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C:\Documents and Settings\lproctor\Local Settings\Temporary Internet Files\OLK8\Copyright - thesis (2).doc Late Holocene environmental change on the NE Tibetan Plateau: a palaeolimnological study of Lake Qinghai and Lake Gahai, China, based on stable isotopes Thesis submitted for the degree of Doctor of Philosophy University College London ANDREW CHARLES GRAHAM HENDERSON Department of Geography University College London July 2004 1 UMI Number: U592894 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U592894 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Abstract Climate driven hydrologic variability has direct socio-economic impacts on local, regional and global scales. Particularly vulnerable is the region that lies within the boundaries of the East Asian monsoon, which is one of the most pronounced and influential phenomena of Earth’s climate system. People within the heavily populated Asian countries have adapted many aspects of their society to the subtleties of monsoon rains, and are thus highly susceptible to small changes in the timing and intensity of monsoon precipitation. This study aims to reconstruct high-resolution late Holocene climatic and hydrologic variability from Lake Qinghai, NE Tibetan Plateau, using stable isotope techniques. The thesis also examines the modern isotope systematics of Lake Qinghai through mass balance methods to understand the modern hydrology of the lake in order to determine which factors are important in influencing lake water isotope composition. The isotopic compositions of Lake Qinghai’s modern waters indicate that they have been modified by evaporation, as they plot below the Global Meteoric Water Line (GMWL). Isotope mass balance models quantify this, and demonstrate that 29 to 35% of the waters entering the lake are from direct precipitation and surface runoff, while evaporation from the lake’s surface accounts for 44 to 54% of the lakes water loss. This suggests that the balance of precipitation to evaporation (P/E) is an important control on the composition of lake waters and therefore carbonate incorporated into the sediment record will reflect this. Four cores were used in this study and they provide a palaeohydrological history displaying distinct changes in 518Oauth and 513Cauth over the past 1500 years. These are interpreted in terms of effective moisture and one particularly pronounced event, between 1600 and 1850 AD has been attributed to decreases in evaporation. This event, when compared to other regional palaeoenvironmental archives is coincident with cold temperatures, synonymous with the Northern Hemisphere Little Ice Age, tentatively suggested to be a result of solar variability. 2 Acknowledgements I thank my principal supervisor, Dr. Jonathan Holmes, for his encouragement, motivation, and scientific input, particularly the finer points of isotope geochemistry and for covering teaching duties when not in the country. I would also like to thank Dr. Melanie Leng as her encouragement and gentle prodding has been invaluable throughout the completion of this research. Additionally, I am indebted to Prof. Rick Battarbee who sparked my fascination in the wonders of Lake Qinghai and for his continuing enthusiasm for the subject! This PhD would have not been possible without the support of a Department of Geography Teaching Assistantship, which I gratefully acknowledge. Funding for fieldwork and analytical work was generously provided by a host of sources: Department of Geography, UCL Graduate School, The British Council, the ENSIS Trust Fund, the Environmental Change Research Centre, the NERC Isotope Geosciences Laboratory, the NERC Radiocarbon Laboratory, the Royal Society Dudley Stamp Memorial Fund, and Dr. Anson Mackay. While overseas I have been lucky enough to meet and work with a number of people, many of whom I now call friends and their hospitality and generosity helped make my trips to China so enjoyable. In particular, I would like to thank Prof. Fahu Chen, Dr. Jiawu Zhang, Jin Ming, Jinbao Li, Xiahou Guo, Jijun Li, Yan Zhao and Chengjun Zhang. They acted as fabulous hosts and many worked with me in the field acting as translators, logistical support and explained the finer points of Chinese drinking games. Other ‘support’ in the field came in the form of Tom ‘no trousers’ Davidson who despite all attempts to wreck a well-oiled machine proved invaluable help. My thanks go to the people who put me on the right tracks in the laboratory. Namely, Melanie Leng, Carol Arrowsmith, and Hilary Sloane at NIGL, Keyworth, Andy Cundy at the University of Sussex, Charlotte Bryant at the NERC-RCL, East Kilbride and Ian Slipper at the University of Greenwich. I would also like to thank Dr. Tim Jull for analysis of modern water for radiocarbon, Prof. Lonnie Thompson for providing the Dunde ice core data, Dr. Achim Brauning for supplying the temperature composite series and Dr. Hong Chun Li for providing me with the Buddha cave dataset. I am eternally grateful to my friends at UCL, especially to; Gina Clarke, Sally Luckes, Sam Mendelson, Carl Sayer, Ben Goldsmith, Tom Davidson, Martin Kernan, Patrick Rioual, Helen Bennion, Kira Larsen, David Morley and all the others, for their generosity of spirit and for knowing that if all else fails, there is always the Lord John Russell. Finally, I would like to thank my family and friends at home, who continue to support me despite my nuances and I dedicate this thesis to my Dad, Martyn John Henderson. 3 Table of contents Title page 1 Abstract 2 Acknowledgements 3 Table of contents 4 List of figures 7 List of tables 11 1. Chapter One - Introduction ____________________________________________________________ 1.1 Research aims 12 1.2 Thesis structure 15 2. Chapter Two - Using stable isotopes to reconstruct past climate 2.1 Lakes 16 2.1.1 Closed-basins - saline lakes 17 2.2 Controls on isotopes in precipitation 18 2.3 Controls on isotopes in lake water 20 2.3.1 Isotope steady-state 21 2.4 Controls on stable isotopes in lake sediments 22 2.4.1 Authigenic carbonate 22 2.4.2 Biogenic carbonate 24 2.5 Indirect controls on oxygen isotope composition 24 2.5.1 pH 24 2.5.2 Mineralogy 26 2.6 Controls on carbon isotopes in lake sediments 26 2.7 Isotope covariance 28 2.8 Organic carbon 29 2.9 Summary 29 3. Chapter Three - The environmental history of NW China and the Tibetan Plateau 3.1 Uplift of the Tibetan Plateau 31 3.2 The climate of China 32 3.3 Climatic history of NW China and the Tibetan Plateau 36 3.3.1 Glacial-Holocene transition 37 3.3.2 The Holocene optimum 40 3.3.3 Last millennium 42 3.4 Lake Qinghai 49 3.4.1 Geological setting and catchment characteristics 49 3.4.2 Hydrological setting of Lake Qinghai 49 3.4.3 Catchment geomorphology and environmental history 54 3.5 Previous records of environmental change from Lake Qinghai 55 4 3.6 Summary 58 Chapter Four - - Methods 4.1 Methodology for water analysis 61 4.1.1 Collection of modern waters 61 4.1.2 Physical limnology 62 4.1.3 Isotopic analysis of modern waters 64 4.1.3.1 Oxygen isotope analysis and hydrogen isotope analysis 64 4.1.3.2 Carbon isotope analysis 64 4.2 Methods for sediment analysis 64 4.2.1 Collection of surface sediments and core sediments 64 4.2.1.1