefore influenced by methodological choices such as count sums or amount of material analyzed. The Mutual Climate Range (MCR) method that is frequently applied to fossil Coleoptera assemblages to reconstruct past climate envelopes (e.g. Elias 1997; Coope et al. 1998) is an example of an indicator approach technique.

Assemblage and ‘Indicator Group’ Based Approaches Whilst important information on past environmental or lifestyle conditions can sometimes be inferred from the presence of indicator-­taxa, it is often important to take a community approach (one that takes all species present into consideration) to the interpretation of a fossil assemblage. This is because it is important to evaluate the role of all species within the community (including considering taphonomic pathways, as previously discussed), rather than ‘cherry-­picking’ individual charismatic species, which may subsequently be given a larger than merited (and erroneous) role in the interpretation. A community approach can be achieved through the use of so-­called indicator groups or indicator packages. Whereas an indicator taxon might be defined as one which reliably carries the implication of the occurrence of some event, activity, or ecological condition in the past, an indicator group often comprise packages of species which are scattered through a wide range of families or orders. This is usually done on the basis of taxonomic (e.g. Dytiscids – indicating aquatic habitats) and functional ecological groups, such as communities of species that live on deciduous or coniferous trees (e.g. Olsson and Lemdahl  2010). From this concept, it is possible to move on to ‘indicator groups’, which collate all biological information with a wide range of other information (sediment, context, archaeology) and can be defined as

a collection of recordable data of any kind, which when occurring together can be accepted as evidence of some past state or activity (Kenward and Hall 1997). These indicator groups are commonly used in the interpretation of a large number of samples from an urban assemblage, leading to the interpretation of samples from ‘stable manure’ (Kenward and Hall 1997), cess and latrine pits (Smith 2013) or representing a ‘house fauna’ (Hall and Kenward  1990; Kenward and Hall 1995). Similarly, groups can be used to identify environmental conditions. Smith (2017) developed beetle ‘indicator groups’ for saltmarsh sediments to facilitate the spatial interpretation of inter-­tidal deposits. Typically, these approaches use statistical ordination approaches to explore the relationship between groups of indicator species and the environmental variable of interest to establish indicator groups. These are cross-­referenced against ecological data. The Modern Analogue Technique (MAT) is an assemblage approach used to quantitatively infer past environmental conditions from a complete fossil insect assemblage. It treats fossil samples in their entirety and aims to find the closest match between the fossil assemblage and a single sample or a set of samples in a modern dataset. The reconstructed value for the fossil sample will then equal the environmental conditions at the modern site(s). The assemblage approach does allow for the calculations of uncertainties but struggles in situations when there are no analogues for the fossil assemblage in the modern dataset, or when there are multiple analogues but with very different environmental conditions. It additionally is sensitive to the fact that different species within one assemblage could be responding to different environmental variables (Birks et al. 2010).

Proxy-­Environment Calibration Approach Finally, the proxy-­environment calibration approach (colloquially known as the transfer function approach) models species responses for individual taxa along an environmental or climatic gradient of interest through estimation of parametric functions. In the first step, a series of sites (e.g. lakes) is sampled along an environmental gradient (e.g. July air temperature). For each site, percent-­abundances are calculated for each taxon. The distribution pattern of each taxon along the gradient is subsequently numerically described using a species-­response model. Numerical modelling can be achieved using linear methods (e.g. partial least squares), unimodal methods (e.g. weighted averaging), or a combination of both. The resulting ‘transfer function’ can subsequently be applied to fossil assemblages to quantitatively estimate past environmental conditions. This approach benefits from the fact that a range of

­Example 

methods are available to calculate uncertainties and error estimates, though several papers have addressed the uncritical application of this approach, showing it can lead to unrealistic values when, for example, unrecognized confounding factors play an important role in determining the composition of the fossil assemblages (e.g. Velle et al. 2010; Juggins 2013). Confounding factors can include any driver that affects the composition of the insect assemblage, but that is unrelated to the environmental parameter being reconstructed. In the case of temperature reconstructions, examples of confounding factors can include changes in the precipitation/evaporation balance, changes in depositional processes, or migration unrelated to climate, such as through the introduction of invasive species. As with most quantitative inference approaches, the method strongly depends on the quality and representativeness of the modern dataset that is used for comparison. Consequently, in non-­analogue situations, these approaches have sometimes been criticized for being unable to fully capture climatic conditions in the past.

­Examples There are many excellent palaeoenvironmental and archaeological studies that use insects as indicators of past conditions. Below we highlight a number of studies that use insects as indicators of past climate and environmental conditions, and as indicators of past lifestyle. We discuss studies that focus on using insects to (quantitatively) reconstruct natural climate dynamics and environmental change, with a specific focus on the last glacial-­interglacial transition, before discussing studies that focus on human populations and their interactions with their environment. The final section of this chapter describes some ways in which insects have been used to reconstruct past lifestyle characteristics.

Insects as Indicators of Past Climate Conditions One of the most important research areas of Quaternary entomology lies in the field of climate change. The discussion of the relationship between past climate fluctuations and human responses through cultural developments, population dynamics, or migration patterns is long-­ standing. Climate parameters that are of interest in these discussions include average summer, winter, or annual temperatures, weather extremes including drought, floods or storms, and freshwater availability. Beetle assemblages have been used to quantitatively reconstructs mean warmest month temperature (TMAX) and mean coldest month temperature (TMIN) using the Mutual Climate Range method. Whilst the use of beetle

fossils as indicators of climate conditions has been carried out most extensively in northern Europe, there are also many important studies from other parts of the world such as North America (Elias  1991,  2015), New Zealand (Marra  2003; Marra et  al.  2004) and Australia (Porch et al. 2009). Subfossil chironomids are often used to quantitatively reconstruct summer temperatures (as average air temperature of the warmest month, often July (Tjul) in Northern Hemisphere-­based studies) using the chironomid-­ climate calibration approach (see above). This technique was first applied to downcore chironomid records in North  America and Europe (Brooks  2006; Walker and Cwynar  2006). Nowadays, chironomid-­inferred temperature (C-­IT) records are available for many parts of the world including Australia (Rees et  al.  2008) and South America (Matthews-­Bird et al. 2016). Quantitative climate records based on both chironomids and beetles records are available on a range of timescales ranging from relatively short timescales, such as those occurring in the last few centuries (e.g. Medeiros et al. 2014), to much longer timescales, such as those focusing on the last interglacial (e.g. Candy et al. 2016; Langford et al. 2017; Plikk et  al.  2019). Specific emphasis has been placed on time periods of large-­scale climate reorganizations such as those associated with the last glacial-­interglacial transition (LGIT, c. 14 500–11 700 years ago) as well as on intervals that have been strongly associated with human impacts and culture, i.e. the present interglacial (Holocene, 11 700 years ago–present). Last Glacial-­Interglacial Transition

The LGIT includes the transitions from the Bølling–Allerød (B–A) interstadial to the Younger Dryas (YD) stadial, and from the YD to the early Holocene, as seen in many pollen records from the northern hemisphere, and reflected in the Greenland ice-­core records as major transitions between stadial (Greenland Stadial-­1; GS-­1) and interstadial (Greenland Interstadial-1; GI-­1) conditions (Rasmussen et al. 2014). As the LGIT is ­characterized by high-­amplitude temperature changes in the mid-­and high-­latitudinal areas of Europe and North America, and the impact of humans on the landscape was still relatively limited, this time window provides an excellent opportunity to test the potential of beetles and chironomids as quantitative indicators of past climate change. A succession of studies in the early 1970s by Coope and co-­workers showed that beetles responded to a series of very rapid climate changes of greater amplitude and speed than had been previously deduced from pollen records (Coope and Brophy  1972; Coope and Joachim  1980; Osborne 1980). A composite curve based on a high number of beetle records provided a complete record of LGIT

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climate change, and this pioneering work showed rapid changes from cold to warm conditions during this period, possibly in less than 50 years during the Younger ­Dryas-­Holocene transition (Coope and Brophy  1972; Walker et al. 1993; Lowe et al. 1999). These inferences of high-­amplitude, abrupt climate oscillations were subsequently confirmed by work on the Greenland ice cores (Dansgaard et al. 1989; Steffensen et al. 2008) and by studies based on independent proxy data, such as those based on chironomids. The first studies to present C-­IT records also primarily focused on the LGIT. Pioneering records such as those from Whitrig Bog in Scotland (Brooks and Birks 2000a) strongly resembled the climate record derived from Greenland ice-­ cores and indicated climate teleconnections across large parts of the North Atlantic region. After initial applications in Canada (Walker et  al.  1991) and Europe (Brooks and Birks  2000a,  b), there are now over 30 chironomid-­based climate records available for the LGIT in Europe alone. Review articles by Brooks and Langdon (2014) and Heiri et al. (2014) provide evidence of abrupt and high-­amplitude changes across the B-­A/YD transition as well as across the YD-­early Holocene transition. The chironomid-­inferred data shows clear evidence for spatial trends in past climate change and are in excellent agreement with global circulation model output (Heiri et al. 2014). Holocene

Several studies have used subfossil beetle remains to reconstruct climate change during the Holocene or as markers of climate change, although understanding Holocene climate changes remains relatively elusive. This is because human impacts may swamp and mask low-­magnitude climatic events. For instance, the presence of fossils of the large saproxylic species Cerambyx cerdo in bog oaks in southern Poland, dated to the Roman period, led Jach et al. (2018) to argue that conditions during the Roman Warm period were more suitable for this species than in more recent times. However, declining availability of suitable high-­quality forest habitat (cf. Whitehouse  2006) is just as likely to have influenced the modern distribution of this species as climatic conditions during the Roman Warm period. To avoid this issue, Osborne (1982) examined the distribution of beetles linked to habitats which are less subject to human disturbance and concluded that there was some supporting evidence that between 4000 and 3000 years ago, summer temperatures were higher than at present, declining to present levels during the Iron Age and remaining more or less constant until the ‘Little Ice Age’. Robinson (2013) argued that slight cooling in mean summer temperatures alongside changing cultivation practices caused the decline and abundance of several dung beetle species by the Roman period.

Beetle fossils helped identify cooling that took place during the Little Ice Age. Forbes et al. (2019) demonstrate that temperatures were significantly cooler in the late fifteenth to late nineteenth centuries ce, impacting native Yup’ik communities in Alaska. Summer temperatures at their study site of Nunalleq were at least 1.2 °C cooler than the modern mean (1983–2016  ce), with coldest periods centred around 1570, 1735, and 1815  ce, after which conditions started to ameliorate. The authors emphasize the importance of palaeoclimate studies that are directly linked to human occupational histories to understand local effects. Cooling related to the Little Ice Age as well as agricultural impacts may also have impacted a number of species found in archaeological deposits from the Norse period in Greenland and Iceland (Forbes et al. 2014). For instance, Hydraena britteni Joy became locally extinct between the fourteenth and fifteenth centuries in Iceland, whilst several other species similarly impacted are identified by Forbes et al. (2014). Similarly, CI-­T records have been produced for Holocene lake sediment sequences across the globe. A recent effort aimed at collating all CI-­T records for the Holocene produced a global overview of c. 80 records (Kaufman et  al.  2020). A summary figure describing global temperature evolution based on averaging of these records shows rapidly increasing temperatures at the onset of the Holocene, highest inferred temperatures in the early to middle Holocene between c. 10 000 and 7000 years ago, and a decreasing trend after that (Kaufman et  al.  2020). Human dispersion and population dynamics from the late Palaeolithic to the present can now be evaluated against local CI-­T records for many parts of the world, providing new opportunities to gain insight into human-­environment interactions.

Insects as Indicators of Past Environmental Conditions There has been a strong tradition of using insect fossils, particularly fossil beetle assemblages, to understand past environmental conditions and biodiversity patterns. In contrast, chironomid subfossils have only more recently been used to infer past human impact on the landscape as well as trends in diversity across a range of timescales. Biodiversity Loss as a Consequence of Woodland Clearance and Land Use Change

Many studies using beetle fossils dating from the mid-­ Holocene onwards highlight the increasing scale and extent of human impact on the landscape. Often, this is represented by a transition from forest-­dominated assemblages to cleared landscape-­dominated communities (termed ‘culture steppe’ by Hammond (1974)) by the later prehistoric period (Smith et  al.  2018), when mature

­Example 

woodland beetle species appear to represent insignificant faunal elements (Osborne  1978; Girling  1982,  1985). Although this story is particularly evident within European beetle communities, quite similar changes are also observed in other parts of the world. For example, Baker et al. (1996) found profound changes in the native insect fauna as a consequence of Euro-­American settlement at a site in Iowa, United States, illustrating the extent to which human activities can destabilize landscapes. What emerges from all these investigations is a major loss of biodiversity of beetle communities over time. Investigations of fossil beetles associated with a Bronze Age trackway on Thorne Moors, South Yorkshire, United Kingdom, revealed an extensive and internationally important beetle fauna associated with undisturbed forest that was characteristic of an Urwaldrelikt fauna – a term often used to describe species which are found in undisturbed, ancient woodland (Buckland  1979). The assemblage included seven species no longer found in Britain (Buckland  1979). Subsequent work by Whitehouse (1997,  2000,  2004,  2006) added many new species to this list of ‘extirpations’ and showed that these important woodland communities survived in refugia such as raised bog systems until later in prehistory but largely disappeared from the British landscape during the Bronze Age. Similarly, work by Reilly, as part of the Lisheen Archaeological Project, Derryville Bog, Ireland, frequently found non-­Irish species such as Prostomis mandibularis (F.) as part of the archaeological record (Caseldine et al. 2001). This species is part of the Urwaldrelikt fauna, living in just a few, more or less isolated, strong points of primary woodland, attacking wood in the final stages of decay (Palm 1959). The fossil beetle assemblages encountered at this site indicate distinct spatial trends across the landscape. On the eastern side of the bog, it seems that primary or sub-­primary woodland survived during the Bronze Age, together with its associated fauna, although some areas appear to have been given over to pasture. On the western margins of the bog, species associated with cultivation, grassland, and dung were evident, and there were no ancient woodland taxa (Caseldine et al. 2001). It is clear, therefore, that in many regions across Britain and Ireland that landscapes were cleared of their primary forest habitats by the late Iron Age and certainly by the Roman period. Beetle fossils from an early Roman well at Dragonby in North Lincolnshire, United Kingdom, indicate a wholly cleared, pastoral landscape with few faunal elements associated with trees (Buckland 1996). The demise of many Urwaldrelikt species has been attributed to the combined loss of undisturbed forest habitats and particularly of dead wood. The apparent poor mobility of many of the saproxylic Urwaldrelikt species may have

played an important part in their decline and extirpation (Buckland and Dinnin 1993), particularly with the onset of forest fragmentation and the loss of continuous forest corridors (Whitehouse  2006). The loss of particular types of woodland, such as pinewood, either through successional competition, decline in forest fires and/or the development and expansion of peatlands, appears to have been an important contributory factor for some species (Whitehouse 1997, 2000, 2006), whilst climate change may also have been a strong causal factor (Dinnin and Sadler 1999; Whitehouse 2006). We, therefore, see a clearly documented major loss of biodiversity as a consequence of human impacts and clearance of woodland habitats for agriculture during prehistory and the historic periods. This is evidenced at many other sites across Britain, Ireland, and elsewhere across Europe. Even in isolated high montane biomes such as the High Tatras Mountains, Slovakia, beetle communities and ecosystems were adversely impacted by anthropogenic and land use changes from about 1000 years ago, changing the composition and diversity of the forest canopy and adversely impacting endemic and montane beetle species’ biodiversity (Schafstall et al. 2020b). The Impact of Prehistoric Settlements on Water Quality

Human impact on the landscape often was direct and intentional, such as through deforestation for agricultural purposes (see above). At other times, human impacts on the landscape were indirect or unintentional: for example, evidence is mounting that prehistoric settlements located on lake shores adversely affected water quality of the lakes. For instance, Taylor et al. (2017) used subfossil chironomid remains as indicators of prehistoric farming impacts on freshwater lake systems in western Ireland. Taylor et  al. (2017) studied three sites and showed that for each locality pastoral farming influenced the lacustrine invertebrate community, favouring eutrophic taxa through increased nutrient inputs resulting from past farming practices. Similarly, Tóth et al. (2019) studied subfossil insect remains (chironomids) and Branchiopoda (cladocera) in lake sediments recovered near Zürich (Switzerland) to assess how periodic settlement phases altered lakeshore environments and aquatic invertebrate communities during the Neolithic. Tóth et al. (2019) identified two separate aquatic communities, one that reflected natural conditions in the lake, and a second ‘impacted’ community reflecting additional organic material and nutrient loading during times of human settlement. Finally, Ruiz et al. (2006) showed that the chironomid assemblages encountered in a lake core from Ballywillin Crannog (Ireland) were impacted by intensification of human activity on the crannog through the introduction of elevated levels of organic detritus,

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wood, and woody debris to the water immediately surrounding the crannog between 1050–1330  ce. Together, these studies confirm that the study of subfossil insect remains can be used to reconstruct localized anthropogenic changes to the environment such as freshwater pollution, and can provide important insight in prehistoric human activities (Tóth et al. 2019).

Archaeological Applications: Insects as Indicators of Past Lifestyle An examination of insect remains preserved within archaeological deposits can provide a wealth of information about the conditions in which people lived, as well as on material related to past lifestyle which has long since decomposed. Many insect taxa encountered in archaeological samples are associated with decomposing matter and are weakly to strongly synanthropic. Synanthropic species are favoured by, or dependent upon, habitats created by human occupation and activity. They form very distinctive communities and beetle remains as well as remains of other insects are encountered, including ectoparasites (e.g. the human flea, Pulex irritans L.), flies (e.g. the house fly, Musca domestica L.), human lice (Pediacus humanus and P. capitis) and many others (Table 10.1). Below we thematically highlight a selection of studies to illustrate the diversity of insect remains encountered in archaeological contexts and their versatile applications. Human Settlements and Living Conditions in and Around Houses

A large number of studies have investigated insect assemblages from structures and settlements from archaeological sites of prehistoric and historic periods. These datasets have enabled a deeper investigation of the origin of many insect communities associated with human habitations, including consideration of the origins of the synanthrope fauna across Britain and Ireland – although for the latter area, the dataset is extremely modest (Smith et  al.  2020). During earlier prehistory, abundances of synanthrope ­species were comparatively low during the Neolithic and Bronze ages and largely consisted of facultative synanthropes – species that occur in the wider environment that were favoured by the enriched ecological conditions on an archaeological site, often occurring in abundance compared with the natural environment. This is likely a reflection of the dispersed nature of human habitations and lack of large settlements during these periods. The development of intensive stock rearing in the Late Bronze age, however, seems to mark a major change in the abundance of synanthropic species, with many facultative and typical synanthropes (species particularly favoured by artificial habitats

but able to survive naturally) becoming dominant in assemblages, including many associated with animal dung and plant litter. These changes are likely a reflection of the intensification of agricultural and pastoral land use (the ‘culture steppe’; see above) (Robinson  2000; Smith et al. 2020). Finally, during the Roman period, we see the importation of grain and other traded goods due to the expansion of Roman maritime trade, with the arrival of exotic synanthropes from the empire and insect communities that are strongly synanthropic, i.e. species that are dependent on human habitation for survival (Smith et al. 2020). These insect communities are associated with urban settlement and increasingly interlinked communities, a trend that accelerated and continued into the historic period. Very good examples of investigations focused on these urban communities are offered by studies associated with Viking settlement sites. Reilly (2014,  2016) summarizes evidence from ninth century ce Dublin, which provides detailed insights into Viking house plots and how the settlement grew increasingly in a dense fashion through the tenth and eleventh centuries (Coope  1981; Reilly 2014, 2016). Beetle remains indicate that buildings used thatching, sod and turf as building materials, with living conditions likely to be warm if somewhat damp. In contrast, investigations of Viking deposits at Novgorod, Russia, highlight very different building materials used in house construction (Reilly 2016), including the use of pine and spruce, as indicated by insect pests of these timbers. House floors initially covered with sand and gravel or sod were then covered with regularly replenished plant matter. Well-­preserved floor layers show that floors were frequently covered with a mass of decomposing and fermenting vegetation, carrion and faecal matter and other detritus of life, thereby providing habitats for a wide range of invertebrates. Large numbers of flies and lice were found, especially from aisle and bedding areas, but it is clear that central floor areas had more in common with yard and pit deposits, likely the result of narrow, densely-­packed house plots and lack of paths that meant constant movement to the centre of the house (Reilly 2014). Animals were kept in plots associated with each house, mostly pigs, goats, and sheep (Reilly 2016). The entomology of Norse sites in the North Atlantic has been pioneered by Buckland et al. (1994, 1996) and colleagues (Skidmore 1995). Their work on beetles, parasites, and flies from Norse Greenland and Iceland really established the value of insect synanthrope remains for reconstructing past activity and living conditions on North Atlantic farmsteads, work that has been considerably extended by a range of researchers (e.g. Forbes et al. 2014). This research has facilitated an understanding of local

­Example 

resource exploitation, especially the use of turf in buildings, peat for fuel and litter, the use of vegetation for roofing and flooring purposes and the importance of fodder for over-­wintering animals. Ethnographic records suggest that seaweed was also used as a source of salt, animal feed, fertilizer, bedding, and fuel, whilst insects associated with marine littoral zones imply the exploitation of these areas, perhaps the consequence of seaweed collection and storage (Forbes et  al.  2014). The recovery of the duck flea, Ceratophyllus garei Rothschild, in abundant numbers alongside eggshell fragments, feathers, and other plant materials from floor layers from the eighteenth century ce in northwest Iceland suggest eiderdown production activities (Forbes et al. 2014). Many of the ectoparasites (e.g. Pulex irritans) and flies encountered in floor layers from Viking York, Dublin, Oslo, and a number of Icelandic and Greenland sites were vectors of significant diseases such as typhoid, cholera, and tuberculosis that severely impacted populations in the past. Finding evidence of such disease vectors offers considerable insights for the understanding of disease transmission and development (Panagiotakopulu and Buckland 2017). Living conditions at these Norse sites were not uniformly foul or unpleasant, although ectoparasites associated with ­bedding areas likely indicate some level of discomfort (Reilly 2016) and may well have carried the ongoing risk of disease. Pests and Commodities

The story of insects associated with human activities emphasizes the huge role of humans in introducing insect pest species to different parts of the world through shipments. The arrival of the Norse settlers in Iceland and Greenland played a significant role in modifying the distribution and frequency of some native species and the introduction of many others. The arrival of several important insect synanthropes, dependent on the artificial warmer conditions within houses and ancillary buildings, was a direct consequence of Norse colonization and encouraged the expansion of many native species at settlement sites, which mimicked nutrient-­rich natural settings. The common presence of the grain weevil, Sitophilous granarius (L.), and the saw-­toothed grain beetle Oryzaephilus surinamensis (L.) in these settings was likely the consequence of the importing of grain from abroad (Buckland et al. 1996). Pests associated with stored products increased over time as communities increasingly turned to crop food production. The Neolithic spread of agriculture to Europe is ­associated with an increase in granary weevil Sitophilous granarius remains, for example, from the Neolithic lake settlement of Dispilio, in Macedonia (northern Greece), dated to 5780–5720  bce (Panagiotakopulu and Buckland  2018). The species is not native to the region and has its origins in

the Fertile Crescent, perhaps originally in the nests of rodents (Panagiotakopulu and Buckland 2018). The weevil infested grain as early farming communities developed bulk storage systems. Its presence at Dispilio indicates significant storage (and surplus) of grain. The species also occurs in several central European Linearbandkeramik (LBK) Neolithic sites over the following millennium (Panagiotakopulu and Buckland 2018), moving north with agriculturalists. Another species that seems to have been introduced with early agriculture is the common house fly, Musca domestica, which may have had an origin in the Nile valley. By 3500  bce, it had reached northern regions of Europe, presumably travelling north with farming communities and their animals and finding suitable habitats in settlements and animal stalls (Panagiotakopulu and Buckland 2018). The importance of these records is not just around what they imply around the movement of people, but also, in the case of Sitophilous granarius, what its presence implies around the scale of grain storage and surplus during the fifth millennium bce. Antolín and Schäfer (2020) report evidence for ongoing pests in pulse crops from the fifth and fourth millennia bce, with evidence for pea weevil infesting Vicia faba (fava beans) in the NE Iberian Penisula (c. 4800–4500 bce) and Pisum sativum (peas) in Central Switzerland c. 3160 bce. Pests might have affected pulse crops in central and southern Europe on an ongoing basis during the Bronze and Iron ages; the use of companion plants may have been one strategy used by farming communities to control pest attacks (Antolín and Schäfer 2020). Companion plants are cultivated plants that are planted alongside the plant of economic interest to keep pests at bay; it is a common strategy in organic farming and gardening practice today, for example, to keep pests and diseases under control. It was not until the Roman period, however, that insect pests associated with stored products become widely distributed (Buckland 1981). At this time, the provisioning of numerous legionary and auxiliary units, each consisting of between 500 and 5000 men, required large-­scale transport of foodstuffs, particularly during periods of active campaigning, and also the construction of large granary structures. At Mons Claudianus, Egypt, a Roman fort associated with quarrying, Panagiotakopulu and Van der Veen (1997) found pests suggesting the import of processed food commodities, such as flour and other milled products. The site represents a unique record of dispersal of insects associated with stored products dependent upon trade to a remote desert situation. Fragments of locusts were also recovered, which were interpreted as the remains of food. Finally, the study of insect material from desiccated environments has considerable potential, as evidenced by the

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recovery of a Bronze Age silk cocoon, from Santorini (Thera), Greece, suggesting silk production at this early date in the Mediterranean (Panagiotakopulu et  al.  1997). The cocoon was calcified with part of the enclosed pupa and was associated with finds of mid-­second millennium bce date, suggesting the presence of wild silk in the Aegean. Thera has plentiful evidence for its involvement in textile manufacture and trade, and there appears to be enough other evidence – pictographic and literary – to suggest that silk played an important part at this site. This example illustrates the use of commodities which would otherwise pass unnoticed in the archaeological record.

­Conclusions and Future Potential Much progress has been made since the first studies of subfossil insect remains within a palaeoenvironmental framework were published at the end of the nineteenth century and early twentieth century (e.g. Flach 1884; Bell 1922), or even since the publication of the chapter on ‘Insects as Palaeoenvironmental Indicators’ in the previous edition of this book (Robinson  2001). For instance, recent developments include improvements in taxonomic resolution, as well as the development and application of a suite of new numerical techniques that enable quantitative palaeoenvironmental reconstruction. New fields of application are continuously being developed, including but not limited to insect-­based biodiversity reconstructions, analysis of the origins of the synanthropic fauna, or studies of past outbreaks of diseases. The development and application of such new approaches will continue over the coming decades. One exciting prospect that will further inform on climate change through the entomological record are sedimentary aDNA (sedaDNA) studies (see Chapter 12 and Section 10.4). This novel technique allows the isolation and identification of fossil DNA-­strands from lake, peat, and archaeological sediments and produces records of past local occurrences of plants or animals at unprecedented taxonomic resolution, often reaching species level. Application of sedaDNA analysis to studies of subfossil insects will revolutionize the field as it circumvents issues related to identification based on small fragments of insect exoskeletons and allows species-­level identifications, even for groups or families that normally do not leave micro-­ or macroscopically visible remains behind in palaeoenvironmental or archaeological contexts. Additionally, analytical capacities of laboratory equipment are allowing increasingly smaller amounts of material to be analyzed for their stable isotope ratios (Holtvoeth et  al.  2019), including the analysis of chitinous remains (Van Hardenbroek et  al.  2018). Oxygen isotope ratios

derived from insect remains can inform us about changes in their past physical environment, including past temperatures (Verbruggen et al. 2010). Carbon isotope ratios can also reflect environmental conditions such as changes in land use or eutrophication, but they can also inform on changes in food source (Van Hardenbroek et  al.  2018), opening up the potential to analyze changes in ecosystem structure through the analysis of the stable isotope composition of subfossil insect remains derived from groups with different feeding styles (e.g. filter feeders, predators). However, Van Hardenbroek et al. (2018) describe the challenges in this approach caused by the absence of reliable estimates of stable isotope of dietary components such as algae, bacteria and allochthonous organic matter. Finally, analysis of other stable isotope ratios (H, N, S) contained in subfossil insect material is gaining traction as analytical techniques continuously improve. The general premise for evolutionary stasis generally holds true for assemblages associated with environments that would have been subjected to rapid climatic changes in the past, but may be less true for communities at lower latitudes, such as the tropics, where there has been very little research (and would merit research attention). Other regions where there has been extended genetic isolation such as high endemic areas such as New Zealand would also merit additional studies, to understand the role of ­isolation on biodiversity and evolutionary traits of insects, although several fossil beetle studies support species persistence over the early-­middle Quaternary (Marra and Leschen  2011). There is a demonstrable bias in the fossil evidence that we have amassed to date: the majority of Quaternary fossil records are from the late glacial and Holocene periods, from north-­western Europe, where evolutionary stasis is a more likely scenario than evolution (Abellán et al. 2011). Evidence from the Iberian Peninsula (Ribera and Vogler  2004), America (Barraclough and Vogler  2002), and New Zealand (Pons et  al.  2010) has shown that in these refugial regions climate-­change induced isolation may have been more important in driving niche change and species radiations, as opposed to stasis. There is little published fossil evidence from potential ‘refugial’ sites (e.g. Panagiotakopulu and Buckland  1991) which makes fossil corroboration of phylogenetic evidence of radiations difficult to ground-­truth. This highlights the need to improve understanding of the role of glacial refugia in driving the evolution of beetles in the Pleistocene. One way in which this could be explored is through the use of niche models such as Species Distribution Models (SDMs) to understand how functional niches have remained stable through time (e.g. Araújo and Luoto 2007; Zimmermann et al. 2010). Identifying changes in insect morphometrics over time may hold important information on species traits and their

 ­Reference

relationship to local environment and climate conditions and potential avenues for future research. For instance, Schweiger and Svenning (2018) examined the temporal trends of dung beetle size and demonstrated a significant decrease in beetle body size over the last 53 000 years, a trend that mirrored the decline and extinction of the megafauna. Shifts in beetle size were especially marked at the end of the Quaternary, coinciding with megafauna extinction processes and again at c. 4300 BP associated with major shifts in land use linked to agriculture during the Neolithic in Europe. Dung beetle sizes are also related to dung patch size, so the down-­sizing of dung beetles across the last 53 000 years is likely related to the decline of dung patch sizes as a result of the loss of large herbivores and impoverishment of large mammal communities. The work by Schweiger and Svenning (2018) demonstrates the value of using the fossil record in combination with trait-­based approaches to understand the ecological effects of extinctions, species declines, and that of anthropogenic activities in more recent times and points towards new research directions in understanding past food webs on millennial to centennial timescales. Finally, there is a pressing need for more archaeologically focused investigations of entomological materials outside of northern Europe. Many of our current

understandings of houses, settlements, and urban areas, as told from their entomology, comes from a limited geographic area and are consequently limited in terms of what they can contribute to wider discussions around the intimate details of urbanization, the changing and symbiotic relationships between humans, insects and pests and the rise of disease. There is a need for further investigations to focus on waterlogged and organic-­rich deposits of central and southern Europe and the Mediterranean, whilst investigations from the Middle East, and along the Silk Route to China, as corridors for the movement of trans-­Eurasian, trans-­continental commensurals (cf. Liu and Jones 2014), would likely yield dividends. Evidence for the deep human prehistory of tropical environments (e.g. Roberts et al. 2017) suggests that, under the right preservation conditions, investigation of the fossil insect record of, for example, Mayan urban complexes and agricultural groups in the Amazonian basin that were decimated by the arrival of Europeans (cf. Koch et al. 2019), would likely offer exciting new avenues for research. Such work could revolutionize our understanding of these societies and human-­insect relationships in the past. More broadly, this would allow researchers to produce globally significant accounts of our symbiotic and changing relationships with insects in the past.

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Väliranta, M., Birks, H.H., Helmens, K. et al. (2009). Early Weichselian interstadial (MIS 5c) summer temperatures were higher than today in Northern Fennoscandia. Quaternary Science Reviews 28: 777–782. Van den Bos, V., Brinkkemper, O., Bull, I.D. et al. (2014). Roman impact on the landscape near castellum Fectio, The Netherlands. Vegetation History and Archaeobotany 23: 277–298. Van Hardenbroek, M., Chakraborty, A., Davies, K. et al. (2018). The stable isotope composition of organic and inorganic fossils in lake sediment records: current understanding, challenges, and future directions. Quaternary Science Reviews 196: 154–176. Velle, G., Brodersen, K.P., Birks, H.J.B., and Willassen, E. (2010). Midges as quantitative temperature indicator species: lessons for palaeoecology. The Holocene 20: 989–1002. Verbruggen, F., Heiri, O., Reichart, G.J. et al. (2010). Effects of chemical pretreatments on δ18O measurements, chemical composition, and morphology of chironomid head capsules. Journal of Paleolimnology 43: 857–872. Walker, I.R. and Cwynar, L.C. (2006). Midges and palaeotemperature reconstruction – the North American experience. Quaternary Science Reviews 25: 1911–1925. Walker, I.R., Mott, R.J., and Smol, J.P. (1991). Allerød– Younger Dryas lake temperatures from midge fossils in Atlantic Canada. Science 253: 1010–1012. Walker, M.J.C., Coope, G.R., and Lowe, J.J. (1993). The Devensian (Weichselian) lateglacial palaeoenvironmental record from Gransmoor, East Yorkshire, England. Quaternary Science Reviews 12: 659–680. Whitehouse, N.J. (1997). Insect faunas associated with Pinus sylvestris L. from the mid-­Holocene of the Humberhead Levels, Yorkshire, U.K. In: Studies in Quaternary Entomology – An Inordinate Fondness for Insects (ed. A.C. Ashworth, P.C. Buckland and J.P. Sadler), 293–303. Quaternary Proceedings 5. Chichester: Wiley. Whitehouse, N.J. (2000). Forest fires and insects: palaeoentomological research from a sub-­fossil burnt forest. Palaeogeography, Palaeoclimatology, Palaeoecology 164: 247–262. Whitehouse, N.J. (2004). Mire ontogeny, environmental and climatic change inferred from fossil beetle successions from Hatfield Moors, Eastern England. The Holocene 14: 79–93. Whitehouse, N.J. (2006). The Holocene British and Irish ancient forest beetle fauna: implications for forest history, biodiversity and faunal colonisation. Quaternary Science Reviews 25: 1755–1789. Whitehouse, N.J. and Smith, D.N. (2010). How fragmented was the British Holocene wildwood? Perspectives on the “Vera” grazing debate from the fossil beetle record. Quaternary Science Reviews 29: 539–553.

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International Symposium on Trichoptera, Series Entomologicae 30 (ed. J.C. Morse), 447–452. The Hague: W. Junk. Zimmermann, N.E., Edwards, T.C. Jr., Graham, C.H. et al. (2010). New trends in species distribution modelling. Ecography 33: 985–989.

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11 Mammals as Palaeoenvironmental Indicators Julien Louys1 and Hannah O’Regan2 1 2

Australian Research Centre for Human Evolution, Griffith University, Brisbane, Queensland, Australia Department of Classics and Archaeology, University of Nottingham, Nottingham, UK

Mammals are animals in the Class Mammalia, identified by the presence of three bones in the inner ear (the auditory ossicles; malleus, incus, and stapes), milk-­producing mammary glands, and a covering of hair or fur on their bodies (Wilson 2009). Mammals come in many shapes and sizes, from blue whales to pygmy shrews, and are able to live in a wide variety of habitats, from the polar regions to arid deserts and the open oceans. They also have a wide range of evolutionary adaptations to these habitats, such as the loss of hind limbs in whales, the development of the forelimbs into wings in bats, and the reduction in the number of digits in bovids and equids (Wilson 2009). This wide variety of morphologies and habitats makes them excellent palaeoenvironmental indicators as long as the archaeological or fossil remains can be identified. Archaeological and fossil mammal remains are usually found as either bones or teeth. Teeth are more resistant to density-mediated attrition and diagenesis in the burial environment as enamel is approximately 97% mineral (Ungar 2015). Bone in contrast contains a high proportion of organic collagen, which is more readily decayed by microbial activity. Teeth are also particularly useful for identifying animals to genus or species (see section on  Taxonomic Identification, Uniformitarianism, and Autecology). Bones retain interesting information about the evolutionary history of an animal as a species and as an individual (e.g., how many toes is an evolutionary question, while the identification of pathologies is particular to that specific animal). However, other remains of mammals are occasionally found in archaeological settings. These include soft-­tissue preservation in very arid, cold, or saturated regions (sometimes referred to as ‘mummified’), such as the dried remains of a thylacine from Nullarbor cave in Australia (Partridge 1967) and the frozen remains of woolly

mammoths and steppe bison in the permafrost of Siberia and Alaska (Guthrie 1989). These soft tissues can tell us an enormous amount about these creatures as individuals as well as providing data on diet (from stomach contents), external appearance (e.g. coat length and colour), and behaviour, such as use-­wear on woolly rhino horns indicating they were used for snow clearing and lion predation evidence on the carcass of a bison (Guthrie 1989). Indirect evidence is also found and includes footprints, coprolites, and middens. Footprint trails can retain information about social groupings (such as the famous Laetoli hominin footprints; Hatala et  al.  2016), but they can also reflect the make-­up of the local faunal community, as the surface in which the footprints are laid down is often exposed for only a short period of time. For example, footprints in intertidal silts from Formby in North West England have been identified as human, auroch, domestic cattle, crane, red deer, and roe deer, giving a clear indication of the taxa that were using the shoreline in the Neolithic and Bronze Age (Huddart et  al.  1999). Coprolites are preserved faeces and are occasionally found in waterlogged or arid environments. They provide direct evidence for an animal’s diet, as food remains such as seeds or bone fragments can be identified in the scat (see Chapter 38). They are also potential sources of information about parasites, such as intestinal worms, and the DNA of both the animal that excreted them, and the food that they have eaten (Horne  1985; Wood et  al.  2012,  2013). Finally, animals such as rock hyraxes (dassies) repeatedly defecate and urinate in the same location, while packrats collect plant material to make their nests. Both can build up large middens over decadal (pack rats) to millennial (hyrax) scales. Studies of hyrax middens in Southern Africa have enabled scientists to look at changes in palaeoclimate and vegetation through the study of stable

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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isotopes (δ15N, δ13C), pollen, lipids, microcharcoal and phytoliths (Chase et al. 2012). However, like soft tissue preservation, indirect evidence such as footprints and middens are only found in very specific environments, while body fossils are often more widely distributed. Mammalian fossils are often divided into two groups  – microfauna or small mammals (small rodents, bats, etc.) and macrofauna or large mammals (usually badger-­sized and upwards). Each comes with its own advantages and disadvantages for study. Often the study of small mammals has lagged behind that of the larger species for two reasons. Firstly, there are many more microfaunal taxa, which often require microscopes, detailed measurements, and/or genetic information to tell them apart; secondly, until relatively recently, sites were not routinely sieved and therefore many small bones were not recovered for study. An advantage of microfaunal assemblages is that when they are found, they are often in large quantities, such as the ‘frog earth’ made up of large numbers of amphibian and small mammal bones found in concentrated deposits in cave environments (O’Connor and Lord  2013). Large quantities such as these can be used, with or without statistical analysis, to identify habitats quite precisely, as small vertebrates usually have a limited home range or habitat range, and thus the variation between species through time can potentially chart changing local environments (Blois et al. 2010). Taphonomy has to be considered here since if the small mammals have been collected by a predator, then selection may have taken place (Fernández-­Jalvo et  al.  2016). In contrast, large mammal bones are frequently found in burial environments, but owing to the large home ranges of many large mammalian taxa, their identification at a specific site may not necessarily indicate anything about the composition of local habitat. For example, female African elephants (Loxodonta africana) in the Kruger National Park move a minimum of 4 km/day through both open grassland and tree cover (Marston et  al.  2020), while migratory animals such as reindeer or ­wildebeest may move hundreds of kilometres in a year. Some of the major factors that should be taken into ­consideration when attempting to interpret archaeological and palaeontological assemblages to better understand paleoenvironment include geochronology, (i.e., establishing the probable age of the deposit and the fossils therein), the spatial extent of any excavation undertaken, in terms of both depth and area, and taphonomic processes that can be both an agent of destruction as well as a source of valuable environmental evidence.

­Taphonomy Taphonomy concerns the processes involved in the transition between the biosphere and the geosphere. The study

of taphonomy has traditionally been focused on measuring and determining the loss of biological material as it becomes incorporated into the geological record. The impetus behind such studies is to understand taphonomic processes and thereby determine biases present in faunal records and past ethologies. For archaeological deposits, the latter aim is often central to zooarchaeological studies, as taphonomy can provide unparalleled insights into understanding ancient human behaviour. However, the study of taphonomy need not be a study of net losses of a faunal assemblage. Taphonomic analyses can provide an important source of palaeoenvironmental information. In many respects, taphonomic analyses bear more than a striking resemblance to sedimentological studies (Wilson 1988). Many taphonomic variables record the impact of environmental agents such as weathering, hydrological sorting, and wind abrasion on a bone deposit, providing important concurrent environmental insights (Giusti et al. 2019). Site type and the mode offaunal bone accumulation must also be considered – for example, the presence of fossils in South African caves may be the result of overland water flow, predator accumulation, or denning/roosting behaviour, and, careful study is required to tease these possibilities apart (Brain  1981). In addition, hominin behaviour may alter the palaeoecological signal found in mammalian assemblages. At Azokh cave in the Caucasus (as summarized by Fernández-­Jalvo et al. 2016), hominins were hunting large mammals in the wooded regions close to the site, while the European eagle owl was hunting small mammals and amphibians in open areas some kilometres away. This could have led to two different palaeoenvironmental interpretations if only one of the assemblages had been examined. A further consideration is the type of site itself. Sites can be divided into open air or closed sites, and each will attract, accumulate, and disgorge fossils in a different way. For example, an East African open site may have fossils eroding from the sediments onto the land surface. The survival of these fossils for study can often be a matter of luck, and someone seeing them before they are eroded in the sub-­aerial environment. In the South African cave sites, remains can be encased in a very hard matrix comprised of sediment and calcium carbonate from the surrounding rocks. This can erode into softer sediment (called decalcified breccia), while that which is still calcified requires acid solutions, physical abrasion with microscribes, explosives (now rarely used), or CT scanning and 3D reconstruction to find and identify the remains encased within the rock. Thus the fossils recovered, and their ­condition, is very much dependent on their taphonomic histories (see Chapter 56 for the taphonomy of human bone). Taphonomy can also indicate the presence and taxonomic identity of species that may not otherwise be represented in

­Taphonom 

faunal assemblages (Behrensmeyer and Kidwell  1985). One  of the earliest and probably the most widely applied use of such data relates to the identification of carnivores in deposits from the feeding traces they leave on prey animals (Haynes  1983). In some instances, taphonomic data can provide further biological insights into mammalian carnivores, such as denning behaviour, that have obvious environmental implications (Palmqvist and Arribas  2001). Another group of mammals that may be easily identified from the marks they leave on bones are rodents. Porcupines are particularly voracious consumers of bone, especially in Southeast Asia (Louys et al. 2017), where they often gnaw elements down to tooth crowns leaving distinctive parallel spatulate groves. Porcupines also carry remains back to their lairs to gnaw, and the signature of a Cape porcupine (Hystrix africaeaustralis) lair is different to that of lairs occupied by multiple taxa, or fossil deposits accumulated over a long period of time (O’Regan et  al.  2010). Other traces, such as trampling marks, could indicate the presence of large or hoofed animals on the landscape.

Case Study: Cooper’s Cave Cooper’s Cave, Gauteng, is a typical South African hominin-­bearing site. Originally formed as a series of ­cavities within the dolomitic limestone (there are three fossiliferous localities currently identified – A, B, and D), the caverns filled up with breccia during the Pleistocene. The

best-­studied and dated locality is Cooper’s D, which contains a wide variety of taxa including carnivores, antelope, primates, and suids (de Ruiter et al. 2009), and is modelled to date between 1.32 and 1.41 Ma (Pickering et  al.  2019). Like many nearby sites such as Sterkfontein and Swartkrans, the site of Cooper’s D has been considerably eroded over time, with the cave losing its roof and much of the fossiliferous deposit from the interior (Brain 1981, de Ruiter et al. 2009; see Figure 11.1). Some of the remaining fossiliferous deposits have been decalcified, and it is this material that has received the majority of the study. As it is the material at the bottom of the cave that has been discovered, it contains a somewhat winnowed assemblage and, particularly noticeable in the case of the carnivores and primates, it is dominated by isolated teeth and foot bones (Val et  al.  2014, Kuhn et  al.  2017, O’Regan and Steininger 2017). However, if calculated in relation to the number of elements expected per individual, primate foot bones are under-­represented (Val et al. 2014). A somewhat similar assemblage dominated by adult human teeth and phalanges was seen in the lower levels of a Romano-­British cave deposit from Cumbria, England, where the bones had likely travelled with water or through voids between clasts to be re-­deposited below (O’Regan et  al.  2020). This suggests that similar processes operate in caves in very ­different environments, periods, and regions. A key question when considering cave deposits is the potential accumulator of the bone assemblage and the

Figure 11.1  Dr Christine Steininger (right, Site Director) and Dr Hannah O’Regan (left), examining the Cooper’s D locality, in Gauteng, South Africa. The brown area in the foreground is in situ fossiliferous breccia, while the open areas contained decalcified breccia and have subsequently been excavated. Source: Photo credit: Dave Wilkinson.

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palaeoenvironments that their accumulations might indicate. This is in addition to the potential for animals to deposit themselves in caves, even those that may seem to be unlikely cave-­frequenters. For example, Bountalis and Kuhn (2014) identified multiple taxa visiting four South African caves over a one-­month period. These included warthog, kudu, and sable antelope, which, if found in archaeological deposits, would be likely to have been identified as having been transported there rather than visiting voluntarily. At Cooper’s D, multiple potential accumulators are present, including three hyaena taxa whose modern conspecific or congeners are known to collect bones (Crocuta ultra, brown hyaena, and striped hyaena; Kuhn et  al.  2017), leopard (O’Regan and Steininger  2017) and Cape porcupine (de Ruiter et al. 2009). A detailed taphonomic study of the primate assemblage found that the overall rarity of carnivore modification and the age structure of the primate remains suggested that the primates had been occupying the cave rather than being predated (Val et al. 2014). In contrast, the high number of small carnivore species present (Cohen et  al.  2019; O’Regan et  al.  2013) and the presence of hyaena coprolites (Val  et  al.  2014) indicated that brown hyaenas may have collected these remains, although the possibility of accumulation by large predatory birds cannot yet be excluded (Cohen et al. 2019). This example demonstrates that there are often multiple sources for bones within a site, and each may have contributed their own signature to the assemblage. The mongooses were particularly helpful in identifying the local palaeoenvironments, as the presence of marsh mongoose indicates streams or marshy ground within 1–2 km of the site, and banded mongoose remains suggest a bushy or more wooded habitat (Cohen et al. 2019).

­ axonomic Identification, T Uniformitarianism, and Autecology The first point when considering palaeoenvironmental reconstruction from faunal remains is the identification of those remains to a taxonomic group. In most instances, this is done through the examination of gross morphological features preserved in the bones found in deposits. In an ideal case, taxonomic identification is made through direct comparisons with a species’ holotype – the name-­bearing specimen that defines that species. However, this is rarely achievable. Holotype specimens may be undefined, lost, or difficult to access. More often, however, the fragmented nature of many archaeological assemblages means that species-­specific morphological characteristics (autapomorphies) will not be preserved. Identification may be made only to higher-­level taxonomic ranks, for example genus or

family. This becomes more acute for extinct fossil species whose holotypes are rarely represented by entire skeletons. In these instances, the name-­bearing type is often one element, with teeth being particularly useful (and thus common) for discriminating mammals. While gross anatomical comparisons will provide most identifications, other techniques are being increasingly used, often in combination. For example, the use of mass spectrometry and ancient DNA in archaeology to identify bone fragments is becoming more common as cost and destructiveness decreases, and technological precision increases (e.g. Birch et al. 2019; McGrath et al. 2019). Because of the hierarchical nature of the Linnaean classification system and its relationship to environmental resolution, taxonomy provides a hierarchical insight into palaeoenvironments and is scale sensitive, in much the same way as time and space (Bennington et al. 2009). In general, the better the taxonomic resolution of a specimen, the better the palaeoenvironmental inferences that can be drawn from the presence of that taxon. This is because, ecologically, animals divide up a landscape and its resources such that they minimize overlap with any competing animals (competitive exclusion). This is most clearly observed at the species level, although other levels of niche separation are also sometimes observed, for example at the intraspecific level. Nevertheless, some suprageneric groups have been widely used in archaeology to reconstruct environments. For example, Vrba (1980) found that the bovid tribes Antilopini and Alcelaphini were found in higher proportions in African open game parks and reserves. She established the Antilopine-­Alcelaphine Criterion (AAC) to reconstruct palaeoenvironments in Pleistocene South African sites, whereby the presence of these tribes in high proportions was used as an indicator of the presence of open environments. Autecology is the study of a single species, which can then be used to reconstruct environments. At its simplest, it examines one or several functional traits of a species, or the habitat preference of a species, and projects these into the past. Examples of functional traits that are useful and informative for palaeoenvironmental reconstruction include diet and locomotion, as these are intimately associated with habitats  – arboreal browsers will be found in association with trees while grazing quadrupeds will be found in grassy environments. For certain mammals, their unique and restricted habitat requirements make them ideal for environmental hindcasting. For example, koalas have diets restricted to eucalyptus leaves, and thus their presence in deposits in the Nullarbor Plains indicates the presence of sclerophyll forests of sufficient density to support populations during the Pleistocene (Price  2012). However, the current ranges and habitat preferences of a species may not be indicative of their past behaviours or

­Taxonomic Identification, Uniformitarianism, and Autecolog  215

Case Study – Gongwangling, China The Early Pleistocene site of Gongwangling, Lantian County, Shaanxi Province, China provides a useful case study on the use of taxonomic uniformitarianism in palaeoenvironmental reconstructions and how these can shed light on biogeography and palaeoecology. Gongwangling is the site of the oldest hominin specimen in China. In 1964 a cranium attributed to Homo erectus was recovered in a layer attributed to loess – a sedimentary environment characterized by the accumulation of wind-­blown silts (Jia 1965). Gongwangling is located on the northern side of the Qinling Mountains, and the loess layer attributed to the site is part of the Chinese loess-­palaeosol sequence of the Loess Plateau. This sequence formed during glacial-­ interglacial conditions, with loess deposits associated with cooler and drier periods, and paleosol deposits indicating warmer and moister periods (Zhu et  al.  2015). A diverse mammalian fauna was recovered alongside the hominin cranium from carbonate concretions (An and Ho 1989). The fossil deposits were initially correlated with either the upper sandy loess L9, dated to 0.78 Ma, or the lower sandy loess L15, 1.09–1.2 Ma, of the Luochuan Sequence (Liu et al. 1985), with subsequent work reinforcing the L15 correlation (An and Ho 1989). This implied that the fauna and hominin lived in the cool, dry conditions associated with loess formation. However, the mammalian fauna from the site indicated very different environmental conditions. This was recognized very early on in the history of the site. Palaeontologists Chow and Li (1965) and Hu and Qi (1978) highlighted the recovery of many mammalian species from Gongwangling that are typically associated with the warmer and more moist conditions of Southeast Asia. They used the presence of indicator species such as tapirs, snub-­nosed monkeys, and tigers to reconstruct the environment as a subtropical forest, a reconstruction supported by fossil pollen data (Hsu 1966). Louys et al. (2009) took this qualitative analysis one step further. They examined the proportion of species falling into 24 common mammalian families as a quantitative basis for reconstructing the environment of Gongwangling. As a first step, they compiled species lists from a range of East and Southeast Asian protected areas  – essentially presence/absence data. From these, they were able to calculate the proportion of species that were present in each of the 24 families for each protected area. Each ­protected

area was also assigned to one of three habitat categories – closed forests, mixed environments, and open areas. They demonstrated that the species proportions in these protected areas grouped according to these habitat types using a cluster and principal components analysis. These habitats also exhibited strong biogeographical patterning (Louys et al. 2009; see Figure 11.2). They then calculated the proportion of Gongwangling fossil taxa falling into each family and, using a discriminant functions analysis, classified what sort of environment Gongwangling most likely represented. This multi-­species taxonomic uniformitarian analysis supported the initial interpretation that the Gongwangling mammals lived in a subtropical forest. Thus, although today Gongwangling is found in northern China – an area considered zoogeographically and climatically distinct from the warmer and more humid south, during the Early Pleistocene Gongwangling was much warmer than today. A later reanalysis of the stratigraphy and geochronology of Gongwangling indicated that there was a stratigraphic hiatus in the section from which the fossils were recovered. It is now accepted that the deposit lies in a palaeosol (dated to c. 1.54–1.65 Ma: Zhu et al. 2015) rather than loess, consistent with both the qualitative and quantitative mammalian palaeoenvironmental reconstructions.

25 20 Open

15 Component 2

preferred environments. Thus, ecological uniformitarianism as a tool for palaeoenvironmental reconstruction should be used with caution, particularly for older deposits, or validated through independent means such as stable isotope analysis.

10 5

Gongwangling

0

Mixed

–5 –10 –15 Closed –20 –50

–40

–30

–20 –10 0 10 Component 1

20

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Figure 11.2  Principal component analysis of modern Asian mammalian communities and the Early Pleistocene site of Gongwangling. Data from Louys et al. (2009), tables 2 and 4. Open communities are shown in red, mixed communities in light green, and closed communities in dark green. Input variables were rounded off percentages of species found in each mammalian family in each community. The fossil site clearly clusters with other closed forest communities.

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­Morphometrics

­Body Size

A critical part of the palaeontological process has been measuring specimens. Traditionally this was done using Vernier or digital callipers to measure to the nearest 0.1 mm. However, over the last 25 years, Geometric Morphometrics (GMM) have come much more to the fore, and these allow specimen shape and size to be recorded in multiple dimensions. For 2D specimens, or those with low relief, photographs are commonly taken, and the specimen is digitized directly from photographs. For 3D specimens such as skulls, data can be collected directly using a microscribe or scanned using a computed tomography (CT) scanner. A cheaper method that requires much less equipment is photogrammetry, where specimens are photographed from multiple positions, and the photographs are stitched together to create a digital 3D model that can then be measured and interrogated. Each of these methods moves beyond the simple methods of measuring from A to B and allows the capture of 3D coordinates, as well as the quantifiable definition of slopes, angles, or curves (Zelditch et al. 2004). Morphometrics provide the key underpinning for ­calculations of body size. The measurements that are captured can be used to compare the size of the animals within a particular site  – to determine if there are different-­sized but similar-­looking species present, or if there is sexual dimorphism within a species (in mammals, the males are often larger than the females, although in other animals such as birds this can be the other way round). If fossil remains can be sexed, then this can inform us about social behaviour, e.g. whether or not that species was living in mixed-­sex groups. Comparisons between sites or between different layers within sites can show spatial or temporal differences, such as whether species have become larger through time – the increase in encephalization in hominins is a good example of this (Shultz et al. 2012). While morphometrics still play an important role in identification and comparison of remains, increasing numbers of more sophisticated methods have been developed for this, including morphological and metric comparisons of teeth using microtomography (e.g. 2D: Sorenti et  al. (2019); 3D: Le Cabec et al. (2015)). However, such analyses require an extremely specialized and expensive kit, whilst traditional morphometrics can be performed with callipers and a notebook, or GMM with photographs and a digitizing tablet. Thus, it is likely that morphometrics will continue to be part of the palaeontologist’s and archaeologist’s repertoire for some time to come.

Body size is arguably the most important ecological attribute of any mammal. It is connected to numerous intrinsic and extrinsic characteristics that are closely linked to survival and reproductive success. The former includes physiological processes such as thermoregulation and basal rate of metabolism, while the latter includes predator protection and dispersal ability (Damuth and MacFadden 1990). The body size of a mammal is also strongly linked to how it uses the landscape and how much of it is used. For example, in Borneo, the Asian elephant has a home range of up to approximately 600 000 000 m2, compared to 1400 m2 for the Rajah spiny rat on the same island (Nakagawa et al. 2007; Alfred et al. 2012). The loss of an individual tree in the Borneoan forest within the range of both species will be significantly more important to the rodent than the proboscidean. This illustrates the point that mammals of different body sizes use environments differently, and thus provide palaeoenvironmental information at potentially very different spatial scales. Amongst functional traits, the body size is probably the most plastic. An individual can experience changing body size over their lifetime in response to maturation, sex, season, and local and regional environmental conditions. An extreme example is demonstrated by Dehnel’s phenomenon, where in one study individual shrews were observed to decrease the size of their braincases in anticipation of winter by an average of 15.3% (Lázaro et  al.  2017). Significant body size changes can also be observed at the population level. For example, individuals at the leading edge of a biological invasion are often much larger than individuals at the core of the population  – the energy expenditure involved with expansion and the variable environmental conditions found at the edge of the species’ territory selecting for larger, better conditioned individuals (Chuang and Peterson 2016). Domestication will also significantly impact on body size (Tchernov and Horwitz 1991). However, most instances of body size changes examined by palaeoecologists will be observable on evolutionary timescales, involve intraspecific analyses, and invoke ecological ‘rules’ dictating directions of body size changes. The most widely known ecological theory on body size is known as Bergmann’s Rule (Clarke  2017, pp.  299–300). Essentially, it states that on average individuals of a mammalian species or group of closely related species will have larger body sizes in cooler climates and smaller individuals in warmer climates. Allen’s Rule is a corollary of this, ­predicting that protruding body parts will be shorter in cooler environments than in warmer ones (Mayr  1970).

­Locomotio 

These rules are based on the surface area to volume ratio, with larger bodies with smaller appendages having a smaller surface area relative to area, thereby minimizing heat loss. The relationship between body size and ­temperature can be used as a palaeoenvironmental tool (e.g.  Avery  2004). One other major rule has important implications for palaeoecology, and that is the Island Rule (Foster 1964). This describes the propensity of smaller animals to get very large and large animals to become dwarfed on islands. This has been observed on many islands with several well-­known examples (van der Geer et al. 2011) and is thought to be related to ecological release and resource limitations under insular conditions. Because ‘islands’ need not refer to bodies of land surrounded by water but can relate to any isolated environment, this ­pattern can be used to examine, for example, the historic fragmentation of landscapes by people (Schmidt and Jensen 2003).

­Functional Morphology This method examines structures in an organism and relates these to a specific biological function. In the case of zooarchaeological assemblages, these structures will be ones preserved on bones. This encompasses the size and shape of individual elements as well as areas of anatomical interest, such as muscle attachment areas that provide information on soft tissues, and points of articulation which provide data on range of motions. An organism’s structures are under evolutionary control and therefore optimize reproductive fitness in their environment. Thus, biological structures expressed by an organism are usually intimately related to the environments in which they are found (Plummer et al. 2008). Functional morphology can be used to infer environments qualitatively. This is the simplest method of analysis and only requires that the presence of a particular trait is closely related to a habitat type. For example, the number of thoracic, lumbar, and caudal vertebrae, among other variables, have been correlated with relative degrees of arboreality in tree shrews (Sargis 2001), and the craniodental morphology of ungulates has proven particularly fruitful for reconstructing diets (Janis and Thomason 1995) and thus the presence of grasslands or forests. More quantitative methods of functional morphology are commonly termed ecomorphology. These measure biological structures in order to quantify them in size and shape. Most commonly, this is achieved by measuring areas of interest with reference to anatomical landmarks and can be applied to two-­ or three-­dimensional

representations of skeletal elements or to skeletal elements themselves. Statistical ­techniques allow shape and size to be isolated and facilitate comparisons in an appropriate multivariate space. In all instances, a collection of specimens of known habitat preferences is necessary to provide the comparative framework in which to work. One advantage of many ecomorphological approaches is that species identities do not need to be established, provided the anatomical region of interest is preserved (Damuth et al. 1992). However, traits present because of a shared common ancestry have the potential to skew results and thus need to be considered prior to analysis (Scott and Barr 2014). Functional traits can also be compared at the community level, and the examination of the distribution of traits within communities is known as ecometrics. These types of analyses allow the study of ecosystem variability through time (Vermillion et  al.  2018). Ecometrics requires three variables – geographic ranges of species, an environmental factor of interest, and a measurable functional trait. Traits can include body size or be associated with dietary preferences or locomotor abilities and can reconstruct environmental gradients such as precipitation or temperature over local, regional, or continental spatial scales. For each community at a sampling site, an ecometric value – usually the mean – is calculated and compared to the environmental variable from that site (Vermillion et al. 2018). Significantly and strongly correlated links between traits and environments can be applied to fossil communities. Because ­ecometric means vary as a function of assemblage size, environmental inferences derived from these can be skewed, and care should be taken in controlling for taxonomic abundances and selecting appropriate environmental factors (Faith et al. 2019a).

­Locomotion Locomotion is important as a palaeoenvironmentally informative functional trait because it represents the physical interaction between a mammal and its environment. Successful locomotion does not just relate to movement through a landscape but encompasses activities affecting the evolutionary fitness of an organism including food acquisition, searching for a mate, fleeing predators, and avoiding inter and intraspecific competition. As such, there are strong phylogenetic controls on phenotypic traits that relate to locomotion. In active locomotion an animal propels itself through biomechanical actions such as leaping, running, or flapping. Passive locomotion, where an animal depends on the

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environment to move (e.g. rolling, sailing), is incredibly rare in mammals and is not considered here. Locomotion is a scalar trait as it can be geared towards travelling over large spatial and temporal scales (e.g. migration) or short sharp movements (e.g. predator avoidance). The parts of the skeleton most often involved in locomotion in mammals are the limbs and tails, and the functional demands of both long and short-­distance movements will be mainly preserved in the skeletal ­elements of these body parts. The primary types of environments that mammals move through are aquatic, terrestrial, arboreal, fossorial (subterranean), and aerial. Aquatic and aerial adaptations require the most specialized transformation of the typical mammalian body plan. In the most extreme examples, represented by whales, dolphins, and related marine mammals, there has been a complete loss of the rear limbs and significant restructuring of the forelimbs into flippers (Uhen  2007). Aerial adaptations are not as radical but nonetheless represent a significant change of forelimbs into wings that are easily discernible if preserved. Fossorial (i.e. burrowing) locomotion produces less extreme changes in the digits; however, it requires significant modifications to the ­forelimbs to optimize digging activities (Smith and Savage 1956). Determining terrestrial and arboreal locomotion will be of primary interest to archaeologists seeking to reconstruct palaeoenvironments. This is because the presence and nature of terrestrial versus arboreal mammals will provide strong indications on the abundance and distribution of trees on the landscape – an important environmental variable for humans and other hominins. While some mammals can be easily classified as terrestrial (e.g. bovid) versus arboreal (e.g. koala), many individuals spend at least some time locomoting through both sorts of environments. For instance, in the examples listed in the previous sentence, some goats are known to climb trees, and koalas are known to descend to the ground. Within terrestrial or arboreal environments, more precise classifications of locomotion can provide additional details on the types of environments present. Terrestrial locomotion in mammals can encompass walking, ­hopping, jumping, or running, with different types of locomotion more efficient or useful in different types of terrestrial environments, even for the same broad behaviour type. For example, some bovids rely on speed running to escape predators in open grassland. In closed forests, the ability to change directions quickly can be more advantageous. These different strategies are reflected in the foot bones of terrestrial mammals, making them useful indicators of heavy cover, light cover, wetland, forest, and open ­terrestrial environments (Louys et al. 2013; Plummer et al. 2015).

­Teeth and Diet Mammalian diets can be split into two broad groups: ­primary and secondary consumers. Primary consumers are those whose nutritional requirements are satisfied by ingesting plant matter, while secondary consumers subsist on non-­plant matter such as other animals. Primary consumers are often divided into three further major groups. Grazers are those animals that derive most of their food intake by consuming grasses. How much grass it takes for a species to be considered a grazer varies; however, more than about 70% monocots in a diet are commonly employed as a cut-­off (e.g. Gagnon and Chew 2000). Within grazers, further subdivisions can be made, for example, between variable grazers and obligate grazers. Browsers, on the other hand, can be defined as those species where dicotyledonous plants make up more than 70% of their diet (Gagnon and Chew 2000). Mixed feeders fall between those two categories. However, many different herbivorous feeding strategies are not encompassed within these broad classifications, such as frugivores, fungivores, and granivores. The focus on herbivores in the majority of palaeoenvironmental reconstructions using diet relies on the relationship between browsers and grazers and the relative abundance and distribution of trees on the landscape. However, palaeoecologists should beware of making conclusions simply based on the absence or presence of a grazer or a browser. For example, African grasslands are dominated by monocots, and thus we should expect grazers. However, they can also host dicots and fruits in sufficient abundance to support non-­grazing species such as the gerenuk Litocranius (Gagnon and Chew 2000). We often hear ‘you are what you eat’ in the case of tooth and bone chemistry. Tooth is more resistant to diagenesis than bone, meaning samples that are millions of years old will often preserve interpretable biochemical signals. For example, Harris et  al. (2020) successfully analyzed the teeth of North American Miocene equids and rhinocerotids dating between 23–15 Ma. However, bone tends to produce results for the last few tens of thousands of years, particularly for nitrogen isotopes which are only preserved in collagen. Tooth enamel from fossils can be measured for δ13C, which informs on past diets, as the photosynthetic pathways used by different plants preferentially discriminate between carbon isotopes, resulting in different 12C/13C ratios in their tissues. The most commonly used pathways, known as C3 and C4, relate largely to trees and tropical grasses, respectively. Thus, through analysis of carbon in fossil tooth enamel, animals can be defined in terms of proportions of C3 and C4 plants in their diets, which in turn informs on the habitats used by those animals. Meanwhile,

­Dental

δ18O in the same teeth can be used to examine the climate, although there is a complicated relationship between drinking water and precipitation in many regions. Bone also preserves δ13C, in addition to δ15N, which is used to examine the protein component in the diet. Such analyses now form a large field of study in both palaeontology and archaeology, and we refer you to Chapter 21 to learn more about these methodologies. Because omnivores and carnivores are less dependent on trees and grasses for nutrition, they are less likely to be used in palaeoenvironmental reconstructions. However, the use of stable isotope analysis in both omnivores and carnivores can reveal important insights into past ecosystems, such as differences in habitats occupied by carnivores versus herbivores, providing clues to the heterogeneity of the landscape at large spatial scales (e.g. Bocherens et  al.  1999). Most importantly, such studies allow the reconstruction of the trophic structure of a community of animals, the first step in reconstructing palaeofoodwebs (Fox-­Dobbs et al. 2008).

­Dental Wear The first contact between a mammal’s food intake and the mammal occurs in the mouth. Teeth begin the mechanical breakdown of ingesta, and the effects of this are reflected directly on the teeth in the form of wear. Dental wear occurs when the hardness and sharpness of an object in contact with a tooth are as great as, or greater than, the tooth. In general, the dental tissue in contact with ingesta is enamel; however, in some mammals such as xenarthrans (sloths, armadillos, and anteaters), adult teeth are composed entirely of dentine. Dental wear takes two forms: attritional and abrasive. The former refers to the formation of wear facets through contact between teeth (tooth-­on-­tooth contact), while the latter occurs through contact with ingesta (tooth-­on-­food contact). While most ingesta are considerably softer than enamel, both adhering grit and phytoliths – mineralized particles formed inside plant tissue  – are suggested as contributing to wear (Lucas et al. 2014). The first effects of wear on a mammal’s teeth take the form of individual pits and scratches on the surface of the tooth. The study of these is known as microwear. Because of the different hardness properties of leaves and grasses and the different biomechanical adaptations herbivores have evolved to chew those plants, the distribution and proportion of pits and scratches vary according to whether a mammal is ­predominately a grazer, a browser, or a mixed feeder. Modern analyses of microwear commonly involve the calculation of textural variables that represent ways of quantifying

Wea 

patterns of surficial damage and comparing these to species of known diets (Scott et al. 2005). This method is predominately used to reconstruct diets amongst herbivores, but microwear can also be informative in examining carnivore diets (DeSantis and Patterson 2017). Because the microwear signal is subject to overprinting by the next mouthful of food, it usually represents the ‘last meal’ of the mammal being examined, and thus may not be representative of that individual’s lifetime diet (Teaford and Oyen 1989). The cumulative dental wear an animal experiences over its lifetime is informative for palaeodietary reconstructions and is known as mesowear. At its simplest, mesowear examines the relative effects of attritional versus abrasive wear on the gross morphology of the tooth (Fortelius and Solounias  2000). Attritional wear results more often in mammals that chew softer foods such as browse and produces sharper cusps and deeper valleys between cusps. Abrasive wear, on the other hand, is mostly found in mammals that process large amounts of tough particles associated with a grazing diet. This type of wear produces rounded to flattened cusps, resulting in shallow to non-­ existent valleys between cusps. For each species, the proportion of sharp, high cusps versus rounded, low cusps is calculated and compared with mammals of known diets. This method requires the identification of dental remains to tooth position and species, a comparative set of ‘typical’ modern herbivores, and a minimum number of individuals per species for the mesowear signal to ‘stabilize’ (Fortelius and Solounias 2000; Louys et al. 2009). Mammals respond to dental wear constraints over an evolutionary timescale, and this response can also be observed in teeth. The hypsodonty index refers to the height of the tooth crown relative to its width, with species demonstrating high indices associated with grazing lifestyles (Janis 1988). In extreme grazing forms, such as wombats, the teeth become ever-­growing and rootless. Thus, the shape of the tooth itself provides a good indication of the evolutionary history of diet in that species. However, this evolutionary history may not necessarily be indicative of present-­day diets. For example, goats, takins, and gorals are all hypsodont but predominately browsers. Because of the different scales at which each dental wear variable measures palaeodiet, a combination of all three techniques, where possible, provides the most holistic reconstruction of vegetation (Strani et al. 2018).

Case Study – Ti’s al Ghadah The Pleistocene site of Ti’s al Ghadah, in the Nefud Desert of Saudi Arabia, represents at least three faunal depositional events in an interdunal depression (Stewart et  al.

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Figure 11.3  Ti’s al Ghadah Unit 5 sands, from which the majority of fossils were extracted. Massive marls indicative of freshwater lakes can be observed sitting on top of the sand unit. The environments present during the deposition of the Unit 5 sands are reconstructed as productive grasslands reminiscent of East African savannahs, very different from the hyper-­arid conditions found in the Nefud Desert today. Source: Photo credit: Julien Louys.

(2019); see Figure  11.3). The site has been the subject of considerable study since the first fossils were reported. The site was one of three described by Thomas et  al. (1998), who, based on the presence of savannah-­adapted taxa, suggested they represented open lacustrine grasslands. This interpretation was further bolstered by stable isotope analyses of two fossil teeth from Ti’s al Ghadah – one elephant and one alcelaphine  – that revealed that these two individuals were consuming a C4-­dominated diet. This environment contrasts markedly with the hyper-­arid desert environment found at the site today and suggested that the Arabian Peninsula was once much wetter and more productive than it is now. Systematic excavations at Ti’s al Ghadah were reported by Stimpson et al. (2015, 2016). They focused their efforts on one stratigraphic layer at the site, ‘Unit 5’, which produced dates between c. 500–300 ka. In addition to the faunas previously recovered by Thomas et  al. (1998), these investigators recognized two species of large-­bodied mammalian carnivore, from which they deduced that the western Nefud sustained a significant Middle Pleistocene biomass. Stimpson et  al. (2016) also applied mesowear analysis to elephant remains from the site. The method used was a version modified by Saarinen et al. (2015) for proboscideans and is based on angle measurements from worn dentin valleys of elephant teeth. The two fossil teeth from Unit 5 analyzed in this way produced angles of wear

that indicated a grass-­dominated mixed feeder and a grazer, respectively. Thus, a multidisciplinary combination of methods applied to the mammal fossils found at the site consistently pointed to extensive grasslands. These environmental conditions proved highly attractive to Middle Pleistocene hominins, and Roberts et al. (2018) and Stewart et  al. (2019) reported on hominin-­modified bones from Unit 5. Roberts et al. (2018) also expanded on the two isotope records in order to provide a more extensive analysis of palaeoenvironments present. They examined both carbon and oxygen isotopes, and for oryx sampled sequentially along the growth axis of the tooth. This type of analysis has the potential to reveal seasonality signals, as the teeth of the taxa sampled grow over a period of more than a year. They showed that all the sampled species (elephants, oryx, hartebeest, equids, and bovids) had diets dominated by C4 vegetation. Samples for oxygen isotope analyses were divided between obligate and non-­obligate drinkers, and the results demonstrated that the relationship between these two groups was not different from humid East African savannah environments, but that they differed significantly from those in the modern Nefud Desert. Thus, the environmental conditions at the site were considerably wetter during the Middle Pleistocene and support the geological evidence indicating permanent water bodies were present (Stewart et  al.  2019). Finally, serial sampling of oryx teeth demonstrated that access to

­Habitat 

vegetation was independent of seasonality and that, therefore, a homogenous and constant source of vegetation was available to herbivores. The combination of palaeoenvironmental reconstructions from the mammals, alongside the sedimentological record and taphonomic analyses all suggest that Unit 5 at Ti’s al Ghadah represented a serial predation hotspot in a homogenous and lush lakeside grassland (Stewart et  al.  2019). Such environments would have been highly attractive to hominins on their extensive dispersals out of Africa (Groucutt et al. 2018).

­Palaeoclimate Identifying palaeoclimate from mammalian remains is similar to identifying habitats, in that much of it relies on comparison with modern analogues. Small mammals are particularly useful when identifying climate, as they are likely to be much more responsive to changes in temperature. However, large mammals also have their place, particularly when looking at the Northern hemisphere in the Pleistocene, where certain species evolved to survive in both the glacial and interglacial periods. The adaptations to the cold periods included the development of a long hairy coat for mammoths and woolly rhinos, and the reduction in the size of ears and other extremities to reduce heat loss (Lister and Bahn 2007). The animals adapted to the warmer periods tended to be larger (e.g. the straight-­tusked ­elephant Palaeoloxodon antiquus was ~0.6 m taller at the shoulder than its woolly mammoth cousin) and were mixed feeders or browsers, e.g. the rhinoceroses of the genus Stephanorhinus (van Asperen and Kahlke  2015). Thus, the finding of specific species may indicate the relative temperature and habitat at the time, which may be examined further using stable isotopes. Analysis of δ18O in woolly mammoth enamel indicated a mean annual temperature 9–10 °C lower than today during the Younger Dryas in Estonia (Arppe and Karhu 2010), while the presence of the European pond turtle (Emys orbicularis) in England during the Holocene suggests a mean annual temperature 2–2.5 °C higher than today (Sommer et al. 2007). Yalden (2001) gives an excellent overview of climate and mammals in his chapter in the previous edition of this book.

­Habitats The habitat of an animal is fundamentally entwined in how it lives, its competitors, and its social systems. For example, large open-­country mammals tend to be cursorial (adapted for rapid locomotion) and group-­living. Both are

adaptations to having little vegetation cover, with speed being used to either capture prey (cheetahs) or evade predators (zebras, pronghorns), and social groups allowing greater vigilance to identify threats (some individuals can be on guard, while others search for food), or in the case of predators, they can work in groups to obtain prey, which then helps when defending kills from theft by other taxa (kleptoparasitism). Mammalian fossils can be used to identify palaeohabitats in a variety of ways, but particular issues arise when there are no modern analogues to the extinct animals, as is the case with the various sabre-­toothed cat genera from the Pliocene and Pleistocene (e.g. Dinofelis, Megantereon, Homotherium, Smilodon). Here, careful study of the anatomy of these taxa has been required to try to determine exactly how they could have used their enlarged canines to capture and kill their prey animals. In the case of Dinofelis and Megantereon, it is likely that they were solitary ambush hunters in bushy habitats (Turner and Antón  1997), while it has been suggested that Homotherium was an open country social hunter (Antón  2013, p.  185). Analysis of body mass data for Pleistocene and extant carnivores, and the contents of fossil carnivore dens suggests that young megaherbivores (such as elephants, rhinos, and ground sloths) are likely to have formed a considerable part of large carnivore diets (Van Valkenburgh et al. 2016). The direct linkage between habitat types and taxa allows an initial reconstruction of habitats around a given site, but this pre-­supposes that the taxa found there is a genuine reflection of the local area and not a result of taphonomic bias. For example, palaeoenvironmental reconstructions of African hominin sites often identify the local habitat as mosaic (grass, trees, water) (Reynolds et al. 2015), but to what extent does this reflect the local habitat or simply a merging of the local signal either spatially (i.e. the site has accumulated taxa from multiple habitats that may not have lived together), or temporally (that the vegetation has changed, say over a glacial-­interglacial cycle but the temporal resolution of the site makes it appear that these animals were all present at the same time)? A study of modern African savannahs using remote sensing found that single landcover classes were present at only six out of 4628 sites studied, indicating that mosaic habitats were almost ubiquitous (Marston et al. 2019), and a similar result was found when the analysis was conducted at a variety of different scales (O’Regan et al. 2016). In contrast, non-­analogue environments also exist  – where the habitats that we identify in the past appear to have no representation in the present (e.g. Faith et al. 2019b), and there is considerable discussion over the role of ‘cryptic refugia’ in northern Europe, where temperate animals such as red squirrel (Sciurus vulgaris) appear to have survived in areas that were previously considered to

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be too cold (Stewart and Lister  2001). More recently, the cryptic/southern dichotomy has been scrutinized through the analysis of small mammal DNA, which has indicated that each species may have had its own survival and recolonization trajectory (Pedreschi et al. 2019).

­Communities Issues arising from differences in ecological preferences between modern and past mammals (i.e. a lack of ecological uniformitarianism) will be most impactful when considering only one or a few taxa in any environmental reconstruction. One means of increasing the accuracy of these reconstructions is to examine the whole community represented in an assemblage. In much the same way that habitat preferences of an individual species can be used to indicate the presence of this habitat in the past, the environmental preferences of a mammal community can be used to reconstruct such environments (Andrews et al. 1979). In archaeological deposits, a faunal community can be defined as all the species found together at one time and in one place. Usually, this means all species found in one stratigraphic layer within the spatial bounds of a site are considered a community, even if direct interactions between individuals cannot be demonstrated. Thus, there is some measure of spatial and temporal averaging present in any definition of a palaeocommunity that can introduce noise in environmental reconstructions. These can’t be removed, but they can be specified, controlled, and bounded such that they don’t invalidate reconstructions (Behrensmeyer and Reed 2013). In order to facilitate comparisons between modern and fossil systems, species in a community are grouped according to common attributes. Two primary types of groupings are used: taxonomic and ‘taxon-­free’. The first groups taxa at taxonomic levels above species, while the other groups them based on shared functional traits. The use of groupings has the added benefits of allowing the inclusion of taxa that are identifiable to different taxonomic scales as well as the inclusion of extinct taxa not found in the modern comparative communities. Comparisons between modern and fossil communities are made in multivariate space using proportion data – that is, the proportion of taxa falling within each group. Common multivariate analyses include principal components analysis and discriminant functions analysis. Because of this, each community must have a minimum number of species and groups to satisfy the statistical technique used and allow enough discriminating power to tell different habitats apart. Generally, the more ecologically complex the habitats being compared, the more species are needed to confidently tell them apart, and care should be

taken to select the most appropriate modern comparative communities (Louys et  al.  2009). Likewise, when using functional groupings, ecological traits should be chosen that are suitable for the assemblage(s) under consideration. Including small modern mammals where archaeological and fossil deposits are lacking in those species, for example, could unnecessarily skew results (Louys and Meijaard 2010). For this reason, flying mammals are usually also excluded from such analyses. Finally, it should be noted that communities further back in time may not have any modern analogues, such that they fall outside of the multivariate space defined by modern communities (Faith et al. 2019b). This is not necessarily fatal to these types of analyses, as such palaeocommunities may still be reasonably classified to a habitat type. However, while habitats may be similar, the functioning of ecosystems would likely have been quite different.

­Summary and Thoughts for the Future While mammals may not provide the level of precision and specificity of ecological information as other proxies, they are nonetheless extremely valuable to archaeologists seeking to understand past environments for two principal reasons. Firstly, mammals are easily recognizable and ubiquitous in many archaeological assemblages. Thus, they are almost always collected in excavations and surveys. This is particularly true for large-­bodied mammals, but it has also become standard practice to collect microfauna through sieving or otherwise. Secondly, mammalian remains recovered from archaeological deposits can be subjected to a wide variety of environmental reconstruction techniques, as we have hopefully demonstrated in this chapter. This means that almost any bones or teeth have environmental stories to tell. Moreover, the application of different techniques on the same remains has the potential to inform on past environments at different spatial, temporal, and evolutionary scales. The use of appropriate palaeoecological methodologies and techniques on mammal remains can yield substantial amounts of information on how past ecosystems operated and functioned, and thus by inference how humans fit in these. Further development in emerging technologies will no doubt lead to refinements in existing techniques as well as the development of new ones. Mammal remains, and in particular, their bones and teeth, still hold untapped potential for ecological insights. We expect that advances in 3D and tomographic scanning technologies will increase the levels of information discernible in physical structures, while the increasing refinement in genetic and proteomics will yield older and more specific insights into the identity

 ­Reference

and relationships of ancient mammals. The application of old technologies to explore new ecological avenues also holds considerable promise, for example the use of traditional histological analysis to examine skeletal responses to environmental conditions (Miszkiewicz et  al.  2020). However, the core principles of zooarchaeology and

palaeontology will always remain the cornerstone of any environmental reconstruction. The physical examination of bones and teeth with the naked eye and under the microscope and comparisons with appropriate modern skeletal collections remain critical skills for any practitioner of these methods.

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12 Lake and Peat Records of Climate Change and Archaeology P.G. Langdon1, A.G. Brown1, C.L. Clarke1, M.E. Edwards1, P.D.M. Hughes1, R. Mayfield1, A. Monteath1, D. Sear 1, and H. Mackay 2 1 2

Palaeoecology Laboratory (PLUS), School of Geography and Environmental Science, University of Southampton, Southampton, UK Department of Geography, Durham University, Durham, UK

Lake and peat sediments are frequently used to reconstruct palaeoclimate records from all continents using a variety of proxy techniques. The use of these sediments for reconstructing climate change has historically (before the last 20 years) focused on the analyses of fossils (plants and/or animals) that showed clear affinities with different climate regimes through an understanding of modern analogues of various individual taxa and assemblages. More recently, and certainly within the last 20 years, alternative techniques have been developed based mainly around advanced geochemical and molecular analyses of lake and peat sediments that can act as independent proxies for reconstructing past climate change and human impact. These new techniques, coupled with statistical advances in analyzing fossil datasets, have led to major syntheses of regional ­climate change from sedimentary archives (e.g. Kaufman et  al.  2020). In regions where peats and lake sediments are prominent, these records can be used as backgrounds/ drivers against which to assess archaeological contexts/ change. This chapter explores the advances that have occurred in the last 20 or more years for using lake and peat sediments to reconstruct past climate change. It then goes on to demonstrate the impact these advances have had for palaeoclimate research, and implications for archaeology.

­Lake Sediment Records Lakes are excellent sources of sediment from both autochthonous (within-­lake biological production and chemical precipitation) and allochthonous (material originating from the hydrologic catchment and beyond) inputs, which have accumulated over time. Lakes and peat records occur

on all continents and have been used to reconstruct ­climate, environments, and vegetation from Svalbard in the Arctic (Alsos et al. 2016) to Antarctica (Lyons et al. 2006). The continuous accumulation of sediment means that ­fossil remains (e.g. pollen, spores, plant macrofossils, insect remains, diatoms, and charcoal), geochemical data (e.g. XRF, stable isotopes), and molecular components (e.g. ancient DNA and lipid biomarkers) are preserved in robust stratigraphic contexts, enabling the establishment of well-­ defined records, although chronological problems can still arise. Sediment records derived from lakes situated within or adjacent to archaeological sites can provide valuable information about the regional and local landscapes that were the focal points of past human activities.

Fossilized Invertebrate Remains as an Indicator of Past Temperature Fossilized insect remains are often abundant in a wide range of sediments, including lake, river, and peat deposits. A wide variety of invertebrate orders can be found preserved in sedimentological archives and used to interpret past environmental conditions. These include beetles (Coleoptera), the larval remains of many two-­winged flies (Diptera), notably non-­biting midges (Chironomidae), as well as other groups such as water fleas (Cladocera), caddis flies (Trichoptera) and very occasionally caddis fly larval tubes. As a separate chapter exists on ‘Insects as palaeo­ environmental and archaeological indicators’ (Chapter 10), here we only provide a brief overview regarding their use in lake and peat contexts. Each invertebrate group can provide valuable environmental information (e.g. air temperature, water temperature,

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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water quality, etc.); however, preservation of identifiable parts to a useful taxonomic level is a significant control over the usefulness of these organisms. Coleoptera and Chironomidae are two of the best-­preserved invertebrates that are used for climate change reconstructions. Hard chitinous materials, which form parts of the invertebrate exoskeletons, preserve well and can enable the remains to be identified to species or genus level. A large number of beetle species show clearly defined thermal tolerances, and to create Coleoptera palaeoclimatic reconstructions, the mutual climatic range (MCR) technique was devised by Atkinson et al. (1987). This enables the distribution of beetle species to reflect climatic conditions, for example summer temperatures or the degree of seasonality (annual temperature range) (Atkinson et al. 1987; Elias 2007). MCR modelling can now be done through the BugsCEP database and software, which also has ecological information (Buckland and Buckland 2006). Coleoptera have long been used as indicators of past climate across late Quaternary and Lateglacial timescales (e.g. Ashworth 1997; Atkinson et  al.  1987) as well as more direct indicators of human occupation and impact (e.g. Robinson 2001). However, a remaining disadvantage of Coleoptera reconstructions is the rarity in which the remains are found in sediments (Lemdahl 2000), resulting in low temporal resolution and large quantities of sediment (often >2 l) required to obtain adequate numbers of fossil beetle remains (Elias and Matthews 2014). These large samples of sediment are often deposited over long periods of time – up to decades; therefore, the inferred temperatures often produce large estimate ranges, meaning that beetle records commonly lack the precision and accuracy to record short-­term or rapid climate changes (Walker  2001). Consequently, Coleoptera reconstructions often hold better weight as ‘snapshots’ in time than continual palaeoclimate records, as in Aalbersberg and Litt (1998). This is not so much a problem archaeologically as sites often comprise a series of short-­lived contexts, which are also snap-­shots in time and space. Chironomids are non-­biting midges in the family Diptera (Brooks et al. 2007). The larvae reside in the sediments of freshwater bodies such as ponds, lakes and rivers. They are a commonly used climatic indicator as they have narrow ecological optima, they exist in a large range of aquatic biotopes, and they are extremely abundant. They show particularly high diversity in temperate regions (Brooks et  al.  2007). There are a large number of advantages to using chironomids as a proxy for past environmental change. Chironomid larval head capsules are highly identifiable as they are well preserved in sediments, especially late-­Quaternary deposits. They are identifiable to genus level and occasionally to species level. Chironomid

assemblages are species-­rich, with many taxa sharing similar habitats, and their communities respond rapidly to environmental changes (Brooks and Birks 2001). The head capsules are small in size (c. 50–1000 μm), and, depending on the origin of the sediment, a sample size of c. 0.5–6 cm3 is typically required for analysis. Sometimes, in archaeological contexts, the range of species can be restricted or biased by unusual conditions, for example where anthropogenic impacts are superimposed on changes associated with a naturally complex and dynamic physical environment, and in these contexts, intra-­specific environment-­ driven mutations can be recognized (Ruiz et  al.  2006). A large advantage of chironomid reconstructions is not only their environmental sensitivity but also the high temporal resolution that can be achieved and that can be aligned with other key indicators in multiproxy studies. An archaeological example of this is research on crannogs (relatively small human-­created islands in lakes or sea loughs) which has used chironomids alongside cladocera, diatoms, ­pollen and, most recently, molecular methods (O’Brien et al. 2005; Brown et al. 2021). Their use as a temperature indicator has resulted in the production of quantitative estimates of past temperature changes in continental locations, notably across much of the northern hemisphere (e.g. Self et  al.  2011; Fortin et  al.  2015; Heiri et  al.  2015; Zhang et  al.  2017), often with links to archaeological ­contexts (e.g. Taylor et al. 2017; Blockley et al. 2018; Wooller et al. 2018).

Geochemical and Molecular Records of Climate Change Derived from Lake Sediments Geochemical Indicators as Climate Proxies

There is a long history, well over 50 years, of geochemical analyses on lake sediments to reconstruct past environmental change, with reconstructions often focusing on catchment changes that may (or may not) be a result of climate change. Perhaps the most important change within the last 20 or more years has been the increased resolution of geochemical analyses, especially through X-­ray fluorescence (XRF) scanning techniques such as 1-­D ITRAX core scanning (Croudace et  al.  2019), 2-­D elemental mapping for ultra-­high resolution analysis of core geochemistry (Croudace et  al.  2019), and CT-­Scanning at sub-­annual resolution that can quantitatively provide 3-­D stratigraphy of cores based on density differences (e.g. St-­Onge and Long 2009). The maximum resolution of ITRAX scanners varies from 500 to 200 μm, with scanning times for 1-m cores typically taking a few hours (Croudace et al. 2019). 2-­D elemental mapping systems can scan areas of c. 20 cm2 in a few hours, providing information on microstratigraphic geochemistry, which is helpful in the interpretation

­Lake Sediment Record 

of laminated sediments (Croudace et al. 2019). Weltje and Tjallingii (2008) recommend the careful application of log-­ ratios of elemental intensities from ITRAX core scans combined with statistical analysis to account for variations in core water content, organic matter and to express in mass equivalents to bulk XRF. Combined with detailed elemental mapping and microscopic observations of sediment textures, post-­processing of these data can lead to more refined interpretations, for example at seasonal scales, in the reconstruction of depositional environments and associated drivers (Fielding et al. 2020). Micro-­XRF analyses are now widely used on lake sediment sequences. Element ratios can be used to identify inputs of, for example, clastic elements that may relate to climate-­driven catchment processes (e.g. Gosling et al. 2020). Often calcium/titanium (Ca/Ti) ratios are used as proxies of effective moisture, as calcium precipitation will be enhanced during evaporative concentration of lake waters, whereas titanium is an unambiguous indicator of allochthonous inputs. Hence an increase in Ca/Ti ratios will relate to drier climate. Other elemental ratios can be used to infer grain size (e.g. Zr/Rb). Rb is typically associated with clay fractions, while Zr is often enriched in coarse silts. Other XRF measurements can also act as proxies for  climate-­induced change, such as the ratio between ­incoherent/coherent scatter (inc/coh) that has been shown to be a proxy for organic matter (Chagué-­Goff et al. 2016), although it can be limited by saturation of the signal and so is typically not a complete replacement for loss-­on-­ignition (LOI). These element ratios from scanning XRF are now used in many palaeoenvironmental studies. For example, Lamb et  al. (2018) show how element ratios from a lake sediment record from Lake Tana, Ethiopia, can be used to reconstruct past abrupt climate change. They compared this reconstruction over the last 150 000 years with the archaeology from early modern human fossil sites to argue that the last interglacial climate was relatively stable and moist; conditions that would support models of early, multiple dispersals of modern humans from Africa. Geochemical records from tropical lake sediment sequences have been used to reconstruct both disturbance events associated with, and thus the timing of, human arrival on the Pacific Islands and the changing climate over the Holocene (Gosling et al. 2020; Sear et al. 2020). More details are provided below, but here we focus on how the geochemical analyses were used. On the southern Cook Island of Atiu, ITRAX core scans of 8 m of laminated lake sediments showed an increase in titanium (Ti/inc). In this record, titanium is indicative of terrigenous material washed into the lake during rainfall; however, the titanium abundance is also influenced by the availability of titanium-­ rich soils. Figure  12.1 illustrates how the (Ti/inc) ratio

rapidly increases with the arrival of humans on Atiu, which is interpreted as resulting from the burning and clearance of vegetation and exposure of catchment soils to erosion (Sear et al. 2020). In Lake Emoatul, Vanuatu, Ti/inc μXRF ITRAX data record changes in hydroclimate that correspond with an independent precipitation proxy derived from algal lipid biomarkers (Maloney et  al.  2019) and with instrumental precipitation measurements at the top of the lake sediment archive. In Mexico, Metcalfe et al. (2010) use similar geochemical proxies to reconstruct variations in hydroclimate that correspond with phases of drought and societal changes in the Maya civilization. Stable Isotopes of Carbonates and Aquatic Invertebrates

Since the pioneering work of McCrea (1950) and Urey et al. (1951), stable isotope geochemistry has been widely applied to a range of marine, terrestrial and lacustrine settings as a means for reconstructing past temperature (e.g. Leng and Marshall  2004; Wooller et  al.  2004; Langdon et al. 2010; Heiri et al. 2012; van Hardenbroek et al. 2018). In lacustrine environments, the technique has been applied to both bulk sediment (namely δ18O in carbonates and biogenic silica) and fossilized remains preserved within them (commonly δ18O in chitin of invertebrate remains). From these analyses, an annual or seasonally-­specific climate signal can be gained, depending on the material used for stable isotope analysis. In hydrologically open lakes which have a degree of through-­flow, oxygen isotope ratios in the water (δ18Olakewater) predominantly reflect the isotopic composition of precipitation (δ18Oprecipitation) received by the lake via rainfall, streams, and groundwater; thereby, indirectly, they record a climate signal (Clark and Fritz  1997; Leng and Marshall  2004; Leng and Henderson  2013). In such systems, δ18O values in the lake water and sediment show only small variations, which are typically ascribed to variations in the δ18Oprecipitation and thus the air temperature at which condensation took place (Gat  1996; Wooller et  al.  2004; Finkenbinder et  al.  2016). In contrast, large, hydrologically closed lake systems, particularly those in arid regions, predominantly lose water via evaporation, resulting in variable and elevated δ18O values in the lake water and sediments. Isotope records from the sediments of closed lakes often show large fluctuations in composition due to changes in the ratio of the amount of precipitation to evaporation as climate changes (e.g. Barker et al. 2001; Jones and Roberts 2008; Gibson et al. 2016; Hua et al. 2019). The size of the lake in relation to its catchment, the residence time of the lake water, and processes affecting the

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Figure 12.1  Examples of the use of ITRAX uXRF core scanning to reconstruct (a) the increase in soil erosion (Ti/inc) as a result of landscape disturbance by the arrival of the first humans on the island of Atiu, S. Cook Islands. Source: Adapted from Sear et al. (2020). (b) Reconstructing hydroclimate using (Ti/inc) terrigenous inwash proxy data and measured rainfall data. All data is detrended and normalized by z-­scores. (c) Use of (Ti/inc) terrigenous in wash proxy to reconstruct long-­term variability in precipitation in Lake Emoatul, Efate, Vanuatu. ITRAX data shown again an independent rainfall proxy based on hydrogen isotope ratios of algal lipids. Source: Adapted from Maloney et al. (2019).

­Lake Sediment Record 

water balance are important controls on the strength of the relationship between δ18Olakewater and δ18Oprecipitation. Net evaporation will result in preferential removal of the lighter 16 O isotope and more enriched δ18Olakewater values (Mayr et al. 2007). It is, therefore, crucial to understand the basic hydrology, for example open vs closed system and associated controls, of a lake that is to be used for palaeoclimate reconstruction and the local processes that might control and modify its δ18O signal. Several disequilibrium processes (e.g. species-­specific vital effects and micro-­environment induced changes) could confound the relationship between the isotopic composition of the mineral or fossil remains and the prevailing climatic conditions (e.g. Coletta et al. 2001; Mayr et al. 2015). The effect of these disequilibrium processes should be quantified, and robust calibration studies using modern analogues are necessary to establish the precise systematics between the measured δ18O signal, the δ18O of the ambient lake water, and climate. A variety of different authigenic (e.g. lacustrine carbonates) and biogenic (e.g. diatom silica, chitin from aquatic invertebrates and crustaceans) materials have been used in stable isotope analysis as a means for reconstructing past temperature. In lacustrine environments, the δ18O of ­carbonate is primarily a function of the δ18Olakewater from which the carbonate was precipitated and the temperature at which the carbonate was precipitated (Eicher and Siegenthaler 1976; Leng and Marshall 2004). In most temperate and high-­latitude regions, authigenic lacustrine ­carbonates are precipitated mainly during the summer months, when phytoplankton productivity is high (Leng et  al.  1999). In the tropics, phytoplankton growth may occur throughout the year, and authigenic carbonate precipitation is commonly related to annual lake-­water mixing and nutrient availability (Lamb et al. 2002). Stratigraphic changes in the δ18O of lacustrine carbonates are largely considered to reflect changes in summer or mean annual temperature, depending on the location, the timing of carbonate precipitation, and the isotope mass balance of the lake under investigation. The advantage of using authigenic lacustrine carbonates for reconstructing palaeoclimate compared to other biogenic materials (including biogenic calcite from mollusc or ostracod shells) is that it provides an integrated climate signal for the bulk sediment sample, which may span tens to even a hundred years depending on the sedimentation rate (Leng and Marshall  2004). Furthermore, the use of bulk sediment means that it is possible to bypass the laborious step of identifying and picking out the biogenic material required for analysis. However, it can be difficult to distinguish authigenic carbonates from allogenic components derived from the terrestrial environment, creating a risk of contamination of the isotope signal from a washed-­in component.

Aquatic invertebrates such as chironomids and cladocera spend a considerable proportion of their life cycle submerged within a surface water body, particularly during the larval stage. The δ18O of their chitinous exoskeleton has been shown to reflect the δ18O of the ambient lake water at the time of cuticle formation, which is normally during the summer months (Wooller et  al.  2004; Verbruggen et  al.  2011). In lacustrine environments, stratigraphic changes in fossil invertebrate δ18O values can be used to infer changes in δ18Olakewater and, indirectly, past climate and environmental conditions (van Hardenbroek et al. 2018). Highly sclerotized chitinous remains of aquatic invertebrates are generally abundant and well-­preserved within lake sediments, and no temperature-­dependent fractionation processes are expected to occur during the synthesis of their chitin (Miller  1991; Stankiewicz  1997; reviewed in van Hardenbroek et al. (2018)). The ability to identify these remains under a microscope minimizes the possibility of problems related to terrestrial contamination faced by records derived from authigenic carbonates and aquatic cellulose, for example. Stable isotope ratios in authigenic and biogenic materials have quickly become a routine palaeoenvironmental proxy in Quaternary science over the past 20 years. Although the operating procedures used remain largely unchanged, the nature of the material used to generate palaeoclimate records has diversified over time, with technical advances facilitating the analysis of ever-­decreasing sample sizes. Several studies have now applied these techniques to key archaeological sites with an aim to provide a palaeoenvironmental context for emerging archaeological finds (e.g. Candy et al. 2006, 2011; Wooller et al. 2012). These records have provided important insights into the prevailing climate conditions at the time of human occupation and/or changing human practices. Lipid Biomarkers and Compound-­Specific Isotopes

Analytical advances over the past two decades have facilitated major developments in understanding and applying organic geochemical molecular climate proxies (termed lipid biomarkers) to lake and peat deposits. These source-­ specific molecular fossils are produced by organisms such as bacteria, archaea, fungi, plants, and animals (Peters et al. 2005). They are preserved in situ and are stable over geological timescales (Killops and Killops  2005; Peters et al. 2005). A wide variety of lipid biomarker compound classes have been used to reconstruct past environmental change from wetland sediments, such as alkyl lipids (n-­alkanes, n-­fatty acids, n-­alcohols, unsaturated fatty acids, hydroxy acids, and alkenones), glycerol dialkyl ­glycerol tetraethers (GDGTs), isoprenoids, steroids and cellulose (e.g. Killops and Killops  2005; Peters et  al.  2005;

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Eglinton and Eglinton 2008; Castañeda and Schouten 2011; Holtvoeth et al. 2019). Lipid biomarkers are extracted from sediments using techniques such as microwave-­assisted extraction, accelerated solvent extraction, and ultrasonication. Individual compound classes are then isolated from the total lipid extract, and individual compounds are identified using gas chromatography-­mass spectrometry (GC-­MS). A key advantage of incorporating lipid biomarker analysis within multiproxy palaeoclimate studies is the ability to characterize several classes of lipid compounds from the same total lipid extract, which can provide diverse insights into climate systems, both directly (e.g. by reconstructing precipitation and temperature) and indirectly (e.g. by reconstructing vegetation and therefore moisture regimes) (Castañeda and Schouten 2011). Common target compounds within lacustrine and peat-­based lipid biomarker palaeoclimate studies include n-­alkanes, alkenones, and GDGTs. Reconstructions of vegetation and climate change can be obtained using straight-­chain hydrocarbons, such as n-­alkanes, n-­alcohols, and n-­alkanoic acids, which originate from plant waxes. The chain lengths of these compounds (i.e. number of carbon atoms) indicate their biosynthetic origin: for example, higher land plants produce long chain n-­alkanes to protect against water loss, leaching of minerals, bacteria, and fungi (Meyers and Ishiwatari  1993; Bianchi and Canuel  2011), whilst algae and aquatic plants produce short chain n-­alkanes (e.g. Cranwell  1973; Nichols et  al.  2006). The identification of average n-­alkane chain lengths (Gagosian and Peltzer 1986; Poynter et  al.  1989; Schefuss et  al.  2003) and diagnostic ratios of n-­alkane compounds (e.g. Ficken et al. 2000; Nott et al. 2000; Nichols et al. 2006; McClymont et al. 2008) can therefore be used to reconstruct changes in vegetation, temperature, and humidity. Palaeohydrological leaf-­wax reconstructions have been validated through comparisons with other well-­established proxies, such as reconstructions of peatland water-­table depth based on testate amoebae (e.g. Nichols et  al.  2006); they are particularly useful when microscopic remains are poorly preserved (Nott et al. 2000; Pancost et al. 2002). Considerations when interpreting leaf wax reconstructions include compound transport mechanisms (Pancost and Boot 2004), differences in lipid production rates among plant taxa (e.g. Pancost et al. 2002), and the taxonomic resolution of plant identifications (e.g. Nichols et al. 2006). Leaf-­wax lipids (n-­alkanes, n-­alcohols, and n-­alkanoic acids) are common targets for one of the most powerful lipid biomarker palaeoclimate tools: compound-­specific isotope analysis (CSIA; Holtvoeth et  al. (2019)). Stable hydrogen and carbon isotope analyses are commonly applied within wetland palaeoclimate studies. They have

been used successfully in diverse locations from the Arctic to the tropics to reconstruct changes in vegetation (e.g. Sinninghe Damsté et al. 2011) and palaeohydrologic conditions (e.g. Sachse et  al.  2012; McFarlin et  al.  2019). Interpreting CSIA records can be complex since many different processes influence isotopic values (Castañeda and Schouten 2011; Holtvoeth et al. 2019). However, CSIA palaeoenvironmental records have made important positive contributions to several archaeological debates, such as the role of drought in the Terminal Classic decline of Maya civilization (Douglas et al. 2015) and the influence of climate on hominin migration patterns in North Africa over the last 200 ka (Castañeda et al. 2009). Temperature reconstructions from lake sediments can be generated using lipid compounds termed long chain alkenones (LCA), which are aliphatic unsaturated ketones produced by haptophyte algae. LCA were originally used as sea-­surface palaeothermometers (Brassell et  al.  1986); however, their utility in reconstructing temperature in freshwater lakes has been demonstrated and developed over the past two decades (e.g. Zink et al. 2001; Castañeda and Schouten 2011). The proportions of LCA compounds produced depend on temperature, and therefore, reconstructions can be derived from the relative abundance of organic compounds (LCAs), for example indices such as UK37 and UK’37 (Brassell et  al.  1986; Prahl and Wakeham  1987). LCA temperature reconstructions from freshwater lakes are often used to indicate relative temperature changes since global lacustrine LCA calibrations are complicated by factors such as water chemistry and species effects (e.g. Toney et al. 2010). However, the production of regional calibrations, using analyses of contemporary distributions and abundances in space for time substitution, has facilitated high-­quality lacustrine LCA temperature reconstructions (e.g. D’Andrea et  al.  2011; Longo et  al.  2016). For example, temperature reconstructions in West Greenland obtained using in-­situ LCA-­temperature calibrations demonstrate a link between large and abrupt temperature changes and archaeological records of settlement and abandonment of Saqqaq, Dorset, and Norse cultures in Western Greenland (D’Andrea et al. 2011). GDGTs, produced by archaea and bacteria, can also be used as palaeothermometers since their chemical structures are temperature-­dependent (Castañeda and Schouten 2011; Tierney  2012). These indicators were initially used in marine contexts but more recently have been developed in lakes and peat sequences. Recent advances include the new peat-­specific GDGT mean annual air temperature calibration (MAATpeat), which was created using a global dataset of peatland GDGTs (Naafs et al. 2017). While the errors associated with these climate reconstruction techniques are quite large, they can be effective when temperature

­Lake Sediment Record 

shifts in the palaeoenvironmental record are of sufficient magnitude, such as during the Lateglacial-­Holocene transition. Sedimentary Ancient DNA (sedaDNA) Analysis

Environmental DNA preserved in sedimentary deposits has proved a useful new tool for studying change in terrestrial ecosystems over time. As organisms interact with their surroundings, they routinely expel their DNA into the environment through the shedding of leaves or plant rootlets (e.g. Willerslev et al. 2007), urine or faeces (e.g. Valiere and Taberlet 2000; Andersen et al. 2012), hair (e.g. Lydolph et  al.  2005; Gilbert et  al.  2007), skin flakes (e.g. Swanson et  al.  2006), feathers (e.g. Hogan et  al.  2008), saliva (e.g. Nichols et  al.  2012) or other secretive body fluids (e.g. Ficetola et al. 2008). This expelled DNA can then become incorporated into sedimentary samples such as lake and peat deposits, with a single sample having the potential to contain DNA from a variety of organisms, including plants, mammals, fish, fungi, and bacteria. DNA preserved within sedimentary samples is termed sedimentary DNA (sedDNA) or, if the samples originate from ancient environmental contexts, sedimentary ancient DNA (sedaDNA). In living organisms, damage to their DNA occurs quite frequently (e.g. during exposure to UV radiation), but this damage is repaired via an array of repair pathways (Iyama and Wilson  2013). When an organism dies, damage to its DNA still occurs, but the repair pathways no longer function and enzymes secreted by decomposers break strands apart. Consequently, most surviving DNA strands in ancient samples are short, often fewer than 100 base pairs (bp), and typically contain a variety of chemical modifications (Pääbo 1989; Sawyer et al. 2012; Shapiro et  al.  2019, see section  5). The extent of DNA damage is sample-­dependent and is linked to preservation conditions. Cold and temperature-­stable environments such as permafrost-­affected sediments and cave deposits tend to provide the best conditions for the preservation of ancient DNA (Poinar and Stankiewicz  1999; Willerslev et al. 2004, 2014; Schwarz et al. 2009). In sediments, DNA can be present within intact cells in animal and plant remains that have become embedded in the sediment matrix (Nagler et al. 2018), but it can also be released from cells (through cell lysis) and adsorbed onto mineral and organic components (extracellular DNA). Fine-­grained sediments tend to be highly suitable for the preservation of sedaDNA since extracellular DNA can bind to the charged surface areas of clay colloids (Pietramellara et al. 2001; Cai et al. 2006). In lakes, the often anoxic conditions in bottom waters and/or below 1–2 cm sediment depth appear to be highly favourable for the preservation of extracellular DNA

(Sobek et  al.  2009). Unlike unfrozen soil columns (Poté et al. 2007) and cave sediments (Haile et al. 2007), vertical migration (leaching) of DNA should not be a problem within lake sediment columns (Pansu et al. 2015; Parducci et  al.  2017). Where sediments are permanently saturated and bottom waters anoxic, burrowing animals are virtually excluded, which minimizes bioturbation. Sjögren et  al. (2017) demonstrated this was the case for 210Pb-­dated short cores that documented afforestation of the landscape in a temporally accurate sequence. The few studies that have attempted to relate DNA from lake-­sediment surface samples to surrounding vegetation suggest that the DNA signal originates from within the lake’s hydrological catchment (Sjögren et  al.  2017; Alsos et al. 2018). The presence of inflowing streams, and thus the size of the hydrologic catchment, may greatly affect the range of taxa recorded. In north Norway, Alsos et al. (2018) studied small lakes without significant inflows. The most likely taxa to appear in the DNA record were aquatic macrophytes (or in some cases aquatic algae) and terrestrial plant taxa growing at or near the lake margin (200 but 6,400 pottery sherds from >150 sites from Europe, the Near East and North Africa dating between 7000 and 2000 bce demonstrated the rarity of beeswax residues in the archaeological record (Roffet-­Salque et  al.  2015). Moreover, the absence of beeswax at sites located in the Northern latitudes suggests that the biogeography of A. mellifera did not extend to this region during the Holocene due to ecological conditions that did not support bees. Beeswax exploitation is attested continuously in Near Eastern and European contexts from the seventh-­millennium bce onwards, with beehive products likely to have fulfilled a variety of technological and cultural functions in prehistory (see Section Vessel Technology and Use). However, beeswax is often assumed to act as a proxy for the processing (cooking) or storage of honey itself, a rare source of sweetener in prehistory, probably produced as a remnant from the manual separation of honey from honeycombs (Roffet-­Salque et al. 2015). While iconographic evidence of bee exploitation is somewhat elusive in the archaeological record (Crane 1983), the study of pottery vessels and the detection of beeswax provides strong evidence for the use of beeswax products. Recent work has provided insights into the question of beekeeping vs. honey-­hunting, with lipid residues from one-­third of Nok culture (Nigeria) vessels suggesting honey collecting in prehistoric West Africa 3500 years ago (Dunne et al. 2021).

­Beyond Subsistence Technological Uses of Natural Resources Vessel Technology and Use

Organic residue analysis can be used to identify various technologies used in the production (including sealing and decoration), use and repair of ceramic vessels

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(Evershed  2008a; Roffet-­Salque et  al.  2017). A range of known vessel sealants, in use from the Neolithic onwards, include birch bark tar and other plant resins/pitches (Urem-­Kotsou et  al.  2002; Regert et  al.  2003; Reber and Hart 2008; Stacey et al. 2010; Correa-­Ascencio et al. 2014; Urem-­Kotsou et al. 2018) and bitumen (Stern et al. 2008; Connan et  al.  2013), as well as beeswax (Knappett et al. 2005; Salque et al. 2013, 2015). Such tars and pitches are often mixed with animal fats and beeswax, presumably to alter the properties of the mixture (Regert 2004; Rageot et  al.  2015). Birch bark tar and bitumen have also been used as adhesives to repair ceramic vessels, namely a Roman Ecton Ware jar from West Cotton, Northamptonshire, and bowls from Tall-­e Abu Chizan, a fifth-­millennium bce prehistoric settlement from Southwestern Iran, respectively (Charters et  al.  1993b; Connan et  al.  2008). Lastly, decoration applied to vessels at Late Neolithic Tell Sabi Abyad, Northern Syria, comprised bitumen, originating from two different source areas of Northern Iraq, implying long-­distance trade networks (Connan et al. 2004). The earliest evidence for specialization in pottery use to have been confirmed through organic residue analysis came from the analysis of Early Neolithic perforated pottery sherds, excavated from sites occupied by the first Central European farmers. The identification of dairy fats, in conjunction with the specific (sieve) vessel shape, provided compelling evidence for prehistoric cheese-­making in the sixth-­millennium bce (Salque et  al.  2013). Furthermore, investigations of the possible function of Roman mortaria, found in Britain from the Late Iron Age, revealed that they were used to process products of both plant and animal origin. Interestingly, plant-­derived residues were observed in high frequency in the mortaria (60–90%) which, together with lower lipid concentrations, perhaps reflects their use as multi-­purpose ‘mixing-­bowls’ for resource preparation involving animal and plant products (Cramp et al. 2011). There are numerous other such examples now showing specialized uses for specific vessel types (e.g. Correa-­Ascencio et  al.  2014; Casanova et al. 2020c; Dunne et al. 2020b; Stojanovski et al. 2020a). Vessels themselves are also used for technological purposes; for example, the investigation of lamps from Minoan Crete, showing the use of beeswax as an illuminant (Evershed et al. 1997c), in contrast to the use of tallow in Saxo-­Norman pottery lamps at Berkeley, Gloucestershire (Blinkhorn et  al.  2017) and in medieval lamps from Causeway Lane, Leicester (Mottram et al. 1999). Ceramic pots have also been used for the production of tar by pyrolysis and/or distillation of birch and pine bark (Heron et al. 1991; Regert et al. 2003; Lucquin et al. 2007; Urem-­ Kotsou et al. 2018; Stacey et al. 2020). Another instance of vessel specialization was found from analysis of combed

ware containers, notable for the grooves which covered half of the internal surface, found on rural sites across Ancient Greece (Evershed et al. 2003). Characteristic combinations of beeswax-­derived lipids suggested these were used as beehives, although it had previously been argued that they were too small for this purpose (Evershed et al. 2003). The Use of Natural Products in Antiquity

Organic residue analysis has been used to identify a range of natural products, including plant resins and bitumen, associated with artefacts and contexts as diverse as the pine tar identified on King Henry VIII’s flagship (1509–1545 ce), the Mary Rose (Evershed et al. 1985) to the chewing gum found across prehistoric Europe (Heron et  al.  1991; Karg et al. 2014). Resins can be identified chemically based on diagnostic higher molecular weight components in the resin fraction, known as sesqui-­ (C15), di-­ (C20), and tri-­ (C30) terpenoid biomarkers. These are resistant to degradation, meaning they often survive well in the archaeological record. Significantly, these can often be linked to the botanical family of origin, and sometimes to genus (Stern et al. 2003; Regert et al. 2008), allowing their geographical origin to be pinpointed where these plants are geographically restricted. Furthermore, the distillation of resins can produce biomarkers, such as methyl dehydroabietic acid, denoting the production of tars and pitches (Regert  2004; Rageot et al. 2018). The most common class of biomarkers used to identify bitumen are the steranes and terpanes, which, combined with isotopic values (δ13C and δ2H) of individual compounds by GC-­C-­IRMS, often allows the identification of bitumen to a geographical source (Connan 1999). Resins and bitumen have been found in burial contexts. For example, frankincense was identified, based on the presence of boswellic acids, in the cosmetic unguent found in the Pharonic tomb of Princess Sat mer Hout (c.1897–1844 bce, XIIth Dynasty) in Dahshour, Egypt (Mathe et al. 2004). In Roman Britain, resinous exudates, including coniferous resin, mastic/terebinth resin from the Mediterranean, and frankincense from Southern Arabia or Eastern Africa, were used in mortuary rites (Brettell et  al.  2014,  2015). Resins and bitumen were also widely used in Pharaonic and Graeco-­Roman Egyptian mummification practices, often in conjunction with animal fats, vegetable oils, and beeswax (e.g. Serpico and White  1998; Colombini et  al.  2000; Buckley and Evershed  2001; Buckley et  al.  2004; Clark et al. 2013; Jones et al. 2014) and as varnishes on sarcophagi, shabti boxes, Canopic cases and tomb walls (Serpico and White 2001). Organic residue analysis has also been used to identify aromatic resins, likely used as incense. These include the

­Beyond Subsistenc 

detection of 24-­nortriterpenoids, formed from boswellic acid during pyrolysis, in perforated funerary pots dating between the eleventh and fifteenth centuries CE from Belgium, confirming frankincense was the main incense ingredient found in the vessels. Frankincense resin was also identified in Post-­Meroitic levels (c.400–500 ce) at the site of Qasr Ibrîm, Egypt (Evershed et al. 1997d; van Bergen et al. 1997b). As frankincense-­bearing trees are not found in the region, it must have been exported from the nearest locations, either Northern Somalia or Southern Arabia. Copal from Zanzibar was found in a seventh to eighth century CE brass incense burner at the trading port of Unguja Ukuu, Zanzibar, Tanzania (Crowther et  al.  2015). Fossil resins, such as amber, can be identified using characteristic biomarkers, i.e. succinic acid, and distinctive Fourier-­ transform infrared (FTIR) spectra (including the presence of ‘Baltic shoulder’ in the absorption band; Beck et al. 2007), as evidenced by the remarkable lion head vessel, likely made from Baltic amber, found in a Late Bronze Age royal tomb in Syria (Mukherjee et al. 2008). In antiquity, organic dyes and pigments, produced from various flora and fauna, including roots, berries, wood, bark and leaves from plants, lichen, insects, and molluscs (Ferreira et  al.  2004) were used for cosmetic, medicinal, and funerary purposes and also to decorate or dye various media such as textiles, paintings and other art objects, manuscripts and ceramics (Mills and White  1994; Rosenberg 2008). Consequently, chemical analyses of these objects have contributed significantly to our knowledge both of prehistoric dyestuffs and also the technologies involved in their production (Good  2001; Degano et al. 2009; Ferreira et al. 2009). Various techniques such as matrix-­assisted laser desorption/ionization (MALDI), direct exposure mass spectrometry (DE-­MS), laser desorption/ionization-­mass spectrometry (LDI-­MS), direct analysis in real-­time  – time of flight mass spectrometry (DART-­ToF-­MS) and time of flight-­secondary ion mass spectrometry (ToF-­SIMS) have been applied in the analysis of organic dyes (see Degano et  al. (2009) for a review). These have the advantage of needing only very small sample sizes (a few nano/micrograms), minimal sample handling, and no pretreatment, lessening the risk of sample contamination. Notable examples include textile from a high-­status tomb in the Bronze Age palace at Qatna, Syria, dyed using Royal Purple made from shellfish glands from Hexaplex trunculus (James et al. 2009) and the use of Royal Purple as a funerary make-­up in a third century CE Gallo– Roman burial at Naintré, France (Devièse et  al.  2011). Analysis of Iron Age Scandinavian bog textiles revealed the presence of luteolin, indicating a yellow dye and indigotin, a blue dye, and, possibly, lichen dyes (Vanden Berghe et al. 2009).

Dating of Single Lipid Compounds The direct dating of archaeological lipids has opened up an exciting new avenue in archaeological dating. The new method is currently focused on the direct dating of lipids extracted from archaeological pottery (commonly the C16:0 and C18:0 fatty acids deriving from animal fats), allowing the period of use of the vessels to be directly dated. The new technique will also help in resolving the chronologies of archaeological sites where no conventional material for dating (e.g. bones, seeds, charcoal) is present. One striking example of this was the dating of the earliest Neolithic in the city of London. The recent find of four pits containing Early Neolithic pottery was exceptional, due to the impact of later Roman occupation, but a lack of organic material in these pits prevented absolute dating. Thus, the extraction and dating of lipids from the Early Neolithic vessels demonstrated both the importance of dairy products to these first farmers, and also offered an unprecedented opportunity to gain insight into the ancestry of a major world capital, the city of London from the fourth-­millennium bce (Casanova et  al.  2020a: figure  8). A further case study from a megalithic monument dating to the third-­millennium bce in Portugal provided calendrical ages on an otherwise non-­ datable site of importance (Stojanovski et al. 2020a). Secondly, as pottery typologies and seriation studies are commonly used to build relative chronologies of reference, direct dating of the pottery through their lipid residues permits these chronologies to be directly refined. The potential of such an approach was tested on Middle Neolithic groups from Eastern France (Casanova et  al.  2020a: figure  3), for which the chronology has been previously resolved using pottery seriation and over 90 radiocarbon dates from articulated bones and charcoal (Denaire et al. 2017: figures 10, 15 and 16). The dates on lipids from four potsherds (fitting within the regional seriation) are entirely compatible with those building the existing chronology, supporting the use of direct dating of pottery vessels (in significant numbers) for the purpose of directly refining typo-­chronologies. Furthermore, the antiquity of lipids within pottery is now verifiable, and it is particularly relevant in instances where lipid analyses and the archaeological record do not match. For instance, a study on ethnographic Samburu pastoralists in Kenya showed the group only used clay pottery during feasting events for cooking meat, and dairy products were exclusively stored in gourds (Dunne et  al.  2019b). Lipid analyses of clay potsherds recovered from surface contexts revealed, however, that a significant number of pottery vessels contained a dairy signal (Dunne et al. 2019b: figure 4). Direct dating of those dairy residues demonstrated that the lipids of this particular site were of a historical origin, rather than ethnographic, shedding light on the surprising lipid

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results. Another impactful study was the dating of dairy residues from hunter-­gatherer ­pottery vessels in the highlands of Lesotho (Fewlass et  al.  2020). A disagreement between morphological and ancient DNA evidence regarding the presence of domesticated sheep at the site ran for years. Analysis of lipids preserved in pottery provided a new line of evidence for the access of these hunter-­gatherers to domesticated species due to the presence of dairy residues in the pottery (Fewlass et al. 2020: figure 3). Direct dating of these residues permitted the dairy signal to be anchored in the known timeframe of these hunter-­gatherer groups, supporting evidence for their access to domesticated animals. Finally, direct dating of specific foodstuffs is now possible, providing direct evidence for the use – and start of use – of specific food commodities. This has illustrated the timing of the appearance of dairy product exploitation in Central Europe during the sixth-­millennium bce (Casanova et  al. 2020a: figure 9, 2020c, 2021a) and the Balkans (Stojanovski et al. 2020b, p. 7), supporting the hypothesis that dairying was in use by the earliest Neolithic populations in the studied regions. Equine lipids extracted from pottery excavated from two sites in Kazakhstan were also successfully dated (Casanova et al. 2022). Additionally, the processing of marine products was investigated at a well-­dated Viking site, with known use of marine resources (Casanova et al. 2020b). Importantly, this case study revealed that marine product exploitation can be detected by the presence of a reservoir effect in the radiocarbon measurements, i.e. the occurrence of apparently-­older radiocarbon dates for the pottery fatty acids compared to the known age of the site, due to the contribution of marine sources to the pottery lipids. Reservoir effects in the fatty acid 14C measurements are observed even in instances where the characteristic aquatic biomarkers do not survive and thus, the occurrence of apparently too-­old dates for pottery fatty acids can be used as a tracer for detecting the exploitation of marine resources. Even more interestingly, this raises the potential that radiocarbon dates could be used to more precisely estimate the mixing of terrestrial and marine products in the same potsherds, providing new insights on the exploitation and mixing of different food resources. Other food commodities processed in pottery vessels, such as bee products or plants, could be datable using CSRA, through targeting different classes of lipids such as n-­alkanes. Furthermore, this method can also be applied to other matrices. For instance, the direct dating of lipids in coprolites could provide the age of ancient human occupations where human bones do not survive, and the dating of bone lipids could be used as an alternative in cases where bone collagen is poorly preserved. In conclusion, single lipid dating can provide answers to a wide range of archaeological and chronological questions.

Palaeoclimatic Information Animal tissues record the hydrogen isotope composition of environmental water obtained from plants and drinking water in their fatty acids. This forms the basis of studies exploiting the predictable changes in the δ2H values of precipitation through time and space as described by the Global Network of Isotopes in Precipitation (GNIP; http:// www-­naweb.iaea.org/napc/ih/IHS_resources_gnip.html). Seasonal variations in the H isotope signal in precipitation underpin the identification of mares’ milk in the archaeological record. As horses are non-­ruminants, carcass and milk fats cannot be distinguished based on their carbon isotope composition. However, as it is only produced in spring and summer, mares’ milk displays a ‘summer δ2H signal’ (relatively enriched δ2H values) compared to meat (more depleted yearly signal). Mares’ milk was detected at the site of Botai, Kazakhstan, dated to c.3500 bce (Outram et al. 2009) using this proxy. The faunal assemblage at this Eneolithic site is almost completely composed of horse remains and animal lipids extracted from pottery displayed a non-­ruminant signature based on their δ13C values. By measuring their δ2H values using GC-­thermal combustion-­ IRMS (or GC-­TC-­IRMS), animal fats with relatively enriched δ2H values were interpreted as arising from mares’ milk, while the remainder were interpreted as horse carcass fats. Together with skeletal markers (bit wear and small size of the animals), the identification of mares’ milk provided evidence for the early domestication of horses at Botai (Outram et al. 2009). A similar approach was adopted for Ukrainian sites, although the limited variation in seasonal δ2H values of precipitation at the sites prevented the successful identification of mares’ milk (Mileto et al. 2017). While δ2H (and δ18O) values of precipitation vary seasonally, they also record changes in climate through time (Johnsen et al. 1992). A recent study by Roffet-­Salque et al. (2018) aimed to record the δ2H values of well-­dated archaeological animal fats extracted from pottery vessels, to build a local palaeoclimate record at the actual site of human activity in the past. The TP area at the site of Çatalhöyük was occupied before, during, and after the abrupt climate event at 8.2 kyr BP. It was shown that animal fats from the site recorded a shift in their δ2H values synchronous with this event. Archaeo(zoo)logical evidence at the site suggests that people at Çatalhöyük underwent a period of change at that time. Simulations using climate models suggest an overall cooling and a decrease in summer rainfall that could have increased livestock nutritional requirements and thus been detrimental to agriculture (Roffet-­ Salque et al. 2018). This is the first example of building a palaeoclimatic record based on δ2H values of lipids; however, this method is still in its infancy. Understanding the

­Concluding Remark  545

factors governing the routing of H from the feed and water to the animal’s tissues will be crucial to interpret the H signals and study the impacts of climate change on ancient populations.

­Concluding Remarks As illustrated above, the last 20 years have seen lipid analysis in archaeology elevated from an approach regarded by many as of somewhat marginal or niche value, to a toolkit of proven and rapidly evolving methodologies, with the potential to make significant contributions across the gamut of archaeology, in all periods and all regions of the world where humans have left their mark in the past. Its primary value up to now has been in the investigation of diet, animal husbandry, hunting, and fishing, due to the widespread survival of animal fats in archaeological pottery. The introduction of the high throughput lipid extraction approach (Correa-­Ascencio and Evershed  2014) is transforming the way this area is being approached, since large numbers of samples can be processed rapidly and efficiently. This step change in sample processing power allows archaeological questions comprising multiple variables to be tackled, e.g. diachronic changes at a multi-­phase site, synchronicity in activities through multi-­site studies across regions, form versus function investigations of vessels, etc. The result is that there is an emerging trend in published papers focussing on the analysis of hundreds to thousands of samples rather than a few tens being taken to represent a site, period, or geographical region. Surveying greater numbers of sherds increases the chances of capturing the widest possible range of uses of pottery vessels and assessing variability statistically. This move towards increasing the sample numbers in archaeological investigations involving all types of material is a trend that is to be encouraged. Instrumental advances have been crucial in driving advances in lipid analysis. The last 20 years have seen the uptake of methods that link the structure of lipids to their isotope compositions. The capability for compound-­specific stable isotope analysis by GC-­C-­IRMS allows the routine determination of δ13C values of individual lipids. Armed with this technique researchers have been able to exploit the natural variations in carbon isotope signatures manifested by variations in carbon cycling in different environments and differences in carbon metabolism in different animals and plants. Most notable has been the use of this approach in identifying the sources of animal fat residues, i.e. ruminant versus non-­ruminant, ruminant carcass versus dairy, and aquatic versus terrestrial, providing insights into husbandry practices, notably dairying (e.g. Copley

et  al.  2003; Craig et  al.  2005; Evershed et  al.  2008a, 2022; Dunne et al. 2012, 2020a) and the exploitation of terrestrial versus aquatic resources (Cramp and Evershed 2014). Advances in AMS instrumentation and the associated sample preparation facilities have brought the 14C dating of individual lipids into the domain of archaeology (Casanova et  al.  2020a). While pottery-­derived fatty acids have been the main targets up to now, we anticipate that this approach will find applications in the 14C-­dating of lipids preserved in human and animal remains, and soils and sediments. As a footnote – while compound-­specific 14C analysis has been widely applied in other areas of environmental chemistry, it is a fact that archaeology sets the most demanding standards in terms of precision and accuracy, which meant new approaches to sample handling and the elimination of  contamination had to be developed (Casanova et  al. 2017, 2018) and these developments are set to benefit our sister disciplines. As investigations of lipids have moved to geographical regions and periods when plants would have featured prominently in the human diet, stable carbon isotope signatures help to confirm their origins in C3 or C4 plants (e.g. Dunne et al. 2016). Additionally, and critically for assessments of plant exploitation, has been the development of a new generation of GC/MS instruments, notably the GC-­Q-­ ToF-­MS discussed above. These new instruments are transforming the way complex lipid assemblages presented by archaeology can be dissected and exploited to expand the range of commodities and activities that can be revealed. These instruments offer hitherto unobtainable specificity and selectivity due to their capability to define elemental compositions of analytes, something only dreamt of 20 years ago when the previous edition of the Handbook of Archaeological Sciences was published. The result is that we are already beginning to see examples of how such instrumentation can be used to reveal new molecular proxies, e.g. for cereal exploitation (Hammann and Cramp 2018). A feature of high throughput analysis protocols, greater automation, and the comprehensive nature of the data acquired by GC-­Q -­ToF-­MS instruments, for example, is the sheer volume of information recorded. Here we enter the world of ‘big data’, which requires the application of computational methods to effectively interrogate data sets that are so large that they defy what can be achieved manually in terms of time and multi-­dimensionality. Data-­mining ‘omic’-­style workflows taking advantage of automated deconvolution from high resolution GC/MS data offer the  only realistic solution to post-­run processing (Korf et al. 2020). While compound-­specific stable carbon isotope values provide another level of diagnosis in assigning the types of plant exploited, they also raise the possibility of using lipids

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preserved at archaeological sites as climate proxies by linking plant lipid isotope values to climate-­driven vegetation change. In regions where the shifts in plant ecological assemblages were more subtle and did not involve C4 plants, the capability exists for the determination of individual lipid hydrogen isotope compositions using GC-­TC-­ IRMS. The first demonstration of this proxy was seen in recent work linking variations in precipitation recorded in δ2H values at Çatalhöyük with the Laurentide ice sheet collapse 8,200 years ago (Roffet-­Salque et al. 2018). The obvious advantage of undertaking such an approach is the ability to link changes in human behaviour to climate proxies recorded in archives recovered from the very sites where people lived, with the attendent advantage of accurate 14C dating of the events based on the lipids themselves. The future application of lipids in archaeology is extremely bright with the toolkit we currently have available and is being made all the brighter by the new methods and instruments that are continually emerging. With the proliferation of archaeological lipid analysis technologies,

opportunities exist to take applications in many new directions. In prehistory, the value has been recognized of linking lipid with other proxies, notably those from zooarchaeology (Outram et al. 2009; Debono Spiteri et al. 2016) and palaeobotany (Dunne et al. 2016), to improve robustness or increase levels of interpretation. This is a trend that is set to continue, especially with more recent directions of archaeological research involving the meta-­analysis of robustly-­constructed and substantial databases (e.g. the EuroEvol dataset: Colledge 2016; Manning 2016; Manning et al. 2016). Whilst lipid analysis has had its major impact up to now within the field of prehistoric research, considerable scope exists to connect applications to historical periods. Combining the complementary lines of evidence from such periods (e.g. historical texts) with new techniques and big data approaches, raises the potential to explore diverse phenomena in more complex societies. In so doing, an exciting new range of socio-­cultural, economic, and environmental questions relating to past human beliefs and practices is opened up.

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27 Archaeological Microbiology Laura S. Weyrich1,2,3,4 and Vilma Pérez3,4 1

Department of Anthropology, The Pennsylvania State University, University Park, PA, USA Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, USA 3 Australian Centre for Ancient DNA (ACAD), University of Adelaide, Adelaide, South Australia, Australia 4 ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH), University of Adelaide, Adelaide, South Australia, Australia 2

Archaeological microbiology is an emerging, interdisciplinary area of archaeological science, where information from bacteria, archaea, viruses, parasites, and protozoans provides new insights into the past. A microbe can rapidly respond to environmental, anthropogenic, and climatic change, as it typically replicates much faster than multicellular organisms, providing unique perceptions into how our planet has changed over time. This microbial information, literally previously invisible to the naked eye, has been successfully retrieved from a wide-­variety of archaeological specimens, including soil, ice, calcium carbonate, stone tools, pottery, human bone and tissue, dental calculus, and more (Figure  27.1). This emerging field has the opportunity to improve our resolution and understanding of complex past processes, moving beyond ancient diseases, to reveal information on plant domestication and cultivation, food storage and preparation, environmental and climatic change, human migration, and the evolution of hominids – to name a few. A wide range of techniques, including culturing, microscopy, and genetics have been utilized to examine these microbes and their mechanisms in archaeological contexts. However, technological advancements, largely in the field of high throughput DNA sequencing, metaproteomics, metabolomics (see Box 27.1 for definitions of common terms), and other fields, have revolutionized our ability to identify specific microbes and understand how and why they adapt and respond through time. These new techniques now ensure that archaeological microbiology can support nearly every aspect of archaeological inquiry. In

this chapter, we will explore these techniques so that you can learn about techniques that can be applied to mine microbial information in an archaeological way. As this is a relatively new area of archaeological science, the limitation of methods, improvements in authentication, and contamination avoidance need further consideration before the full potential of this emerging field can be realized. The field is currently plagued with early publications that lack robust authentication or are riddled with contamination concerns. Understanding these issues will improve the quality of emerging data and accurately apply microbiological concepts in archaeology in novel, yet unforeseen, ways. In this chapter, we will examine how the use of ancient DNA has emerged as a tool with great promise to revolutionize the application of bacteria in archaeology, moving microbial archaeology to a field well beyond the singular study of human diseases. We will examine the previous and emerging technologies that are used to identify and study single ancient microorganisms, as well as complex mixtures of microbes – microbiomes. We will also discuss the restrictions and limitations of these techniques that need to be considered when studying ancient microorganisms, especially from environmental samples. We will then summarize many exciting new lines of archaeological inquiry, exploring how microbes have informed inquiry into how, where, why, and to what extend humans lived and came to be on this planet. Lastly, we will comment on the uses of palaeomicrobiology moving forward and emphasize new areas of thought in this emerging field.

Handbook of Archaeological Sciences, Second Edition. Edited by A. Mark Pollard, Ruth Ann Armitage, and Cheryl A. Makarewicz. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd.

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Biological samples for paleomicrobiological analysis

Sediment, soil, or environmental Samples

Animal or human remains

Ice cores

Stone tools

Pottery

Rock paintings

Dental calculus

With contamination

Environment Archaeological sites; sediment; water; excavation tools; archaeologist; other samples; etc.

Storage Storage with other samples; microbial growth; water damage; dust; sample curators; etc.

Laboratory Lab plastic wear; lab reagents; air flow; technicians; cross contamination from other samples; etc.

Paleomicrobiological signal Figure 27.1  Summary of all sample types currently utilized in microbial archaeology and how contamination can alter the signal present in ancient and historic specimens.

Box 27.1  Common Terms Archaeological microbiology: utilizing ancient and historic microorganisms to reveal information about past human biology, lifeways, and environments. Microbe: (i.e. microorganism) a tiny living, typically single-­ celled organism, such as a bacterium, archaea, virus, fungi, parasite, or protozoan. Microbiota: a community or microorganisms that live together in a specified niche. Microbiome: a community of microorganisms and its environmental and genomic context that lives together in a certain location or niche. Palaeomicrobiology: the study of ancient microorganisms using DNA, proteins, or chemicals. High Throughput DNA Sequencing (HTS): the ability to  sequencing millions of DNA molecules simul­ taneously. Immunohistological methods: approaches that utilize the binding of antibodies to a known target for identification of certain microbes or materials.

Metagenomics: the use of DNA sequencing to concurrently study of many genomes present in a sample; For example, sequencing DNA from the bacteria, viruses, archaea, human cells, and food particles present in ancient dental calculus. Proteomics: the use of mass spectroscopy to examine proteins present in a microbiome Metabolomics: the study of chromatography and mass spectroscopy to identify chemicals and small molecules emitted by a microbiome. Metatranscriptomics: the examination of all the RNA molecules produced by cells under certain conditions or at certain times Strains: different versions of the same microbial species, typically demarcated by a handful of mutations within their genome. Symbiotic microbe: a microorganism that lives with its host, and the microbe and host both provide benefits for one another without causing each other harm.

­Tools and Techniques Used in Archaeological

­ ools and Techniques Used T in Archaeological Microbiology Older Methods: The Beginning of Archaeological Microbiology Historical Accounts and Records

Prior to scientific proofs and the establishment of archaeological microbiology, historical accounts constituted the backbone of research, especially in the field of epidemiology. The philosophers and scientists Hippocrates (470–400 bce), Thucydides (460–395 bce), and Marcus Terrentius Varro (116–27 bce) were the first to provide some understanding to ancient civilizations that diseases could be caused and transmitted by invisible forces, now known as microbes (Cox  2002; Yapijakis  2009; Hempelmann and Krafts 2013). Furthermore, they also began the practice of taking notes on the signs and symptoms of sick people, constituting the first historical records of ancient diseases (Maczulak  2011). Certainly, there were many epidemics that occurred in the ancient world that were not recorded, but numerous historical accounts of plagues exist, such as the three great plagues of the ancient world: the Plague of Athens (430–426 bce), the Antonine Plague (165–180 ce) and the Justinian Plague (541–549 ce) (Raoult and Drancourt 2008). One of the most historically recorded diseases is the bubonic plague, which, thanks to historical records, we know began around 541 ce and continued into the nineteenth century (Spyrou et al. 2019). These written accounts have information about the place, season, extent of the epidemic, mortality, and clinical sequelae of the diseases, playing a vital role in the determination of the etymologies of ancient diseases (Bollet  2004; Cunha and Cunha  2008). Nevertheless, the interpretation of these ancient descriptions often presents a number of challenges, such as variation in their translation, which limits the  accurate determination of the causative agent (Shrewsbury 1950; Parry 1969). Currently, the best way to confidently demonstrate the involvement of a certain pathogen in ancient diseases is the combination of historical records with palaeomicrobiology methods (Raoult and Drancourt 2008). Culturing

Investigating ancient microbes is not a recent phenomenon and may go back as far as the 1920s, when attempts to isolate microbes from coal dating back millions of years were undertaken (Lipman 1928). However, it was not truly recognized as a scientific field during the first half of the twentieth century, due in large part to scepticism about the likelihood that microorganisms could survive through deep time. Despite these controversial results, several

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studies still aimed to isolate viable ancient microbes from different sources (e.g. prehistoric amber and permafrost samples), claiming that one of the biggest advantages is that it would allow examination of their metabolic capabilities (Cano and Borucki  1995; Zhang et  al.  2013; Goncharov et al. 2016). While some of these studies have gained acceptance, most of them have been widely criticized due to vast discrepancies in results and accusations of data falsification (for examples, see Nickle et  al.  2002; Willerslev and Hebsgaard  2005; Eisenhofer et  al.  2016; Eisenhofer and Weyrich 2018). Previous findings have not been independently replicated nor validated through stringent authentication methods such as evolutionary rate tests (Cano and Borucki 1995; Zhang et al. 2013; Goncharov et al. 2016; Margesin et al. 2016). Furthermore, modern or environmental contamination of ancient remains during sampling or laboratory analysis is highly probable (Hebsgaard et al. 2005; Eisenhofer et al. 2016). Thus, the resuscitation of microorganisms from these samples seems rather difficult and unlikely. Microscopy

Microscopy techniques represent important sources of new information and re-­evaluation of older discoveries in  microbial archaeological studies (Figure  27.2). Early palaeomicrobiology studies relied on morphological approaches, facilitating the characterization of ancient microorganisms, without the need of previous isolation (Swain  1969). One of the first microscopy-­based studies of  ancient microorganisms was on human-­associated microbes preserved within archaeological dental calculus (covered extensively in Chapter 28); this study, performed by Dobney and Brothwell (1986,  1988), showed the presence of calcified rod-­shaped microorganisms using scanning electron microscopy (SEM) from English medieval times. In addition, microscopy has been widely applied to parasitological studies of mummies and coprolites, allowing researchers to compare epidemiological patterns in both ancient and modern populations (Reinhard and Bryant (1992); see also Chapter  38). The use of several types of microscopy (e.g. light microscopy, electron microscopy) has been employed since the 1960s to study microbes not only in archaeological context, but further back in time, to studies of the earth’s oldest microfossils (e.g. early and late Precambrian, Devonian, and Eocene sedimentary rocks) (Swain  1969; Javaux et  al.  2004; Baumgartner et  al.  2019). While these approaches paved the way for modern palaeomicrobiology as we know it today, they lack the ability to identify specific microbes; for example, many bacteria have the same shape and are roughly the same size, making it nearly impossible to ­identify a disease-­causing microbe from a beneficial one.

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Archaeological Microbiology

Methods

Old Methods

New technologies

Advantages

Challenges • Variation in translation and interpretation • Limited accurate determination of causative agents

Historical accounts and records

• Determination of etymologies of ancient diseases • Provide historical context

Culturing

• Examine metabolic capabilities of ancient microbes

• Resuscitation of ancient microbes is difficult and unlikely • High rates of contamination

Microscopy

• No need of previous isolation and culturing

• Lack of ability to identify specific microbes

Immunohistochemistry

• No need of previous isolation and culturing

• Provide initial identification of microbes but not subspecies level

Genetic approaches using PCR

• No need of previous culturing • Detection of more ancient microbes • Specific detection of ancient microbes

• PCR inhibition by damage and fragmentation of aDNA • High rates of contamination

Metagenomics (next generation Sequencing)

• Large amounts of data • More informative genetic approach • Specific detection of ancient microbes

• High rates of contamination • Insufficient reference databases

Metaproteomics

• Large amount of data • Provide functional information • Specific detection of ancient microbes

• Further standardization • Lack of replicability • Insufficient reference databases

Metabolomics

• Provide functional information • Closer link to phenotype of ancient microbe

• Further standardization • Lack of replicability • Insufficient reference databases

Figure 27.2  An overview of the current methodologies applied within microbial archaeology, along with their advantages and challenges.

Tools that apply genetic or genomic approaches have provided species-­specific resolutions. Immunohistochemistry

Immunohistological methods (e.g. immunohistochemistry, immunofluorescence) have been successfully employed in palaeomicrobiology, especially palaeopathological studies (Figure 27.2). Depending on tissue storage conditions, the antigenic properties in ancient remains can be preserved, allowing the specific detection of microorganisms. Immunohistochemistry and immunochromatography have been used to detect bacteria in human remains, such as Tropheryma whipplei and Rickettsia rickettsii in paraffin blocks from autopsy cases dating to one century ago, Yersinia pestis in ancient plague skeletons, and viruses and parasites in mummies (reviewed in Lepidi (2008)). As proteins are more resistant to environmental degradation compared to DNA, these methods are well-­suited for detecting microorganisms in ancient tissues. However, immunological assays can provide only an initial identification in some cases (Kolman et  al.  1999). For example, Treponema pallidum subspecies are morphologically

indistinguishable by immunofluorescence or electron microscopy, making the diagnostic extremely difficult and complicating further epidemiologic or phylogenetic analyses, increasing the need of genetic information (Montiel et al. 2012). Genetic Approaches Using Polymerase Chain Reaction

The invention of the polymerase chain reaction (PCR) offered a powerful solution to the logistical and time limitations of culture-­dependent and microscopy methods, allowing the detection of many organisms, including ­specific microbes. Mycobacterium tuberculosis was the first ancient microbe detected by modern biomolecular methods based on PCR, in ancient human skeletons of individuals suspected of having tuberculosis from Borneo, Cyprus, Turkey, and United Kingdom, launching palaeomicrobiology as an emerging research field (Spigelman and Lemma 1993). Since these initial findings, PCR-­based techniques have been successfully and routinely applied to archaeological material, and its fruitful interaction with modern genomic studies has helped to understand the

­Tools and Techniques Used in Archaeological

c­ ontinuous evolution of microbes. However, PCR-­based techniques are highly sensitive and need to be carefully controlled to minimize external contamination (Figure 27.2). Different protocols have been developed to help reduce the contamination and to authenticate the results, such as ­suicide PCR, where a set of target-­specific primers are only used one single time and were never used previously in any positive control PCR reaction (Raoult et  al.  2000). Nevertheless, despite refinements in experimental protocols, several inaccurate publications from PCR-­based ­studies caused mistrust in the field, highlighting the need to increase strict criteria for data validation and develop more sensitive methods (Cooper and Poinar 2000).

New Technologies: What Has Changed Over the Last 10 Years? High Throughput DNA Sequencing

At the end of the last decade, new sequencing technologies (i.e. high throughput sequencing – HTS) enabled the acquisition of gigabases of genomic information. These methods emerged as means to improve the identification of specific microbes and explore a broader range of microbial communities or mixtures (Weyrich et  al.  2015). Microbial ancient DNA studies begun to apply these techniques to increase the sensitivity and coverage of their molecular analyses, revolutionizing the field of palaeomicrobiology by revealing information that could not be assessed with previous methods (e.g. culturing methods, microscopy, immunohistochemistry). Currently, there are two primary DNA-­based approaches used to characterize the microbiome in ancient samples: amplicon sequencing (for example, 16S ribosomal rRNA metabarcoding) and shotgun metagenomics. Amplicon sequencing was used as an early tool in palaeomicrobiology, as the technique is relatively inexpensive and is an extension of the familiar PCR approaches widely used early on by the ancient DNA field. The technique involves amplifying a gene or gene region that is unique to each microbial species, serving as a barcode or fingerprint for the species within the sample; for example, researchers design primers, or sequences of DNA that guide a PCR reaction, on conserved regions that surround a unique ‘barcoding’ region of the genome (Caporaso et  al.  2011). That region is then amplified for all of the species that maintain that conserved region, allowing a single PCR reaction to be used to assess thousands of species (Caporaso et  al.  2012). For example, all bacteria and some archaea maintain a conserved sequence of DNA within the gene region that encodes the 16S ribosome RNA (Woese and Fox 1977). By examining the barcoding sequences within the 16S ribosomal encoding region of the genome,

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researchers will get a view on the different barcodes present from each species and the abundance of each type that is present. From this approach, it is possible to generally identify the types of bacteria and archaea present and get a relative estimate of how many are present in a biological sample. However, this technique has many limitations and challenges. For example, examining a barcoding region, such as the 16S rRNA region, does allow detection of most bacteria and some archaea but does not inform on different, unrelated microbes, such as viruses, fungi, or parasites. When used in ancient DNA contexts, the results may also miss some expected species and misrepresent the amounts of certain species present. This is because the primers used in standard amplicon analyses (such as Caporaso et  al. (2012)) target regions that may be longer than the typical length of aDNA fragments (e.g. targeting 500–800 bp, when the aDNA in the sample is mostly