Abstract: Millennium-scale climate changes such as Heinrich events and Dansgaard-Oeschger cycles,occurred in North Atlantic region in the last glacial period have a wide range of records around the world,which included,for example,the marine deposit in the Arabian Sea and the loess and stalagmite in East Asian monsoon region.As a transitional westerly-edge-zone to monsoon region,Ili area located in Xinjiang Province,China,is sensitive to climate change.Relevant studies show that millennial-scale climate events are recorded in Ili loess,but how millennial-scale fluctuations affected this region needs a further answer.As an important geological record restoring the paleoclimate information,the loess in this area is beneficial to the study of the above problems.This study selected Zeketai section in the Ili Basin as the research object.The section has 20.35 m thickness and was sampled at 5 cm interval.Finally 407 samples were obtained.The end member analysis was processed for the grain size of loess above 12 m in this profile.The result showed that the grain size distribution in this profile suited to yield four Gen.Weibull endmembers with modal size of 0.8 μm(EM1),8 μm(EM2),25.1 μm(EM3) and 51.6 μm(EM4) respectively,representing pedogenic component (EM1),upper-level westerly wind (EM2) and dust storm (EM3 and EM4).However,EM4 is more capable of reflecting the expansion of the Siberian high pressure in Ili area during the last glacial period.Both EM2 and EM4 can record the fluctuations of the Millennium-scale climate,but the response degrees of the two EMs are different.When H events occur,EM4 content gets increased and EM2 content gets decreased.When the cold events occurred,the ice volume in the northern hemisphere was increased,and the increased cold air in the Arctic region strengthened the Siberian high pressure,and then expanded into the Ili area,resulting in a large dust storm weather.Under the westerly wind transport,the dust was accumulated on the north bank of the Goness River.However,the blocking of the Qinghai-Tibet Plateau divided the westerly belt into two branches in winter,and the main axis lies on the southern side of the Himalayas,so the influence of Westerlies on the region is weakened.During the whole glacial period,the Westerlies belt moved southward for a long time and the main axis was southward.When the cold event occurred,the Westerlies belt remained in the south.During 51.3~20 ka,millennial-scale events are more obvious in EM4 content change curve; After 20 ka,YD and H1 events are more outstanding in EM2 content change curve.This suggests that both Siberian high pressure and Westerlies are the important spread mechanisms of millennial-scale climate changes.The cause of the above difference is likely to be the change of global ice volume driven by solar insolation on the orbital time-scale.In addition,regional factors also influence the grain size change in Zeketai.

Key words: millennial-scale climate change, endmember analysis, Zeketai, Westlies, Siberian high pressure