Assemblage Of Ostracods And Environment Changes Of Lake Donggi Cona In Northeastern Tibet Plateau Since Holocene

Because of the emergence of global environmental problems, the study of ancient climate changes are becoming more and more important. The Tibetan Plateau of China is one of the most sensitive areas of global environmental changes, for the disturbance of human activities are less there. And the large number of closed to semi-closed lakes distributed on Tibetan Plateau are good sediment material which could carry a lot of information of paleoclimate and have advantages like good continuity, high sensitivity and high resolution. The climate changes could be amplified in the record material. And this area is an ideal place to reconstruct paleoclimate and the law of environmental changes.This research is focused on Donggi Cona lake which located in Northeastern Tibetan Plateau, China. And this paper will reconstruct the paleoclimate since Holocene of this area, with the study about the sediment proxy, assemblage of ostracods, of section P14in Donggi Cona lake, and combined with some other proxies including age model, TOC and carbonate content. In the end of the paper, the comparison to the other lakes in this region was made, hoping to rebuild and describ the paloenvironment and paleoclimate records. The main conclusions are as follows:(1) A total of ostracods with10genera and12species are identified, including a comparison species. The most important species including Eucypris dulcifons (Diebel and Pietrzeniuk,1975), Heterocypris salina (Brady,1868), Limnocythere inopinala (Baird1843), Sarscypridopsis aculeata (Costa,1847), Ilyocypris sebeiensis (Yang and Sun2004), Tonnacypris cf. edlundi (Van Der Meeren, Khand&Martens,2009), Fabaeformiscandona rawsoni (Tressler1957), Trajancypris clavata (Petkovski,1964). The change of Ilyocypris sebeiensis and Tonnacypris cf. edlundi are quite same so we consider them to be symbiotic species and the former one has a stronger adaptablity of different habitat, which could be seen as a referenced species of flowing waters. (2) The characteristics of climate chages in this area could be summarized as follows:during10150-9050cal year BP, climate is a dry and cold; during9050-8350cal year BP it improved and then transformed into warm condition; until8350-7250cal year BP, it began a transitional climate which had the gradually increasing temperature and humidity; during7250-3900cal year BP, it’s warm and humid which could be called as the suitable period; and about5100cal year BP when the lake reaches the maximum depth and may become an open lake; after3900cal year BP, it is the period which the lake shrinked, as the same time, climate gradually changed to dry climate. The general trends are consistent with other studies of Donggi Cona and the other lake in this region, such as Qinghai lake. But when compared to the lake in Southereastern margin of the Tibetan Plateau, like Koucha lake, we noticed that the changes of paleoclimate are not so much alike. The formation mechanism of the climate should be considered here to explain this phenomenon.