On environment character of the Gahai Lake in the Holocene Hypsithermal

As a closed inland lake, Gahai Lake is located in Delingha Basin, the northeast Qinghai-Tibet Plateau. It is very sensitive in the response to climate change and is the ideal location to study the regional environment response to global change. Based on comprehensive analysis of granularity, magnetic susceptibility and pollen in DG02 core obtained from the west-northern margin of Gahai Lake, this article emphasized the ancient climate character of the Gahai Lake in the Holocene Hypsithermal. The mean pollen concentration in this phase was up to 4100 grain per gram and the pollen percentage objectively reflected the vegetation status. The research result showed that after the cold moisture phase of the early Holocene, the temperature in the area increased gradually to the tiptop and turned into the optimum climate in 7.9~5.1 cal aB.P. Acoording to the character of the pollen assemblages, granularity and magnetic susceptibility, the author deducted that with the higher temperature, the lower precipitation, the Asian monsoon was weaker, all substituted index revealed the dry and worm climate pattern in the middle Holocene here. The plentiful continuance thawy mountain glacier might made the lake water deeper and more vast. The far-ranging sedge swamp lied on the gently and flat lake bank.