Loess Recorded Climatic Change Since The Last Interglaciation In The Northern Foot Of Tianshan Mountains

Climatic change since the last interglaciation is one of the hot topics in the study of the ancient climate.Conducting a systematic study of climatic change since the last interglaciation,and finding out the reason of climatic change in the history of earth evolution will help us to understand the global climate system better.Xinjiang is located in the arid region of central Asia,whose climatic change is very complicated.The systematic study of climatic change since the last interglaciation in Xinjiang is few up to now,we are still lack of understanding to the drying history and the drive system of climatic change of this region.In order to advance the study of ancient climate of here,we selected a loess section which is in the northern foot of Tianshan mountanis,measured and analyzed grain size distribution,organic matter content and environmental magnetic parameters.Beyond that,we contrasted our parameters with the deep sea oxygen isotope curve,and by comparison we got some accurate age control points.Then with these points,we rebuilt the history of climatic change in Xinjiang since the last interglaciation.At last,we contrasted the history of climatic change with other loess records in the westerly dominant area of inland Asia and the climatic record of the oxygen isotopic composition of Greenland GRIP ice core.The main indicators were obtained through the analysis as follows:The results show that the content of magnetic mineral of the section is much lower than Loess Plateau of China,and the dominant magnetic mineral is ferromagnetic.Native strong magnetic mineral is the primary cause of magnetic susceptibility rise.The analysis of grain size of magnetic minerals indicates that the property of the loess is coarser.The grain size of loess is composed mainly of silt,which is similar with Loess Plateau of China and other loess sections in Xinjiang.The dust transported by surface wind is the main component,and the dust transported by altitude air is little.The organic matter content is low,and there is a little change of the content in the whole section.The characteristics of climatic change since the last interglaciation in Xinjiang could be divided into four parts,we will explaining them respectively.First,before the last interglaciation(148.6?130ka BP)the wind power was strong and the climate was arid.Second,during the last interglaciation we could more divide it into three sections.During the period of 130?120ka BPR the wind power was weak,the climate was arid because of the rapid increase of evaporation capacity.Even so,there was also a paleosol developed.Then,during the period of 120?96ka BP,the wind power became stronger and the climate became more arid.Finally,during the period of 96?71 ka BP,the wind power was weak and the climate was wet,and there was a clear paleosol developed in this time.Third,when the last interglaciation was gone,then the last glaciation was coming.On the basis of the characteristics of climatic change,this period could also be divided into three sections.During the period of 71?57ka BP,the wind power was strong,the climate was wet because of the rapid decrease of evaporation capacity.Then,during the period of 57?29ka BP,the wind power became weaker and the climate became more wet.Finally,during the period of 29?14ka BP,the wind power became stronger again,with the change of the wind power,the climate became more arid.Fourth,since the 14ka BP,the climate was becoming warmer and wetter in total,because the parameters show that the wind power was becoming weaker and the climate was becoming wetter.The climatic record of the Baiyanghe loess since the last interglaciation has a good corresponding relation with other loess in the westerly dominant area of inland Asia.The parameters show that during the glaciation,all the loess sections record that the wind power is strong and the climate is arid.Then,during the interglaciation,the wind power is weak and the climate is wet.These research results show that the characteristics of climatic change since the last interglaciation have no clear difference in the westerly dominant area of inland Asia.Then,we contrasted loess records in the westerly dominant area of inland Asia and the climatic record of the oxygen isotopic composition of Greenland GRIP ice core.The results show that they have a good corresponding relation not only in the orbital scale but also in the sub-orbital scale.Besides,the results show that loess section in the westerly dominant area of inland Asia also recorded the climate fluctuation in the North Atlantic Ocean in the last glaciation,which shows that climatic change since the last interglaciation in the westerly dominant area of inland Asia have a close relation with the North Atlantic Ocean.