A 200-year sediment record of environmental change from Lake Sayram, Tianshan Mountains in China

Abstract

Two parallel sediment cores (30 cm long) were extracted from Lake Sayram, in the Tianshan Mountains of Xinjiang in arid northwest China. We used ²¹⁰Pb and ¹³⁷Cs dating, multi-proxy indices, including geochemical composition, carbonate content, magnetic susceptibility (MS), and δ¹³C and δ¹⁸O of bulk carbonate, to reconstruct regional environmental change over the past two centuries. High evaporation modifies δ¹⁸O and δ¹³C of the dissolved inorganic carbon in lake water and may be responsible for the covariance between δ¹³C and δ¹⁸O of bulk carbonate. The ratio of immobile to mobile elements (CI = (Fe+Al+Mn+Cr+Co+Ni)/(K+Na+Ca+Mg+Sr+Ba)) is associated with humidity, and the ratio of Sr/Ca reflects lake salinity. Constrained cluster analysis of the multi-proxy indices was used to partition sediment deposition into three periods. In the first period of 1820–1890s, the climate was dryer with high evaporation, and lake water had higher salinity. During the second period from 1890s to 1960s, multi-proxy indices suggested that regional humidity increased and there was relatively more chemical weathering. The latest period, 1960s to present day, was the wettest of the past nearly 200 years. Nevertheless, we infer that human-related impacts have greatly increased in the last 50 years from the increased MS and phosphorus content.

Keywords::

• Lake Sayram
• lake sediment
• multi-proxy indices
• environmental change

Acknowledgements

The authors thank Longsheng Xu and Yuxing Zhu for field and laboratory assistance. Thanks are also due to Mark Johnson for his helpful comments and revision of the text and the reviewers for their helpful comments and suggestions that improved the manuscript. This study was supported by National Natural Science Foundation of China (U1138301; 41101190) and National Basic Research Program of China (2012CB956102), West Doctor Project of Chinese Academy of Sciences (XBBS201106).