Climate Change Since Deglaciation Recorded By Lacustrine Sediments In Mu Us Sandy Land

The climate of the Holocene is one of the important research contents of the Past Global Change(Pages).With the continuous discovery of highresolution sedimentary facies climate information carriers,the climate instability of the Holocene has become a hot topic for scholars to study.The cognition of the climate change of the Early and Middle Holocene is controversial and needs to be further studied.Mu Us Desert is located in the sensitive zone of climate and environment.It is an ideal place to study climate change.However,in the past studies of paleoclimate and paleo-environment since Holocene,more attention has been paid to climate change reflected by aeolian sedimentary sequence.The lacustrine sediment in the desert itself preserves a lot of climate and environment information and is a good carrier to study the climate and environment change in the desert.The aeolian sand is the activation of dunes and the expression of the positive process of desertification,while the lacustrine sediment and palaeosol development represent the fixation of dunes,which is the reverse process of desertification.Therefore,this paper comprehensive analysis and research of lacustrine sediment in Mu Us Desert,based on the southeast margin of Mu Us Desert for field,LT profile in OSL dating,on the basis of the particle size,chemical elements,organic carbon and other proxies,considering different particle size and chemical elements such as proxies and connecting with the strata sedimentary characteristics,establish the ancient climate record sequence,to further understand the paleoclimate change and paleo-environment evolution process of Mu Us Desert since the Early and Middle Holocene.The main conclusions of this paper are as follows:(1)The paleoclimate environment of Mu Us Desert was reconstructed by LT profile.The results show that before 16.79 ka BP,silty lacustrine facies developed,and the regional climate was warmer and wetter than that of the Last Glacial Maximal Age.During 16.79 ka BP to14.0 ka BP,The content of >63?m showed a rising trend,the sand activity was stronger than the last stage,the coarse particles were blown into the lake by wind,and the climate was dry and cold.From 14.0 ka BP to 12.3 ka BP,this period was equivalent to the B/A warm period of the North Atlantic in Europe,and the climate changed to warm and wet.From 12.3 ka BP to 10.94 ka BP,the climate continued to dry and cold after the YD cold event.From 10.94 ka BP to 5.8 ka BP,during the transition from Early Holocene to Middle Holocene,the area lakes in withdrawal period,the lake water level drops,atmospheric precipitation reduction,water in low-lying place,growth of aquatic plants in shallow water environment,under the condition of low temperature,organic matter decomposition is not completely turned into swamp facies,during the Middle Holocene,the grain size became finer,the elements were enriched,and the climate became warmer;Since 5.8 ka BP,the climatic and environmental conditions of Middle Holocene to Late Holocene changed from warm and wet to cold and dry,and gradually become close to the present climate and environmental conditions.(2)Based on the comparative analysis of the lake sediment records in the Mu Us sandy land,the climatic and environmental changes in the Mu Us sandy land are revealed: Deglaciation period(17.76?11.7 ka BP),the climatic fluctuations increased,the climate changes were more complex,and there were more aeolian sand deposits,lacustrine facies and peat development;During the Early Holocene(11.7?8.2 ka BP),the YD event ended,the climate warmed and the regional precipitation increased.The middle Holocene(8.2?4.2 ka BP)was the optimum period of Holocene,during which the temperature and precipitation were relatively high and the overall climate conditions were warm and humid.(3)A total of 161 data of lacustrine sediments have been obtained by using probability density statistical method.The analysis shows that the probability density of lacustrine facies in the Early and Middle Holocene is high,which is a high lacustrine stage with increased precipitation.The peat probability density is the maximum value in the Middle and Late Holocene.The peat development after 3.0 ka BP is closely related to the dry and cold climate,and the low temperature is easy to promote the increase of absolute humidity.In 3.9,6.6,7.5,8.1,11.4 ka BP,the peak values of the probability density of lacustrine and peat were mainly concentrated in the Middle Holocene,indicating that the Middle Holocene climate was relatively humid.(4)Environmental changes recorded by LT profile of lacustrine sediments in the Mu Us Desert during the Early and Middle Holocene were compared with regional lacustrine sediments,it is consistent with the sedimentary records of Moon Lake,Dali Lake,Wusulangzi Lake,ancient Zhuye Lake,Daihai Lake and Hulun Lake,B/A warm periods and YD events were recorded in the LT profile,with good regional and global contrast.Since the deglaciation period,the climate and environmental changes in the Mu Us sandy land are mainly controlled by the East Asian monsoon,which may be driven by a series of changes in each layer of the climate system caused by the intensity of solar radiation.