Climate And Environment Changes Recorded By Sediments From Bangong Co In Tibet Since Last Deglaciation

Asian summer monsoon is an important component of atmospheric circulation. It is of great significance to study the monsoon evolution history and its driving mechanisms.This study focuses on multi-proxy records, including ostracod assemblages, carbonate isotopes, grain size, and carbonate content, from Bangong Co in northwest Tibet to provide a paleoclimatic and paleoenviromental record for this region. 15 bulk organic matter samples and 4 plant remains samples were used to date the core with using AMS 14 C dating method. The chronology was then established after evaluating the radiocarbon reservoir effect. Modern investigations provide environmental significance for the proxies. The result indicates both the variation of grain size and ostracod species could represent the lake level fluctuations. Carbonate oxygen isotope reflects the composition of lake water isotope(δ18Ow)which was dominated by the δ18O of precipitation and lake hydrology.The regional lake evolution history can be divided into three stages since last deglacial indicated by the proxies of the core BGC-2011. The last deglacial(14.3~11.5 cal ka BP) was characterized by a low lake level and high salinity indicated by the ostracod assemblages, carbonate content, coarse grain size and δ18Ocarb. During the early Holocene(11.5~7.8 cal ka BP), all the proxies suggested that the lake water desalted, lake area expanded, the core site was in deep and stable environment due to the opening of the lake system. Bangong Co experienced high temperature and high productivity during 7.8~6.4 cal ka BP, resulting in inverse correlation between carbonate oxygen isotope and carbonate carbon isotope, while low temperature of lake water prevailed after 6.4 cal ka BP. In the late Holocene(3.4 cal ka BP~now), lake level dropped and the coring site was under shallow water condition, suggest a dry climate. Fresh water ostracod species disappeared and δ18Ocarb increased after 0.8 cal ka BP, likely correlated with enclosure of the lake basin.Regional comparison of δ18Ocarb from Bangong Co with those from other Tibetan lakes and Asian summer monsoon records indicated that northern hemisphere summer solar insolation is the main driving force for the Holocene climate change in Bangong Co. The climate fluctuated intensively during the last deglaciation, both the B/A warm period and YD event were recorded by the sediments. In the early-Holocene, ISM strengthened and climate became warm and wet. With the decrease of the solar insolation, the climate shift in the mid-Holocene. A dry and cold climate prevailed in in late Holocene due to the weakened ISM.