Environmental magnetic studies of sediment cores f

Authors: Fahu Chen Jianbao Liu Qinghai Xu Yuecong Li Jianhui Chen Haitao Wei Qingsong Liu Zongli Wang Xianyong Cao Shengrui Zhang

Publish Date: 2013/02/27

Volume: 49, Issue: 3, Pages: 447-464

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Abstract

Environmental magnetic studies were conducted on a 942mlong sediment core from Gonghai Lake North China Radiocarbon dating indicates that the record spans the last 15000 cal year BP The principal magnetic mineral in the sediments is pseudosingle domain magnetite of detrital origin with minimal postdepositional alteration Although the variations in the concentration of detrital magnetic minerals and their grain size throughout the core reflect inputs from both soil erosion and eolian dust it is shown that their climatic and environmental significance changes with time In the lowermost part of the core ~15000–11500 cal year BP the magnetic minerals were supplied mainly by bedrock erosion soil erosion and dust input when climate ameliorated after the cold and dusty last glacial maximum The increasing magnetic susceptibility χ in this interval may indicate a combination of changes in the lake environment together with catchmentsurface stabilization and a decreasing proportion of dust input In the central part of the core ~11500–1000 cal year BP the detrital magnetic minerals mainly originated from dust inputs from outside the catchment when the lake catchment was covered by forest and catchmentderived sediment supply and thus the lake sediment accumulation rate were minimal The generally low concentration of magnetic minerals in this part of the core reflects the highest degree of soil stability and the strongest summer monsoon during the Holocene In the uppermost part of the core the last ~1000 years detrital magnetic minerals mainly originated from erosion of catchment soils when the vegetation cover was sparse and the sediment accumulation rates were high Within this part of the core the high magnetic susceptibility reflects strong pedogenesis in the lake catchment and thus a strong summer monsoon This scenario is similar to that recorded in loess profiles Overall the results document three main stages of summer monsoon history with abrupt shifts from one stage to another an increasing and variable summer monsoon during the last deglacial a generally strong summer monsoon in the early and middle Holocene and a weak summer monsoon in the late Holocene The results also suggest that different interpretational models may need to be applied to lake sediment magnetic mineral assemblages corresponding to different stages of environmental evolutionWe sincerely thank the following Mr Youliang Su and Mr Zhaoxia Jiang for their help with the laboratory analyses Dr Jan Bloemendal for substantially improving the English and the anonymous reviewers and the editor for their constructive suggestions and comments This work was supported by the National Basic Research Program of China 2010CB950202 the National Natural Science Foundation of China 40971056 41130102 and 41025013 and the 111 Project B06026 Special thanks should be given to Prof Rick Battarbee who has done much to enhance the study of paleolimnology at Lanzhou University through training provided in the UK and China as part of a British Council Higher Education Link Programme between University College London and Lanzhou University from 1999 to 2003

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