Holocene Palaeoclimate Chages In The Regions Of Qinghai And Gansu Province

The regions of Gansu and Qinghai provinces are vast drylands in west interior of China, representing a key region that climaticlly links the East Aaian summer monsoon (EASM), the India summer monsoon (ISM) and the westerlies. The reginal geomorphology is complex and this desert-loess boundary belt is a cross zone among the desert, loess and Tibetan Plateau. Because of the special position, the region is increasingly becoming the ideal regions of palaeoclimate research.We selected four areas(GSK0305 core from Lake GasHure from Qaidam Basin, JZ0611 core from Jianzha County in Qinghai province, GHTG0705 section from Gonghe County in Qinghai province, CX0706 section fom Jingyuan County in Gansu province) in Gansu and Qinghai provinces as our targets and reconstructed the paleoenvironmental evolution history with MS (mass magnetic susceptibility) and the color (L*,a*,b*) proxy data during the Holocene. In the course of analyses and comparisions with other records we come up with the main viewpoints as follow:1. The result suggests that the climate of lake Gashure and other lakes loacated at Qaidam Basin was humid during the mid Holocene and the early late-Holocene, and become drier since the middle of late-Holocene. The reavealed history of climate change in Qaidam Basin during the Holocene was approximately consistent with the evidence of a westerly dominance, thus we conclude that the palaeoclimate of Qaidam Basin was mainly controlled by westerly during the Holocene.2. Jianzha and Gonghe Counties, located at the edge of monsoon affected regions, are believed to have been controlled by both East Aaian summer monsoon (southeast monsoon) and India summer monsoon (southwest monsoon). The comparison results show that the Jianzha and Gonghe Counties were affected mainly by India summer monsoon (southwest monsoon), and our proposal is supported by some evidence as well.3. The climate of monsoon-dominated region was mostly forced by changes in low-latitude summer insolation during the Holocene. Southeast monsoon emanated from low- and mid-latitude ocean delayed 1000～ 2000 years than southwest monsoon emanated from low latitude ocean in response time to summer insolation. Our research indicates that the initiation and ending of Holocene Climate Optimum (HCO) in Jingyuan record more than one thousand years lagged than of Jianzha and Gonghe records and the conclution also support the idea that Jingyuan was affected mainly by southeast monsoon during the Holocene.4. Because of the enhanced solar insolation, the. great ice-sheet in north hemisphere completely disintegrated in mid-late Holocene and both high SST and enhanced air temperature might increase moisture transport by westerlies, leading to a humid climate in Qaidam Basin during the mid Holocene and early late-Holocene. After the middle late-Holdcene, the precipitation decreased, for the solar insolation was weakened and westerlies moisture declines.