The Research On Climate Instability In The Mu Us Desert During The Last Glacial Period

The Last Glacial Period was the closest one to human beings in the Quaternary Period.The climate was dry and cold as a whole,but there were many climatic changes and warm and cold fluctuations.To deeply study the characteristics of climatic instability in this period is of great significance for human beings to deeply understand short-term climatic changes and to predict and cope with future climatic changes.In recent years,D/Omestic and foreign scholars have carried out systematic research on climate change since the Last Glacial Period in deep-sea deposition,loess deposition and stalagmite deposition,and achieved significant results.The results all show that a series of rapid and high-frequency climate fluctuation events with the millennium scale occurred in the Last Glacial Period,but the understanding of climate fluctuation and short-term events is not deep enough,and the research on the driving mechanism of climate change system is still insufficient.Located at the edge of the East Asian monsoon,Mu Us Desert is sensitive to climate change and is an ideal area for studying climate change.Rich paleoclimate information is preserved in the lacustrine sediments,which can reveal the changes and instability of the sandy climate and environment.Therefore,this paper makes a field investigation on the fluvial-lacustrine section of MJW in the southeast margin of Mu Us Desert,grain size,magnetic susceptibility and chemical elements are selected as proxies,combined with OSL dating and stratigraphic sedimentary characteristic,that lacustrine sedimentary records of the Last Glacial Period in Mu Us Desert are comprehensively studied based on the field investigation of the MJW fluvial-lacustrine facies section in the southeastern margin of Mu Us Desert,and compared with the Dansgaard-Oeschger cycle event（called D/O event）recorded by the GRIP ice coreδ¹⁸O and the Heinrich event（called H event）in the North Atlantic Ocean,the characteristics of climatic instability in Mu Us Desert are revealed.The following conclusions have been preliminarily drawn:（1）The sedimentary sequence of alternating aeolian sand and fluvial-lacustrine facies in MJW section of Mu Us Desert since the Last Glacial Period.Grain size,magnetic susceptibility and chemical element indexes show regular and obvious peak（high value）and valley（low value）fluctuation.Fluvial-lacustrine are developed in warm and humid climate,and the content of fine particle components is high and the particle size is fine under strong chemical weathering,and the oxidation environment is conducive to the refinement and enrichment of magnet mineral,so the magnetic susceptibility of rivers and lakes is large,Al₂O₃ and Fe₂O₃ are stable and high in content,and soluble elements are leached out;In the dry and cold climate,aeolian sand accumulates,with coarse sediment particle size,weak mineral magnetism,low magnetic susceptibility and less Al₂O₃ and Fe₂O₃ content.（2）Combined with previous studies and the climatic changes experienced by Mu Us Desert revealed by the MJW section,the climatic changes during the last glacial period can be divided into:the last glacial early glacial stage（～57ka BP）,the climate was dry and cold on the whole,but there existed secondary multiple warm-wet fluctuations,in which aeolian sand accumulation occurred,sandstorm activity was active,and river-lake facies development still existed;During the last glacial stage（57～23 ka BP）,the changes of temperature,dry and wet were more frequent,which were further divided into three sub-stages:during the subglacial stage（57～46 ka BP）,the stage showed weak temperature and humidity,with less accumulation of aeolian sand in the early stage,development of river-lake facies,shallow lake environment and relatively warm and humid climate;Subglacial stage（46～35 ka BP）,during which there was a short cold-dry period,with aeolian sand accumulation,gradually shrinking lake and slight climatic fluctuation;（35～23 ka BP）of subglacial stage,characterized by relatively strong warm and wet periods,with the development of river and lake facies layers,but with the development of aeolian sand,dry and cold weather events,and relatively high vegetation coverage.After 23ka BP,the lake facies developed,but the aeolian sand accumulation D/Ominated,and the whole was dry and cold,with frequent climate fluctuations.This further confirms the fact that the climate in Mu Us Desert has been rather unstable since the Last Glacial Period and it also indicates the sensitive response of the region to climate change.（3）Since the Last Glacial Period,the aeolian sand and fluvial-lacustrine interbedding deposition in the MJW section of Mu Us Desert land have been characterized by the ebb and flow of the east Asian winter and summer monsoon.The 15 winter monsoon events and 15 summer monsoon events in Mu Us Desert revealed by 15 warm-wet/cold-dry alternations have corresponding D/O cycles recorded byδ¹⁸O in GRIP ice core and H events in the North Atlantic,and they have good temporal consistency,further supporting the possibility that high-frequency climatic fluctuations during the Last Glacial Period may have some connection with the North Atlantic region.In addition,it is consistent with other sedimentary records in East Asia and global ice core records,thus inferring that the climatic instability of the Last Glacial Period was in response to global changes.The variation of the intensity of the East Asian winter and summer monsoon in Mu Us Desert is controlled by the variation of the ice amount caused by the solar radiation in the northern hemisphere,which also indicates to some extent that the driving force of the land-ocean-atmosphere system process of the Asian monsoon climate system also plays a key role.