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《中国科学:地球科学(英文版)》 2016-05
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A 12-kyr record of microbial branched and isoprenoid tetraether index in Lake Qinghai, northeastern Qinghai-Tibet Plateau: Implications for paleoclimate reconstruction

WANG HuanYe;DONG HaiLiang;ZHANG ChuanLun;JIANG HongChen;LIU WeiGuo;State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences;College of Earth Sciences, University of Chinese Academy of Sciences;State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences;State Key Laboratory of Marine Geology, Tongji University;  
Branched and Isoprenoid Tetraether(BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers(b GDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of b GDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake(Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas b GDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake.
【Fund】: supported by the Major State Basic Research Development Program of China (Grant No. 2013CB955900);; the National Natural Science Foundation of China (Grant Nos. 41373022 41573005)
【CateGory Index】: P532;P593
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