The Research Of Correlation Relationship Between Evolution Of Typical Lakes And Lakeside’s Aeolian Sediments Within Tibetan Plateau

As the largest and highest plateau on earth,the Tibetan Plateau（TP）is known as the"Third pole of the world".In addition,it is located in the interaction area of East Asian monsoon,Indian monsoon and prevailing westerly wind,which makes the TP extremely sensitive to climate change.Since the 1980s,the TP has attracted more and more attention,and has become another research hotspot after the South Arctic.Moreover,due to the sensitivity of the TP to climate change,it plays a"Driver"and"Amplifier"role in the study of global climate change.As the largest lake distribution area in China,there are thousands of lakes in the TP.Because most of the lakes are located in arid and cold areas at high altitude,the wind erosion in the lake area is more serious than that in other areas,resulting in a large number of aeolian sediments near the shore of closed lakes on the TP.Therefore,the closed lakes on the TP and their lakeshore aeolian sediments are an ideal goal to study climate and environmental change,retrieve regional precipitation and temperature,and explore the relationship between lakes and lakeshore aeolian sedimentation.In this study,Qinghai Lake and Gahai Tan Lake in the northeast of TP,Zhari Namco,Dawa Tso,Dagze Co and Tanqung Co in the southwest of Qinghai Tibet Plateau were selected as the study areas.A total of 40 OSL dating samples,12radiocarbon dating(AMS ¹⁴C)samples and several geochemical index samples were tested and analyzed.Based on the OSL and ¹⁴C dating results,a reliable age framework is established,and the lake range change and paleoclimate change in the study area are reconstructed by using sedimentary facies analysis,digital elevation model（DEM）data and Tra CE-21 ka model,combined with the results of environmental proxy indicators such as particle size,magnetic susceptibility and total organic matter（TOC）,The evolution of each lake during Holocene and its correlation with lake shore aeolian sediments are analyzed and discussed.Based on the above work,the main conclusions are as follows:1.During the past evolution of Qinghai Lake in the northeast of the TP,Zhari Namco,Dawa Tso,Dagze Co and Tanqung Co in the southwest of the TP,the range of lakeside aeolian sediments and the range of lakes show a relationship of ebb and flow.That is,during the period of high lake level,the range of lakeside aeolian sediments was shrinking;During the low lake level period,the range of lakeside aeolian sediments expanded continuously.2.The lacustrine samples of the CQ section are dated by OSL and ¹⁴C,and the two dating results are analyzed.The results of OSL age are more reasonable and accurate than those of ¹⁴C age.Due to the existence of the carbon pool effect,there is a certain overestimation of ¹⁴C age,and different dating materials are affected by the old carbon effect.Among them,the age of aquatic plant residues is less affected by the old carbon effect than that of large organic matter.Although terrestrial plant residues are not affected by the old carbon effect,due to the uncertainty of their death time and deposition time,it should be cautious to use the ¹⁴C age of terrestrial plant residues as the formation age.3.Since 21 ka,the precipitation and temperature in the southwest of the Tibetan Plateau have shown an upward trend,and almost all the maximum precipitation occurred in the middle Holocene.The reason for this phenomenon is that the Asian summer monsoon（ASM）has increased due to the enhancement of solar radiation in the Northern Hemisphere.In addition,the Tibetan Plateau is mainly controlled by ASM.Therefore,the water carried by ASM has increased,resulting in the increase of precipitation in the Tibetan Plateau.4.During the early Holocene（11-9 ka）,the water level of Qinghai Lake was low,the lake range was close to the lake basin,a large range was exposed and eroded by wind,which provided a large number of material sources for the downwind area on the east bank.Therefore,a large amount of aeolian sand accumulated on the East Bank of Qinghai Lake;During the middle and late Holocene（7-1.2 ka）,Qinghai Lake had a high lake surface many times,and the originally exposed Lake Basin was covered by lake water,which was difficult to be eroded by wind.5.Zhari Namco and Dawa Tso had the largest lake range in the early Holocene.The weakening of monsoon and the gradual decline of summer temperature gradually reduced the precipitation and glacier melt water in the two lake areas,which also led to the continuous shrinkage of the lake range from the early Holocene to the middle Holocene,which has continued to this day.The aeolian sediments widely distributed on the banks of Dawa Tso and Zhari Namco are mainly aeolian sand.In addition,the scope of the lake is shrinking,and the aeolian sand is continuously deposited in the exposed lake basin.There is a negative correlation between the Lake range and the aeolian sand range.6.During the period from LGM to middle Holocene,due to the strengthening of monsoon and the rise of temperature,the regional climate changed to warm and humid,and the lakes expanded continuously.Since the middle Holocene,the lake water level has been declining due to the weakening of the monsoon and the decline of temperature.Although the aeolian sand near the two lakes is deposited on the surface and thin,it is undeniable that the range of aeolian sand on the lake bank is still negatively correlated with the lake water level.In addition,compared with the impact of climate change on the range of lakes and lake shore aeolian sediments,the influencing factors of human activities are smaller.