Quaternary Environmental Change in the Tropics

Sarah Metcalfe is Professor of Earth and Environmental Dynamics at the University of Nottingham, UK. She has published extensively on environmental change in Latin America, with a particular focus on Mexico. Although primarily a palaeolimnologist, her approach is very much multi-proxy, including the use of historical and instrumental records to help to improve our understanding of recent change. David Nash is Professor of Physical Geography at the University of Brighton, UK. He is widely known for his publications on the reconstruction of historical climate changes in southern Africa, as well as his broader research into the contemporary and Quaternary geomorphology of dryland regions including the Kalahari, Atacama and southern Europe. His research uses methods ranging from scanning electron microscopy and thin-section analysis to the interpretation of historical documents.

List of contributors, xi Preface, xiii Acknowledgements, xiv I Global contexts, 1 1 Introduction, 3 Sarah E. Metcalfe and David J. Nash 1.1 Why the tropics matter, 3 1.1.1 Defining the tropics, 3 1.1.2 Importance of the tropics, 4 1.2 Development of ideas, 8 1.2.1 Early ideas about tropical environmental change, 8 1.2.2 The twentieth century revolution, 9 1.2.3 Advances in modelling, 12 1.3 Establishment of the tropical climate system, 13 1.4 Drivers of tropical environmental change, 17 1.5 The tropics as drivers of change, 20 1.5.1 The tropics and greenhouse gas concentrations, 20 1.5.2 Impacts of low latitude volcanic eruptions, 22 1.5.3 Dust emissions from the tropics and subtropics, 23 1.6 Extra-tropical forcing, 24 1.7 Organisation of the volume, 24 Acknowledgements, 25 References, 25 2 Contemporary climate and circulation of the tropics, 34 Stefan Hastenrath 2.1 Introduction, 34 2.2 Diurnal and local processes, 34 2.3 Planetary context, 35 2.4 Regional circulation systems, 36 2.4.1 Jet streams, 36 2.4.2 Subtropical highs and trade winds, 37 2.4.3 Equatorial trough zone, 37 2.4.4 Monsoons, 38 2.4.5 Equatorial zonal circulations, 38 2.5 Climatic variability, 39 2.5.1 Southern Oscillation and El Nino, 39 2.5.2 Indian Monsoon, 40 2.5.3 Northeast Brazil, 41 2.5.4 Sahel, 41 2.5.5 Timescales of variability, 42 2.6 Concluding remarks, 42 References, 42 II Regional environmental change, 45 3 Tropical oceans, 47 Jan-Berend W. Stuut, Matthias Prange, Ute Merkel and Silke Steph 3.1 Tropical oceans in the global climate system, 47 3.1.1 Modern climatology, 47 3.1.2 El Nino Southern Oscillation and its relatives, 50 3.1.3 Solar and volcanic radiative forcing of tropical oceans, 51 3.1.4 Tropical oceans and monsoons, 53 3.1.5 The tropical oceans as part of the global conveyor belt, 53 3.2 Reconstructing past ocean conditions, 55 3.2.1 Proxies for SST and SSS, 55 3.2.2 Reconstructing continental climate using marine archives, 57 3.3 Tropical oceans throughout the Quaternary, 57 3.3.1 Glacial interglacial cycles, 57 3.3.2 Early Quaternary (the 41-kyr world ), 57 3.3.3 Mid-Pleistocene Transition, 58 3.3.4 Late Quaternary (the 100-kyr world ), 60 3.4 The past 20 000 years, 60 3.4.1 The Last Glacial Maximum, 60 3.4.2 Glacial termination: an active role for the tropics?, 61 3.4.3 History of the equatorial Pacific and the state of ENSO, 65 3.4.4 The Holocene, 66 3.5 Outlook, 68 References, 69 4 Africa, 79 David J. Nash and Michael E. Meadows 4.1 Introduction, 79 4.2 Potential climate forcing factors, 85 4.3 Mediterranean North Africa, 88 4.3.1 Contemporary climate and sources of palaeoenvironmental information, 88 4.3.2 Longer records, 88 4.3.3 The Last Glacial Maximum, 89 4.3.4 The last glacial interglacial transition, 92 4.3.5 The Holocene, 93 4.4 The Sahara and the Sahel, 94 4.4.1 Contemporary climate and sources of palaeoenvironmental information, 94 4.4.2 Longer records, 95 4.4.3 The Last Glacial Maximum, 96 4.4.4 The last glacial interglacial transition, 97 4.4.5 The Holocene, 99 4.5 Equatorial Africa, 103 4.5.1 Contemporary climate and sources of palaeoenvironmental information, 103 4.5.2 Longer records, 104 4.5.3 The Last Glacial Maximum, 107 4.5.4 The last glacial interglacial transition, 109 4.5.5 The Holocene, 110 4.6 Southern Africa, 113 4.6.1 Contemporary climate and sources of palaeoenvironmental information, 113 4.6.2 Longer records, 113 4.6.3 The Last Glacial Maximum, 118 4.6.4 The last glacial interglacial transition, 121 4.6.5 The Holocene, 122 4.7 Synthesis, 127 4.8 Directions for future research, 129 References, 129 5 India, Arabia and adjacent regions, 151 Ashok K. Singhvi, Nilesh Bhatt, Ken W. Glennie and Pradeep Srivastava 5.1 Introduction, 151 5.2 Quaternary of India and Tibet, 153 5.2.1 Arid and semi-arid regions, 154 5.2.2 Aeolian sands, 154 5.2.3 Aeolian dust (loess deposits), 159 5.2.4 Volcanic ash, 159 5.2.5 Lacustrine records, 161 5.2.6 Peat deposits, 166 5.2.7 Calcretes, 167 5.2.8 Coastal records, 167 5.2.9 Fluvial records, 171 5.2.10 Cave deposits, 176 5.3 Quaternary of the Arabian Sea and Bay of Bengal, 176 5.4 Quaternary of Arabia and the Middle East, 177 5.4.1 Fluvial (wadi) systems, 179 5.4.2 Lacustrine (and sabkha) records, 180 5.4.3 Cave deposits, 182 5.4.4 Aeolian sands, 183 5.4.5 Gypsum in dunes, 187 5.4.6 Late Quaternary Persian (Arabian) Gulf, 188 5.4.7 Dating aeolian sediment supply, 189 5.4.8 Climatic optimum and modern Arabian civilisation, 191 5.4.9 Summary of environmental changes in Arabia and the Middle East, 191 5.5 Conclusions, 192 Acknowledgements, 196 References, 196 6 China and Southeast Asia, 207 Dan Penny 6.1 The South and Southeast Asian region as a component of the Earth system, 207 6.2 Setting the stage for the Quaternary: environmental context and controls, 211 6.3 Regional syntheses, 214 6.3.1 China, 214 6.3.2 Indochina, 221 6.3.3 Sundaland and Wallacea, 225 6.4 The Asian tropics during the Quaternary: driver of planetary change?, 229 References, 230 7 Australia and the southwest Pacific, 236 Peter Kershaw and Sander van der Kaars 7.1 Introduction, 236 7.2 Northeastern Australia, 240 7.2.1 Orbital timescale, 240 7.2.2 Suborbital timescale, 244 7.2.3 Termination 1 and the Holocene, 244 7.3 Northern Australia, 245 7.3.1 Orbital timescale, 245 7.3.2 Termination 1 and the Holocene, 246 7.4 Northwestern Australia, 247 7.4.1 Orbital timescale, 247 7.4.2 Termination 1 and the Holocene, 249 7.5 Western Australia, 249 7.5.1 Orbital timescale, 249 7.5.2 Termination 1 and the Holocene, 251 7.6 Central Australia, 251 7.6.1 Orbital timescale, 251 7.6.2 Termination 1 and the Holocene, 253 7.7 Southwest Pacific Islands, 253 7.8 General discussion and conclusions, 254 7.8.1 Early Quaternary, 254 7.8.2 Late Quaternary cyclicity and abrupt events, 255 7.8.3 Late Quaternary climate alterations, 256 Acknowledgements, 258 References, 258 8 Latin America and the Caribbean, 263 Mark B. Bush and Sarah E. Metcalfe 8.1 Introduction, 263 8.2 Precursor to the Quaternary, 264 8.2.1 Climatic consequences of closure of the Isthmus of Panama, 267 8.2.2 Biotic consequences of closure of the Isthmus of Panama, 267 8.3 Climate mechanisms, 267 8.3.1 Modern climatology, 267 8.3.2 The forcing of Neotropical climates, 270 8.4 Long term climate forcings and cycles, 271 8.4.1 Eccentricity, 271 8.4.2 Precessional cycles and precipitation patterns, 272 8.4.3 Precession as a mixed signal, 273 8.5 Records of climate change, 274 8.5.1 Glacial advance and the LGM, 274 8.5.2 Glacial cooling, 276 8.5.3 Glacial-age precipitation, 278 8.5.4 The status of the refugial hypothesis of tropical diversity, 284 8.5.5 The last deglaciation, 286 8.5.6 The early-mid Holocene, 287 8.5.7 Late Holocene oscillations, 289 8.6 Other climate forcings, 289 8.6.1 Millennial-scale oscillations, 289 8.6.2 Solar cycles, 291 8.6.3 El Nino Southern Oscillation, 292 8.7 El Nino records, 292 8.7.1 Archaeology, 292 8.7.2 Historical records, 293 8.7.3 Tree ring records, 293 8.7.4 Corals, 294 8.7.5 Sedimentary records, 295 8.8 Climate and societies, 296 8.8.1 Early agriculture, 296 8.8.2 Cultural collapse, 297 8.9 Conclusions, 298 Acknowledgements, 301 References, 301 III Global syntheses, 313 9 Modelling of tropical environments during the Quaternary, 315 Zhengyu Liu and Pascale Braconnot 9.1 Introduction, 315 9.2 Tropical climate in the Holocene: response to orbital forcing, 316 9.2.1 Orbital forcing, 316 9.2.2 Monsoon response, 317 9.2.3 SST response and oceanic feedback, 319 9.2.4 Precession forcing and obliquity forcing, 324 9.2.5 Ecosystem response and feedback, 330 9.3 Tropical climate at the LGM: the roles of GHGs and ice sheet forcing, 333 9.3.1 Greenhouse gases and ice sheet forcing, 333 9.3.2 Temperature response and climate sensitivity, 333 9.3.3 Monsoon and hydrological response, 338 9.3.4 Ecosystem response and feedbacks, 339 9.4 Tropical climate variability, 339 9.4.1 ENSO and ocean atmosphere interaction, 340 9.4.2 Abrupt change of monsoon climate, 343 9.4.3 Tropical variability and its interaction with high-latitude variability, 344 9.5 Summary and further discussion, 349 9.5.1 Summary, 349 9.5.2 Other issues in Quaternary tropical climate modelling, 350 9.5.3 Climate models of intermediate complexity, 350 9.5.4 Perspective of Earth system modelling of past climate, 351 References, 352 10 Historical environmental change in the tropics, 360 Georgina H. Endfi eld and Robert B. Marks 10.1 Introduction, 360 10.2 Climate change and society in the tropics in the last 1000 years, 361 10.2.1 Climate variability and harvest history in China, 365 10.2.2 Climate and crisis in colonial Mexico, 370 10.3 Exploring anthropogenic impacts in the tropics, 375 10.3.1 Deforesting China, 378 10.3.2 Exploring pre- and post-conquest land use changes in central Mexico, 380 10.4 Recent and future environmental changes in the vulnerable tropics, 382 References, 384 11 Past environmental changes, future environmental challenges, 392 David J. Nash and Sarah E. Metcalfe 11.1 Patterns of tropical environmental change, 392 11.1.1 Last Interglacial, 392 11.1.2 Last Glacial Maximum, 394 11.1.3 The last deglaciation or last glacial interglacial transition, 396 11.1.4 The Holocene, 398 11.2 Forcings, 401 11.3 Future change in the tropics, 402 11.3.1 Climate responses, 402 11.3.2 Water resources, 404 11.3.3 Biodiversity, 406 11.4 The tropics as drivers of change, 406 11.5 Conclusions, 408 References, 409 Index, 412 Colour plate pages fall between pp. 210 and 211