| Qaidam Basin, on the northeastern Qinghai-Tibetan Plateau, is part of the arid central region of Asia. Its ecological environment is vulnerable and the climatic and environmental change is dramatic. Influenced by the westerly jet, and Asia's southeastern and southwestern monsoons, the basin is very sensitive to regional and global climate change. Land cover change and the dust it produces in the Qaidam Basin may influence regional and hemispheric climate. Therefore, research on the paleo-climate and paleo-environment of Qaidam Basin could not only help to clarify the environmental history of China's arid northwest, but could also have important applications for the study of Past Global Changes (PAGES).Gahai Lake, located in eastern Qaidam Basin, is a sub-magnesium sulfate lake. A 37.05m core was obtained from the edge of Gahai Lake. A climatic and environmental history of the Gahai Lake area since the Late Deglaciation period was reconstructed based on AMS 14C dating and a combined analysis of mineral composition, loss-on-ignition (LOI), carbonate content, geochemical element proxies, and carbon and oxygen stable isotopes of authigenic carbonate in the lake sediment. The core contained sediment from four climatic periods: 1) the Late Deglaciation period (12710-11360 cal. aBP), including the relatively warm and wet Aller?d period (12710-12380 cal. aBP) and the very cold and arid Younger Dryas period (12380-11360 cal. aBP); 2) the early Holocene period (11360-8730 cal. aBP), which was rather arid with rising temperatures and a fluctuating climate; 3) the Mid-Holocene period (8730-3200 cal. aBP), which featured the mildest climate conditions since Deglaciation, with a warm and wet early stage (8730-5390 cal. aBP) and a cool but arid late stage (5390-3200 cal. aBP); and 4) the Late Holocene period (3200-0 cal. aBP), with a cold and very arid early stage and warmer but more arid late stage. It was cold and wet in Little Ice Age (LIA). The results also indicate that the Younger Dryas climate was not always cold and arid; the record of climate fluctuation found is similar to that of theGuliya ice core (Yang et al, 1997) and a transition zone between desert and loess (Zhou et al, 1996). In contrast to some previous researches, the findings show that 8730-5390 cal. aBP was a stable period with a warm and wet climate. The findings also show that 3500-3800 cal. aBP, 4400-4560 cal. aBP, and 5100-5200 cal. aBP were cold and arid periods, confirming earlier studies at home and abroad. A wet-warm event at about 1500 cal. a B.P. was also detected.The levels ofδ18O are an important indicator of climatic change, reflecting the ratio of evaporation and precipitation in the lake catchment. The level ofδ13C does not provide a clear indication of climatic change, because many other factors influence it. Low carbonate content in lake sediment is typically due to a wet environment. At a depth of 430-1270cm in the Gahai Lake core other measures point to arid climatic conditions, but the carbonate content is low. A possible explanation of this is that discontinuous fresh water input diluted the concentration of Ca2+, lowering the carbonate content. Variations in the levels of Sr/Ba and Si/Al reflect the salinity and chemical weathering intensity of the lake catchment fairly well.Based on an analysis of climatic and environmental changes in Gahai Lake since the Late Deglaciation period, we hold that Gahai Lake's climate has been influenced by changes in the coupled ocean-atmosphere-land climate system, which was affected by variation of solar radiation.
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