Holocene Climate Change Documented By Ostracod Species Assemblages And Carbon Oxygen Isotopes Of Boten Lake, Xinjiang, China

Bosten Lake, the largest inland freshwater lake in China, is strongly influenced by westerly and the climatic changes during the Holocene could be preserved in the lake sediments. In order to understand the processes and the patterns of the Holocene climate in this region, we carried out systemtaic analyses on lake sediments from BST04H core. Based on the age model established by means of ²¹⁰Pb,¹³⁷Cs and AMS¹⁴C dating, we reconstructed the regional climate and the lake status since early Holocene besed on comprehensive analyses of abundance of ostracods, percentage of species, freshwater species, near-shore species, and stable-isotopes of ostracod shells. Our results have also been compared with others cores in Bosten Lake by previous researches. The primary conclusions are as follows:1. The abundance of ostracod shells indicates adaptability of the host water for ostracod species. Freshwater species indicates freshwater input and lake level increase. Litorial species indicates decreased water depth and lake level drop. Oxygen isotopes of ostracod shells vary between -4.29‰and 6.88‰,over a range of 10‰,which could not be attributed to water temperature variations or species differences. This large d¹⁸O amplitude suggests that it is mainly a reflection of the isotopic composition of the host water, which is controlled by the precipitation (water input)/evaporation ratios.2. Bosten Lake expereicenced several stages during the Holocence based on the ostracod species assemblages and the stable-isotopes analyses. From 9620-7420cal yr B.P.,the lake expanded and water depth increased; During the period 7420⁶100 cal yr B.P., the lake was in a stady state, but the lake level was droping slowly; From 6100-5130 cal yr B.P., the lake level fluctuated freqently with small amplitudes;A relatively stable period appeared during 3750-1130 cal yr B.P.; The lake expanded again and tended to a steady state during late Holocene from 1130-490 cal yr B.P.; The most recent period from 490-101 cal yr B.P., the lake returned to a steady state after a short period of extraction.3. There is consistency in the records from Bosten Lake between our BST04H core and other cores, but differences are also identified. These differences may be due to differences in sampling locations, sample resolution, age models and the proxy indicators.