PALEOCLIMATOLOGYReconstructing Climates of the

Quaternary

THIRD EDITION

RAYMOND S. BRADLEYUniversity of Massachusetts, Amherst, Massachusetts

AMSTERDAM • BOSTON • HEIDELBERG • LONDON

NEW YORK • OXFORD • PARIS • SAN DIEGO

SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYOAcademic Press is an imprint of Elsevier

Contents

Acknowledgments xiFront Cover Photograph xiiiForeword xvPreface to the Third Edition xix

1. Paleoclimatic Reconstruction

Introduction 1Sources of Paleoclimatic Information 4Levels of Paleoclimatic Analysis 9Modeling in Paleoclimatic Research 10

2. Climate and Climatic Variation

The Nature of Climate and ClimaticVariation 13

The Climate System 16Feedback Mechanisms 24Energy Balance of the Earth and Its

Atmosphere 27Timescales of Climatic Variation 33Variations of the Earth’s Orbital Parameters 36Solar Forcing 46Volcanic Forcing 50

3. Dating Methods I

Introduction and Overview 55Radioisotopic Methods 57

Radiocarbon Dating 59Potassium-Argon Dating (40K/40Ar) 83Uranium-Series Dating 85Luminescence Dating: Principles and

Applications 91Surface Exposure Dating 98Fission-Track Dating 100

4. Dating Methods II

Paleomagnetism 103The Earth’s Magnetic Field 104Magnetization of Rocks and Sediments 105The Paleomagnetic Timescale 107Geomagnetic Excursions 108Relative Paleointensity Variations 110SecularVariationsof theEarth’sMagneticField 111

Dating Methods Involving Chemical Changes 111Amino Acid Dating 113Obsidian Hydration Dating 124

Tephrochronology 125Biological Dating Methods 129

Lichenometry 129Dendrochronology 135

5. Ice Cores

Introduction 137Stable Isotope Analysis 141

Stable Isotopes in Water: Measurement andStandardization 143

Oxygen-18 Concentration in AtmosphericPrecipitation 144

Factors Affecting the Stable Isotope Recordin Ice Cores 145

Deuterium Excess 151Dating Ice Cores 154

Radioisotopic Methods 155Seasonal Variations and Episodic Events 155Theoretical Models 165Chronostratigraphic Correlations 167

Paleoclimatic Reconstruction from Ice Cores 167Ice-Core Records from Greenland 167Ice-Core Records from Antarctica 175Past Atmospheric Composition from

Polar Ice Cores 180

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Greenhouse Gas Records in Ice Cores 184Ice-Core Records from Low Latitudes 189

6. Marine Sediments

Introduction 196Paleoclimatic Information from Biological Material

in Ocean Cores 197Oxygen Isotope Studies of Calcareous Marine

Fauna 199Isotopic Composition of the Oceans 201Oxygen Isotope Stratigraphy 211Orbital Tuning 215Orbital Forcing: Evidence from the Marine

Record 220Sea Level Changes and d18O 222

Paleotemperatures from Relative AbundanceStudies 225

Paleotemperature Reconstruction from SedimentGeochemistry 228Paleotemperatures from Alkenones 228Paleotemperatures from TEX86 and Long-Chain

Diols 231IP25 and Related Sea Ice Proxies 234Paleotemperatures from Mg/Ca Ratios 238

Oceanographic Conditions at the Last GlacialMaximum (LGM) 239

Paleoclimatic Information from Inorganic Material inMarine Sediments 244

Thermohaline Circulation of the Oceans 248Tracers in the Ocean 252

Changes in Atmospheric Carbon Dioxide: The Role ofthe Oceans 258

Abrupt Climate Changes 263Heinrich Events 267

7. Loess

Chronology of Loess-Paleosol Sequences 284Paleoclimatic Significance of Loess-Paleosol

Sequences 287

8. Speleothems

Isotopic Variations in Speleothems 295Tropical and Subtropical Paleoclimate Variability

from Speleothems 296

Speleothems and Glacial Terminations 299Millennial to Centennial Scale Changes 302Late Glacial and Holocene Records 304Stalagmite Records of the Last Two

Millennia 310Paleoclimatic Information from Periods of Speleothem

Growth 311Speleothems as Indicators of Sea-Level

Variations 315

9. Lake Sediments

Sedimentology and Inorganic Geochemistry 320Varves 323Pollen, Macrofossils, and Phytoliths 324Ostracods 327Diatoms 327Stable Isotopes 330Organic Biomarkers 338

10. Nonmarine Geologic Evidence

Introduction 345Periglacial Features 346Snowlines and Glaciation Thresholds 351

The Climatic and Paleoclimatic Interpretation ofSnowlines and ELAs 352

The Age of Former Snowlines 356Mountain Glacier Fluctuations 358Evidence of Glacier Fluctuations 359The Record of Glacier Front Positions 360

Lake-level Fluctuations 362Hydrologic Balance Models 366Hydrologic-Energy Balance Models 370Regional Patterns of Lake-Level Fluctuations 371

11. Insects and Other Biological Evidencefrom Continental Regions

Introduction 377Insects 377

Paleoclimatic Reconstructions Based on FossilColeoptera 379

Paleoclimatic Reconstruction Based on AquaticInsects 384

Former Vegetation Distribution from PlantMacrofossils 388Arctic Tree Line Fluctuations 389

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Alpine Tree Line Fluctuations 392Lower Tree Line Fluctuations and Rodent

Middens 395Peat 400

12. Pollen

Introduction 405The Basis of Pollen Analysis 406

Pollen Grain Characteristics 408Pollen Productivity and Dispersal: The Pollen

Rain 410Sources of Fossil Pollen 410Preparation of the Samples 411Pollen Analysis of a Site: The Pollen

Diagram 411Zonation of the Pollen Diagram 414

Pollen Rain as a Representation of VegetationComposition and Climate 414Maps of Modern Pollen Data 416Mapping Vegetation Change: Isopolls and

Isochrones 418HowRapidly Does Vegetation Respond to Changes

in Climate? 422Quantitative Paleoclimatic Reconstructions Based on

Pollen Analysis 425Paleoclimatic Reconstruction from Long Quaternary

Pollen Records 434Europe 434Sabana de Bogota, Colombia 438Central American Lowlands 441Amazonia 443Equatorial and Sub-Saharan Africa 445Northeastern Siberia 449

13. Tree Rings

Introduction 453Fundamentals of Dendroclimatology 454

Sample Selection 456Cross Dating 458Standardization of Ring-Width Data 463Divergence 469Calibration of Tree-Ring Data 470

Verification of Climatic Reconstructions 476Dendroclimatic Reconstructions 480

Reconstructions of Temperatures over theNorthern Hemisphere 480

Drought Reconstruction 481Reconstruction of Atmospheric Circulation

Modes 487Wildfires and Dendroclimatology 490

Isotopic Dendroclimatology 493d18O and d2H 493d13C 495

14. Corals

Coral Records of Past Climate 499Paleoclimate from Coral Growth Rates 506Luminescence in Corals 506d18O in Corals 507d13C in Corals 510D14C in Corals 510Trace Elements in Corals 511Fossil Coral Records 512

15. Historical Documents

Introduction 517Historical Records and Their Interpretation 519

Historical Weather Observations 524Historical Records of Weather-Dependent Natural

Phenomena 526Phenological and Biological Records 534

Regional Studies Based on Historical Records 538East Asia 540Europe 544

Records of Climate Forcing Factors 545Climate Paradigms for the Last Millennium 548

Appendix A 553

Appendix B 557

References 559

Index 667

ixCONTENTS

Foreword

Earth is a constantly changing dynamicentity, composed of multiple complex phys-ical, chemical, and biological systems thatinteract on a spectrum of time and spatialscales. To comprehend the Earth System asa whole, we must understand the nature ofthese complex subsystems, both now andin the past, and identify the important link-ages among them. Earth is now experiencingmany changes, some large and more rapidthan others. To attempt predictions of howthe Earth System may change in the futurerequires an assessment of the conditions thatpreceded the present, a perspective that canonly be gained from the records of past cli-mate. Studies of the past also reveal justhow quickly some components of the EarthSystems have responded to specific external(e.g., solar) and internal (e.g., atmosphericchemistry) forcing factors. Knowledge ofthese changes and understanding their keydrivers are critical to efforts to anticipateand plan for future environmental changes.

We are very fortunate that today we havea rich body of knowledge and numerousdiverse natural systems that record manytypes of climatic and environmental infor-mation across a spectrum of temporal scales.Additionally, we now have rich array oftechnologies that allow us to tap informationat ever smaller concentrations and from bothcommon and rare archives. However, toreconstruct the nature, magnitude, and tim-ing of these changes, paleoclimatologistsmust also understand the biological andphysical processes that govern the formationof these diverse proxy records. As impor-tantly, the strengths and limitations of eachproxy indicator must be known and

considered for robust interpretations. Thefield of paleoclimatology is continuallybecoming more interdisciplinary as practi-tioners strive to understand and incorporatean ever increasing number of highly special-ized proxy climate and environmentalindicators.

In concert with these developments in thefield, the first two editions of ProfessorRaymond Bradley’s book, Paleoclimatology,have proven to be an indispensable resourcefor earth scientists at all stages of their careers,from undergraduate students to seasonedprofessionals. The second edition is not onlyrequired reading in my graduate paleoclima-tology course but it also occupies a prominentand easily accessible place in my researchlibrary. For almost the last three decades,Paleoclimatology has provided readers with abroad perspective on the development andinterpretation of a wide variety of climaterecords, including explanations of both estab-lished and state-of-the-art techniques used toreconstruct Quaternary climates. The text,which is accompanied by numerous illustra-tions, is sufficiently concise and instructivefor established researchers and educatorsbut is also easy for scientific novices tocomprehend.

The third edition, Paleoclimatology: Recon-structing Climates of the Quaternary, has beenextensively updated, but maintains its mis-sion of broad appeal across the various sub-disciplines of earth science. One can quicklyappreciate the comprehensive nature of thisbook by browsing through the bibliography,which contains almost 2500 references.Speaking as a long-practicing paleoclimatol-ogist, I often become immersed in the details

xv

of my specialty area and lose track of theextremely important work of colleagues inother fields that are equally essential tounderstand the larger scale processes thatconstitute our climate system. As with otherscientific fields, climatologists cannot use a“silver bullet” approach when working onand presenting their research. They mustunderstand and reference literature and datafrom other areas. The beauty of ProfessorBradley’s book is that it compiles and orga-nizes masses of both interconnected and dis-parate information (silver buckshot) in aholistic way that helps us understand thecomplexities and interdependencies in theclimate system.

This third edition is one of the best writtenreference books in the field, using prose thatis easy to understand and explanations ofdifficult concepts that are presented as onlyan experienced lecturer and teacher of Pro-fessor Bradley’s caliber can do. The text islogically arranged, beginningwith an overallreview of the reconstruction of paleoclimaterecords and a discussion of the climate sys-tem and forcing mechanisms. This is fol-lowed by a considerably detailed overviewof dating techniques, which is critical sincethe key to understanding any climatic orenvironmental record lies in robust time con-trol. Professor Bradley provides an excellentup-to-date overview of the strengths andweaknesses of the various techniques, rang-ing from classical and widely used methodssuch as radiocarbon dating to more special-ized and less “publicly” familiar methodssuch as luminescence, amino-acid, licheno-metry, and dendrochronology.

The majority of the book provides over-views of the various archives used for cli-matic and environmental reconstruction.For each of the archives, the author summa-rizes the various parameters recorded by andextracted from each type of proxy, as well ashow the time control is established, andwhat

calibration techniques are used. Abundantexamples of records derived from thesearchives are provided from aroundthe world.

In addition to revising and updating thechapters in the second edition, he expandsthe discussions of proxy records that werepreviously grouped together. Specifically,discussions on loess, speleothems, and lakesediments, which were previously groupedin a chapter called “Non-Marine GeologicalEvidence,” now appear in separate chaptersin the third edition.

In the chapter on ice cores, which is myspecialty, Professor Bradley provides acoherent and understandable primer on sta-ble isotopes in precipitation that includesinformation on their calibration for paleo-temperature reconstruction. The discussionof the records is more comprehensive thanmany other treatments of the subject, as itincludes records from both high and low lat-itudes and deals with a multitude of ice coreparameters. The longest chapter is devotedtomarine sediment records. This is appropri-ate given the huge amount of diverse litera-ture. Other chapters cover tree rings, corals,insects and biological evidence, and pollen.The final chapter covers the informationavailable from historical documentation.

I first met Professor Raymond Bradley in1983 at a NATO/NSF Workshop on AbruptClimatic Change in Biviers, France. For30 years, our paths have crossed many timesat professional meetings, seminars, andworkshops. I have also had the pleasure ofworking with him on manuscripts and bookprojects. His interests include climatology,paleoclimatology, global change, and theArctic environment. Professor Bradley is amember of the Real Climate blog and hasmade sustained and significant contribu-tions to discussions on global warming. Hehas a true passion for the paleoclimate com-munity and has worked diligently and

xvi FOREWORD

effectively on programs (such as PAGES)which strive to bring together the paleocli-mate and the modeling communities to forgea more robust understanding of global cli-mate variability in the present, past, andfuture.

We are just beginning to realize how cli-mate change has emerged as a powerfulcausal agent in the evolution of civilizations,including those that exist today. One of themajor challenges to predicting future climateis to determine the specific causes of bothpast and present changes. In light of the gen-eral conclusion of the latest Intergovernmen-tal Panel on Climate Change that “it isextremely likely that human interferencehas been the dominant cause of the observed

warming since the mid-20th century,” weurgently need to understand the natural fac-tors that forced climate variability in the past.This body of knowledge provides the criticalbaseline and corpus of knowledge that willunderpin more robust predictions of thefuture impact of human activities. ProfessorRaymond Bradley has provided the field ofpaleoclimatology an excellent spatial andtemporal summary of where we are alongthe continuum to a deeper understandingof Earth’s past and present climate.

Lonnie G. ThompsonByrd Polar Research CenterThe Ohio State University

Columbus

xviiFOREWORD

Preface to the Third Edition

The first edition of Quaternary Paleoclima-tology was published in 1985 when the fieldof paleoclimatology was still in its infancyand there was a reasonable chance that youcould read most of the relevant papers. Thefield grew rapidly over the next decade,and so I wrote a much more extensive andupdated version, Paleoclimatology: Recon-structing Climates of the Quaternary, whichwas published in 1999. Over the last decade,the field has grown even faster so that it isnow almost impossible to keep track of everyaspect of the subject. As just one example,more than 3500 papers with the keywords“ice cores” have been published since1999—a number greater than the entire fieldof paleoclimatology in the early 1980s. Inev-itably, this means that research is becomingever more specialized so that it is increas-ingly difficult to gain a broad perspectiveon the field, and to appreciate the pros andcons of particular proxies being used inpaleoclimatic reconstruction. Consequently,I think a book like this can serve an evenmore useful purpose than the first and sec-ond editions, for all those interested inunderstanding past climates. My goal fromthebeginninghasbeentoenablenonspecialistsinanyonesubfieldofpaleoclimatologyto learnenough of the basics in other subfields to allowthem to read and appreciate the literature theymight not otherwise understand. Hopefully,this will promote better communication ofideaswithin thecommunityofpaleoclimatolo-gists and beyond. As I noted in the Preface ofthe previous edition, I believe there are advan-tages in having one lens through which thisrapidly evolving field is viewed, rather thana spectrum of perspectives that an edited

volumeof specialistsmightpresent. I hope thatthose who turn to their particular areas ofexpertise will do so with the overall objectivesof the book inmind; it was simply not possibleto provide a comprehensive review of everysubfield and still try tomaintain an up-to-dateoverview of the rest of paleoclimatology. Thefinal product is thus a compromise betweencompleteness, expediency, and (eventually)exhaustion. Nevertheless, I hope I have donejustice to most topics, and that the new refer-ences I have included will enable interestedreaders to quickly access the important litera-ture.There isno substitute for reading theorig-inal scientific papers.

My goal in writing this edition was to pro-vide a comprehensive overview of the fieldof paleoclimatology and the record of cli-matic changes during the Quaternary. Newrecords are being obtained all the time, andnew analytical techniques are being devel-oped and applied, giving us new and excit-ing insights into how climates havechanged over time. I have tried to capturesome of these developments in the book.All sections have been comprehensivelyrevised and updated, but in particular, thebook includes new material on dating(including updates on calibration of theradiocarbon timescale and surface exposuredating) extensively revised chapters on icecores andmarine sediments and ocean circu-lation in the past, new chapters on loess, spe-leothems, lake sediments, and corals andgreatly revised chapters on insects, pollenanalysis, tree rings, and historical records.To keep the task somewhat manageable, Idecided not to include a separate chapteron paleoclimate models, but to keep the

xix

focus on proxies used in paleoclimaticreconstruction. Over 1200 new referenceshave been added, almost all of them pub-lished within the last decade, and there are�200 new figures, all with detailed explana-tory captions. I have learned a lot in writing

this book, and so I hope that those who readit will find it equally informative in their ownstudies.

Ray BradleyLeverett, MA, November 2013

xx PREFACE TO THE THIRD EDITION