PALEOCLIMATOLOGY. Reconstructing Climates of the Quaternary THIRD EDITION. University of Massachusetts, Amherst, Massachusetts

Transcription

1 PALEOCLIMATOLOGY Reconstructing Climates of the Quaternary THIRD EDITION RAYMOND S. BRADLEY University of Massachusetts, Amherst, Massachusetts AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Academic Press is an imprint of Elsevier

2 Contents Acknowledgments xi Front Cover Photograph xiii Foreword xv Preface to the Third Edition xix 1. Paleoclimatic Reconstruction Introduction 1 Sources of Paleoclimatic Information 4 Levels of Paleoclimatic Analysis 9 Modeling in Paleoclimatic Research Climate and Climatic Variation The Nature of Climate and Climatic Variation 13 The Climate System 16 Feedback Mechanisms 24 Energy Balance of the Earth and Its Atmosphere 27 Timescales of Climatic Variation 33 Variations of the Earth s Orbital Parameters 36 Solar Forcing 46 Volcanic Forcing Dating Methods I Introduction and Overview 55 Radioisotopic Methods 57 Radiocarbon Dating 59 Potassium-Argon Dating ( 40 K/ 40 Ar) 83 Uranium-Series Dating 85 Luminescence Dating: Principles and Applications 91 Surface Exposure Dating 98 Fission-Track Dating Dating Methods II Paleomagnetism 103 The Earth s Magnetic Field 104 Magnetization of Rocks and Sediments 105 The Paleomagnetic Timescale 107 Geomagnetic Excursions 108 Relative Paleointensity Variations 110 Secular Variations of the Earth s Magnetic Field 111 Dating Methods Involving Chemical Changes 111 Amino Acid Dating 113 Obsidian Hydration Dating 124 Tephrochronology 125 Biological Dating Methods 129 Lichenometry 129 Dendrochronology Ice Cores Introduction 137 Stable Isotope Analysis 141 Stable Isotopes in Water: Measurement and Standardization 143 Oxygen-18 Concentration in Atmospheric Precipitation 144 Factors Affecting the Stable Isotope Record in Ice Cores 145 Deuterium Excess 151 Dating Ice Cores 154 Radioisotopic Methods 155 Seasonal Variations and Episodic Events 155 Theoretical Models 165 Chronostratigraphic Correlations 167 Paleoclimatic Reconstruction from Ice Cores 167 Ice-Core Records from Greenland 167 Ice-Core Records from Antarctica 175 Past Atmospheric Composition from Polar Ice Cores 180 vii

3 viii CONTENTS Greenhouse Gas Records in Ice Cores 184 Ice-Core Records from Low Latitudes Marine Sediments Introduction 196 Paleoclimatic Information from Biological Material in Ocean Cores 197 Oxygen Isotope Studies of Calcareous Marine Fauna 199 Isotopic Composition of the Oceans 201 Oxygen Isotope Stratigraphy 211 Orbital Tuning 215 Orbital Forcing: Evidence from the Marine Record 220 Sea Level Changes and d 18 O 222 Paleotemperatures from Relative Abundance Studies 225 Paleotemperature Reconstruction from Sediment Geochemistry 228 Paleotemperatures from Alkenones 228 Paleotemperatures from TEX 86 and Long-Chain Diols 231 IP 25 and Related Sea Ice Proxies 234 Paleotemperatures from Mg/Ca Ratios 238 Oceanographic Conditions at the Last Glacial Maximum (LGM) 239 Paleoclimatic Information from Inorganic Material in Marine Sediments 244 Thermohaline Circulation of the Oceans 248 Tracers in the Ocean 252 Changes in Atmospheric Carbon Dioxide: The Role of the Oceans 258 Abrupt Climate Changes 263 Heinrich Events 267 Speleothems and Glacial Terminations 299 Millennial to Centennial Scale Changes 302 Late Glacial and Holocene Records 304 Stalagmite Records of the Last Two Millennia 310 Paleoclimatic Information from Periods of Speleothem Growth 311 Speleothems as Indicators of Sea-Level Variations Lake Sediments Sedimentology and Inorganic Geochemistry 320 Varves 323 Pollen, Macrofossils, and Phytoliths 324 Ostracods 327 Diatoms 327 Stable Isotopes 330 Organic Biomarkers Nonmarine Geologic Evidence Introduction 345 Periglacial Features 346 Snowlines and Glaciation Thresholds 351 The Climatic and Paleoclimatic Interpretation of Snowlines and ELAs 352 The Age of Former Snowlines 356 Mountain Glacier Fluctuations 358 Evidence of Glacier Fluctuations 359 The Record of Glacier Front Positions 360 Lake-level Fluctuations 362 Hydrologic Balance Models 366 Hydrologic-Energy Balance Models 370 Regional Patterns of Lake-Level Fluctuations Loess Chronology of Loess-Paleosol Sequences 284 Paleoclimatic Significance of Loess-Paleosol Sequences Speleothems Isotopic Variations in Speleothems 295 Tropical and Subtropical Paleoclimate Variability from Speleothems Insects and Other Biological Evidence from Continental Regions Introduction 377 Insects 377 Paleoclimatic Reconstructions Based on Fossil Coleoptera 379 Paleoclimatic Reconstruction Based on Aquatic Insects 384 Former Vegetation Distribution from Plant Macrofossils 388 Arctic Tree Line Fluctuations 389

4 CONTENTS ix Alpine Tree Line Fluctuations 392 Lower Tree Line Fluctuations and Rodent Middens 395 Peat Pollen Introduction 405 The Basis of Pollen Analysis 406 Pollen Grain Characteristics 408 Pollen Productivity and Dispersal: The Pollen Rain 410 Sources of Fossil Pollen 410 Preparation of the Samples 411 Pollen Analysis of a Site: The Pollen Diagram 411 Zonation of the Pollen Diagram 414 Pollen Rain as a Representation of Vegetation Composition and Climate 414 Maps of Modern Pollen Data 416 Mapping Vegetation Change: Isopolls and Isochrones 418 How Rapidly Does Vegetation Respond to Changes in Climate? 422 Quantitative Paleoclimatic Reconstructions Based on Pollen Analysis 425 Paleoclimatic Reconstruction from Long Quaternary Pollen Records 434 Europe 434 Sabana de Bogotá, Colombia 438 Central American Lowlands 441 Amazonia 443 Equatorial and Sub-Saharan Africa 445 Northeastern Siberia Tree Rings Introduction 453 Fundamentals of Dendroclimatology 454 Sample Selection 456 Cross Dating 458 Standardization of Ring-Width Data 463 Divergence 469 Calibration of Tree-Ring Data 470 Verification of Climatic Reconstructions 476 Dendroclimatic Reconstructions 480 Reconstructions of Temperatures over the Northern Hemisphere 480 Drought Reconstruction 481 Reconstruction of Atmospheric Circulation Modes 487 Wildfires and Dendroclimatology 490 Isotopic Dendroclimatology 493 d 18 O and d 2 H 493 d 13 C Corals Coral Records of Past Climate 499 Paleoclimate from Coral Growth Rates 506 Luminescence in Corals 506 d 18 O in Corals 507 d 13 C in Corals 510 D 14 C in Corals 510 Trace Elements in Corals 511 Fossil Coral Records Historical Documents Introduction 517 Historical Records and Their Interpretation 519 Historical Weather Observations 524 Historical Records of Weather-Dependent Natural Phenomena 526 Phenological and Biological Records 534 Regional Studies Based on Historical Records 538 East Asia 540 Europe 544 Records of Climate Forcing Factors 545 Climate Paradigms for the Last Millennium 548 Appendix A 553 Appendix B 557 References 559 Index 667

5 Foreword Earth is a constantly changing dynamic entity, composed of multiple complex physical, chemical, and biological systems that interact on a spectrum of time and spatial scales. To comprehend the Earth System as a whole, we must understand the nature of these complex subsystems, both now and in the past, and identify the important linkages among them. Earth is now experiencing many changes, some large and more rapid than others. To attempt predictions of how the Earth System may change in the future requires an assessment of the conditions that preceded the present, a perspective that can only be gained from the records of past climate. Studies of the past also reveal just how quickly some components of the Earth Systems have responded to specific external (e.g., solar) and internal (e.g., atmospheric chemistry) forcing factors. Knowledge of these changes and understanding their key drivers are critical to efforts to anticipate and plan for future environmental changes. We are very fortunate that today we have a rich body of knowledge and numerous diverse natural systems that record many types of climatic and environmental information across a spectrum of temporal scales. Additionally, we now have rich array of technologies that allow us to tap information at ever smaller concentrations and from both common and rare archives. However, to reconstruct the nature, magnitude, and timing of these changes, paleoclimatologists must also understand the biological and physical processes that govern the formation of these diverse proxy records. As importantly, the strengths and limitations of each proxy indicator must be known and considered for robust interpretations. The field of paleoclimatology is continually becoming more interdisciplinary as practitioners strive to understand and incorporate an ever increasing number of highly specialized proxy climate and environmental indicators. In concert with these developments in the field, the first two editions of Professor Raymond Bradley s book, Paleoclimatology, have proven to be an indispensable resource for earth scientists at all stages of their careers, from undergraduate students to seasoned professionals. The second edition is not only required reading in my graduate paleoclimatology course but it also occupies a prominent and easily accessible place in my research library. For almost the last three decades, Paleoclimatology has provided readers with a broad perspective on the development and interpretation of a wide variety of climate records, including explanations of both established and state-of-the-art techniques used to reconstruct Quaternary climates. The text, which is accompanied by numerous illustrations, is sufficiently concise and instructive for established researchers and educators but is also easy for scientific novices to comprehend. The third edition, Paleoclimatology: Reconstructing Climates of the Quaternary, has been extensively updated, but maintains its mission of broad appeal across the various subdisciplines of earth science. One can quickly appreciate the comprehensive nature of this book by browsing through the bibliography, which contains almost 2500 references. Speaking as a long-practicing paleoclimatologist, I often become immersed in the details xv

6 xvi FOREWORD of my specialty area and lose track of the extremely important work of colleagues in other fields that are equally essential to understand the larger scale processes that constitute our climate system. As with other scientific fields, climatologists cannot use a silver bullet approach when working on and presenting their research. They must understand and reference literature and data from other areas. The beauty of Professor Bradley s book is that it compiles and organizes masses of both interconnected and disparate information (silver buckshot) in a holistic way that helps us understand the complexities and interdependencies in the climate system. This third edition is one of the best written reference books in the field, using prose that is easy to understand and explanations of difficult concepts that are presented as only an experienced lecturer and teacher of Professor Bradley s caliber can do. The text is logically arranged, beginning with an overall review of the reconstruction of paleoclimate records and a discussion of the climate system and forcing mechanisms. This is followed by a considerably detailed overview of dating techniques, which is critical since the key to understanding any climatic or environmental record lies in robust time control. Professor Bradley provides an excellent up-to-date overview of the strengths and weaknesses of the various techniques, ranging from classical and widely used methods such as radiocarbon dating to more specialized and less publicly familiar methods such as luminescence, amino-acid, lichenometry, and dendrochronology. The majority of the book provides overviews of the various archives used for climatic and environmental reconstruction. For each of the archives, the author summarizes the various parameters recorded by and extracted from each type of proxy, as well as how the time control is established, and what calibration techniques are used. Abundant examples of records derived from these archives are provided from around the world. In addition to revising and updating the chapters in the second edition, he expands the discussions of proxy records that were previously grouped together. Specifically, discussions on loess, speleothems, and lake sediments, which were previously grouped in a chapter called Non-Marine Geological Evidence, now appear in separate chapters in the third edition. In the chapter on ice cores, which is my specialty, Professor Bradley provides a coherent and understandable primer on stable isotopes in precipitation that includes information on their calibration for paleotemperature reconstruction. The discussion of the records is more comprehensive than many other treatments of the subject, as it includes records from both high and low latitudes and deals with a multitude of ice core parameters. The longest chapter is devoted to marine sediment records. This is appropriate given the huge amount of diverse literature. Other chapters cover tree rings, corals, insects and biological evidence, and pollen. The final chapter covers the information available from historical documentation. I first met Professor Raymond Bradley in 1983 at a NATO/NSF Workshop on Abrupt Climatic Change in Biviers, France. For 30 years, our paths have crossed many times at professional meetings, seminars, and workshops. I have also had the pleasure of working with him on manuscripts and book projects. His interests include climatology, paleoclimatology, global change, and the Arctic environment. Professor Bradley is a member of the Real Climate blog and has made sustained and significant contributions to discussions on global warming. He has a true passion for the paleoclimate community and has worked diligently and

7 FOREWORD xvii effectively on programs (such as PAGES) which strive to bring together the paleoclimate and the modeling communities to forge a more robust understanding of global climate variability in the present, past, and future. We are just beginning to realize how climate change has emerged as a powerful causal agent in the evolution of civilizations, including those that exist today. One of the major challenges to predicting future climate is to determine the specific causes of both past and present changes. In light of the general conclusion of the latest Intergovernmental Panel on Climate Change that it is extremely likely that human interference has been the dominant cause of the observed warming since the mid-20th century, we urgently need to understand the natural factors that forced climate variability in the past. This body of knowledge provides the critical baseline and corpus of knowledge that will underpin more robust predictions of the future impact of human activities. Professor Raymond Bradley has provided the field of paleoclimatology an excellent spatial and temporal summary of where we are along the continuum to a deeper understanding of Earth s past and present climate. Lonnie G. Thompson Byrd Polar Research Center The Ohio State University Columbus

8 Preface to the Third Edition The first edition of Quaternary Paleoclimatology was published in 1985 when the field of paleoclimatology was still in its infancy and there was a reasonable chance that you could read most of the relevant papers. The field grew rapidly over the next decade, and so I wrote a much more extensive and updated version, Paleoclimatology: Reconstructing Climates of the Quaternary, which was published in Over the last decade, the field has grown even faster so that it is now almost impossible to keep track of every aspect of the subject. As just one example, more than 3500 papers with the keywords ice cores have been published since 1999 a number greater than the entire field of paleoclimatology in the early 1980s. Inevitably, this means that research is becoming ever more specialized so that it is increasingly difficult to gain a broad perspective on the field, and to appreciate the pros and cons of particular proxies being used in paleoclimatic reconstruction. Consequently, I think a book like this can serve an even more useful purpose than the first and second editions, for all those interested in understanding past climates. My goal from the beginning has been to enable nonspecialists in any one subfield of paleoclimatology to learn enough of the basics in other subfields to allow them to read and appreciate the literature they might not otherwise understand. Hopefully, this will promote better communication of ideas within the community of paleoclimatologists and beyond. As I noted in the Preface of thepreviousedition,ibelievethereareadvantages in having one lens through which this rapidly evolving field is viewed, rather than a spectrum of perspectives that an edited volume of specialists might present. I hope that those who turn to their particular areas of expertise will do so with the overall objectives of the book in mind; it was simply not possible to provide a comprehensive review of every subfield and still try to maintain an up-to-date overview of the rest of paleoclimatology. The final product is thus a compromise between completeness, expediency, and (eventually) exhaustion. Nevertheless, I hope I have done justice to most topics, and that the new references I have included will enable interested readers to quickly access the important literature. There is no substitute for reading the original scientific papers. My goal in writing this edition was to provide a comprehensive overview of the field of paleoclimatology and the record of climatic changes during the Quaternary. New records are being obtained all the time, and new analytical techniques are being developed and applied, giving us new and exciting insights into how climates have changed over time. I have tried to capture some of these developments in the book. All sections have been comprehensively revised and updated, but in particular, the book includes new material on dating (including updates on calibration of the radiocarbon timescale and surface exposure dating) extensively revised chapters on ice cores and marine sediments and ocean circulation in the past, new chapters on loess, speleothems, lake sediments, and corals and greatly revised chapters on insects, pollen analysis, tree rings, and historical records. To keep the task somewhat manageable, I decided not to include a separate chapter on paleoclimate models, but to keep the xix

9 xx PREFACE TO THE THIRD EDITION focus on proxies used in paleoclimatic reconstruction. Over 1200 new references have been added, almost all of them published within the last decade, and there are 200 new figures, all with detailed explanatory captions. I have learned a lot in writing this book, and so I hope that those who read it will find it equally informative in their own studies. Ray Bradley Leverett, MA, November 2013