Holocene Lacustrine Deposit Record And Lake Evolution Mechanism In Badain Jaran Desert

Lakes are the center of life activities in arid regions.Studying its evolution process can help to understand the regional water cycle model and serve the sustainable development of local ecosystems.In the Badain Jaran Desert,about 110 perennial lakes are settling among the tallest dunes on earth and are typical groundwater-fed lakes.The study of lake evolution in Badain Jaran Desert mainly relies on the high-lake-level relics with spatial and temporal discontinuity lacking continuous lacustrine deposit records.The establishment of a continuous lacustrine deposit record in the Badain Jaran Desert can not only complement and improve the existing environmental evolution framework but also verify the environmental significance of lacustrine sediments'grain size,TOC content and mineral assemblage of groundwater-fed lakes in the sand sea,and a comparison of the record with the regional climate and environmental records can help to explore the evolution mechanism of the lakes in the Badain Jaran Desert.In this study,2 sections were excavated in the bottom of 2 dry lake basins named the Taoerlegetu?hereinafter referred to as TR?and the Zhunsulitu?hereinafter referred to as ZS?in the hinterland of Badain Jaran Desert,thus obtaining continuous lacustrine deposit samples.The grain size,TOC content,and mineral assemblage of the TR section were determined and analyzed.The AMS ¹⁴C dating method was used to establish the chronology,and the end-member-modeling algorithm?EMMA?method was used to extract the end members of the lake deposits part in the TR section.The grain size of the ZS section was determined and analyzed.The AMS ¹⁴C dating method was used to date the peat part of the ZS section and high-lake-level relics nearby.According to the lithology and grain size,the TR section and the ZS section can be divided into four sections that are,from bottom to top,the aeolian sand layer,the peat layer,the coarser and finer lake deposit layer.Comparing the proxies changes of TR section and the high-lake-level relics record,it is found that the grain size proxies of groundwater-fed lakes in the Badain Jaran Desert has multiple solutions when indicating lake depth change;the TOC content is difficult to be applied to lake depth change reconstruction due to its extremely low content;the salt mineral content is sensitive to the lake retreat,and its high value can indicate the process of lake retreat.According to the lithology and proxy changes of the TR section,and comparing the ZS section and the high-lake-level relics record,it is considered that the TR paleo-lake was in a swamp state during ca.11,000⁹,500 cal BP,the water table was close to the ground and developed peat;during the period of 9,500⁶,500 cal BP,the depth of TR paleo-lake continued to rise and reached a maximum during the period of ca.7,500⁶,500 cal BP;during the period of ca.6,500⁴,000 cal BP,the depth of TR ancient lake gradually decreased;after ca.4,000 cal BP,the TR paleo-lake quickly retracted and dried up.The depth change record of TR paleo-lake was converted to the lake water level and groundwater level record through the relationship between the lake and the groundwater in the Badain Jaran Desert.Comparing the lake level,the groundwater level record and the effective moisture record of the desert hinterland indicated by the age distribution of the plant calcareous root tubes,it is found that the Holocene lake-level changes are in response to the change of effective moisture in the desert hinterland;during the high-lake-level period,the increase of groundwater recharge rate is synchronized with the high effective moisture condition in the desert hinterland.During the glacial-interglacial transition period,the arid environment in the desert hinterland could not explain the rise of the groundwater level,and it was speculated that the Badain Jaran Desert Lakes are linked to regional climate and environmental changes through the groundwater system.The meltwater from the regional cryosphere during the late glacial period and the early Holocene may fill the aquifers of the Badain Jaran Desert that have been depleted since the last glacial period through regional groundwater system,that laid the foundation for the development of lakes.