CLIMATIC AND ENVIRONMENTAL SIGNIFICANCE OF OSTRACOD ABUNDANCE AND THEIR SHELL OXYGEN ISOTOPE FROM LAKE QINGHAI SURFACE SEDIMENTS

Ostracods have been widely used in the lacustrine palaeoenvironment reconstruction. Multi-proxies, including ostracod abundance (TA_OST, TA_Li and TA_Em), ostracod shell oxygen isotope (δ¹⁸O_OST), total inorganic carbonate content (TIC) and its oxygen isotope (δ¹⁸O_TIC) are examined for a short core from the southeastern basin of Lake Qinghai. Together with the former researches, the result shows that in the past~560 a there were only two species, Limnocythere inopinata and Eucypris mareotica,survived in the lake. Their abundance indicates the changes in salinity. There exists a systematic difference between δ¹⁸O_OST and δ¹⁸O_TIC, with the latter more negative, probably due to their difference in formation time (seasonal difference), water depth and/or microenvironment. Furthermore,in some sections the δ¹⁸O_OST changes earlier than δ¹⁸O_TIC. All the proxies show a covariance trend, responding to the changes in water salinity and partly in the effective humidity of the lake area. Based on these proxies, five dry-wet phases are reconstructed for the past~560a in Lake Qinghai. It should be noticed that the discussion and results are just limited to one sediment core in the southeastern basin of Lake Qinghai. The environmental significance of these proxies and their relationship need further systematic researches spatially and temporally.