Paleoenvironmental Reconstruction Of Lake In The Hinterland Of Badain Jaran Desert Based On Palynology During Early-middle Holocene

The lake group in the Badain Jaran Desert has a unique water circulation mechanism,and the sediments of these lakes record important information about past climate changes in the Badain Jaran Desert.Due to the fragility of the arid ecosystem,the ecological environment of the Badain Jaran Desert is extremely sensitive to climate change（especially humidity）,making it an ideal place for paleoclimate reconstruction.The reconstruction results help to deepen the understanding of the environmental evolution history of the Badain Jaran Desert and explore its possible climate response mechanisms,providing a reference for the sustainable development of water resources in the Badain Jaran Desert.Therefore,this study selects the lake and peat deposits of the Taerlegtu（TR）paleolake located in the hinterland of the Badain Jaran Desert as the research object.With a reliable chronological scale established through AMS¹⁴C dating,the lake level and internal environment are reconstructed based on grain size,mineral composition,TOC,TN,C/N,δ¹³C_org,and other geophysical and chemical indicators;the regional vegetation,algae,animal activity history is reconstructed using the pollen-algae-charcoal-fungal spore method.Through the above methods,this study reconstructs the environmental evolution history of the Taoerlegetu paleolake during the early and middle Holocene（10.9-5.5 cal kyr BP）,compares it with existing Holocene reconstruction records of the Badain Jaran Desert,and attempts to explore the response mechanism of the Badain Jaran Desert to global climate.The main conclusions are as follows:（1）The abundant local pollen,represented by the Artemisia genus,and high pollen concentration during 10.9 to 7.3 cal kyr BP indicate a period of lush vegetation,known as the"Artemisia period".However,a significant vegetation decline followed,with low pollen concentrations and a higher proportion of exogenous tree pollen between 7.3 and5.5 cal kyr BP,suggesting relatively sparse vegetation during this period.（2）Based on the lake water level reconstruction results fromδ¹³C_org and particle size,combined with algal and pollen data,Lake Torellengen was in a peat period between 10.9 and 9.1 cal kyr BP,had a higher water level between 9.1 and 7.3 cal kyr BP,and experienced a water level decline after 7.3 cal kyr BP.This result is consistent with evidence of high lake levels during that time period.（3）The lush vegetation during the"Artemisia period,"which corresponds to a period of lower regional precipitation,suggests that the vegetation in the hinterland of the Badain Jaran Desert during the Early Holocene was mainly influenced by factors beyond regional precipitation.Therefore,this study proposes that the hinterland of the Badain Jaran Desert during the Early to Middle Holocene may have been influenced by groundwater transport from distant regions（possibly from the Qilian Mountains in the northeast margin of the Tibet Plateau）.In the Early Holocene,higher summer temperatures and ice accumulation led to more meltwater,resulting in the"Artemisia period"in the desert hinterland.However,the sudden vegetation decline after 7.3 cal kyr BP may be related to temperature changes and reduced meltwater caused by decreased ice accumulation in the Qinghai-Tibet Plateau.（4）The cold environment of the Early Holocene in the Badain Jaran Desert was unfavorable for organic matter decomposition.The abundant meltwater supply from the Qilian Mountains provided sufficient water,leading to the development of a cold and humid non-zonal microenvironment,which led to the formation of peat during this period.This indicates that the peat layer in the Early Holocene in the Badain Jaran Desert is a typical climate layer and to some extent indicates the transition of regional climate into the Holocene.This is consistent with evidence from sand wedge and nitrate layers in the Hexi Corridor and the outer edge of the Badain Jaran Desert and can be used to further determine the regional division of the Younger Dryas Period（YD）and the Holocene,known as the"Jindingzi"period.