Study On Climate Change Of Hunshandake Sandy Land Since Mid-late Holocene

As one of the hotspots of global climate change research,the study of Holocene climate change not only helps to understand the characteristics of climate evolution over thousands of years,analyze the law of its interaction with human activities,but also provides strong theoretical support for the prediction of climate change trends.The study of the Holocene climate change in the northern monsoon marginal region of China provides a theoretical basis for understanding the evolution of the East Asian summer monsoon and its driving mechanism.Hunshandak sandy land is located at the edge of the monsoon,where is the agro-pastoral ecotone and the boundary between desert and loess.Based on the previous research work,this paper reconstructs the climatic change of Hunshandak sandy land since mid-late Holocene by using OSL dating method and using geochemical trace elements as substitution index.By comparing the two spatial scales of the region and the northern hemisphere,the climate change law of the Hunshandake Sandy Land since the middle and late Holocene was analyzed,and the climate driving mechanism was discussed in depth.The following three conclusions were obtained in this study :(1)In the vertical direction of TB profile,the change of trace chemical elements has certain regularity.In the paleosol layer and river-lake facies,the content of humid climate geochemical elements such as Cr and Rb is higher,and the peak value appears.Dry climate elements such as As and Sr are valley values.In the aeolian sand layer,the dry climate elements peak,and the humid climate elements are the valley values;the chemical element indexes of lake and marsh facies,such as Mn and Ba,reflect that there is more precipitation and hydrodynamic instability in the middle Holocene.It can be seen that the content of elements has a good indication of the paleoclimate,which can accurately reflect the paleoclimate environment during the formation of TB profile sediments.(2)In the TB section,the Holocene climate of the Hunshandak Sandy Land was inverted by using trace chemical elements as the indicator.The results showed that after5.81 ka BP,the Hunshandak Sandy Land experienced a process of summer monsoon from strong to weak,followed by a brief increase,while the climate changed from warm to dry to cold,then to warm again,and finally gradually approached the modern climate.(3)According to the previous research results,the paleosol of Hunshandak sandy land developed in the middle of Holocene,and in the early and late Holocene it was aeolian sand deposition period.Viewed from the section,the sedimentary characteristics of paleosol and aeolian sand in Hunshandake Sandy Land are alternately developed and interbedded.On this basis,the Holocene climate change of sandy land can be divided into three stages,namely,the Early Holocene warm and wet period(11.7～8.9 ka BP),the Middle Holocene warm and wet period(8.9～4.0 ka BP)and the Late Holocene fluctuating cooling period(4.0 ka BP).This process of climate change reflects the process of East Asian winter monsoon and summer monsoon fluctuating each other,and conforms to the trend of global mid-late Holocene climate change.