Holocene Environmental Evolution In The Badain Jaran Desert,Revealed By Phytolith Assemblage From Lake Sediments And Peat

Badain Jaran Desert is located in the transition zone between East Asian monsoon region and westerly region.It is sensitive to climate change and is an ideal area for paleoenvironmental research.In this paper,phytoliths were extracted from133 samples of ZZH and 72 samples of TR buried peat layer in the hinterland of Badain Jaran Desert.A total of 67998 phytoliths were identified.Seven AMS¹⁴C data of ZZH section and 11 AMS¹⁴C data of TR section are selected to establish the profile chronological sequence.Based on the reliable AMS¹⁴C dating,by analyzing phytolith data and assemblage characteristics,the phytolith index,ordered clustering,principal component analysis and weighted average partial least squares regression(WA-PLS)were used to reconstruct the environmental evolution characteristics and climate background of peat formation in Badain Jaran Desert since Holocene.And compared with previous studies,the climatic changes and driving mechanisms on the millennium and centennial scales in the region are deeply discussed,and then the reliability of phytolith inversion of the environmental evolution of the monsoon margin is discussed.The main results and conclusions are as follows.1.The types of phytoliths in lacustrine sedimentary section and buried peat layer of Badain Jaran Desert are very rich.The typical types of phytoliths are rondel,wavy-trapezoid,point,saddle,square,rectangle,fan,etc.At the same time,sponge spicules and diatoms are found in the section.Phytolith analysis results show that phytoliths in lacustrine sediments and buried peat in Badain Jaran Desert hinterland are mainly herbaceous phytoliths,with a small amount of woody phytoliths.2.The phytoliths well respond to the environmental evolution of Badain Jaran Desert,revealing that the climate in the region was relatively humid in the early Holocene and early Middle Holocene,reached the wettest period in the Middle Holocene,and showed the characteristics of cold and dry in the Late Holocene,which is consistent with other research results in the monsoon marginal area.The reconstruction results show that the environmental evolution of Badain Jaran Desert since Holocene has experienced six climatic and environmental evolution stages:warm-wet(11?9.8 cal ka BP),cold-wet(9.8?7.8 cal ka BP),warm-wet(7.8?4.6 cal ka BP),warm-dry(4.6?3.4 cal ka BP),cold-dry(3.4?2.1 cal ka BP)and cold-dry(2.1 cal ka BP).The retrieved regional temperature change is basically consistent with the change of 65°N summer solar radiation,which indicates that the change of summer solar radiation in the northern hemisphere is the key factor driving the regional environmental change.The evolution of lakes in this region is basically synchronous with the evolution of climate and environment in this region,and the level of lake water is affected by the regional climate change.3.The reconstruction results accurately reconstructed several cold and dry climate events in the region,which were 9.2?9.4 cal ka BP,8.2 cal ka BP,5 cal ka BP,4 cal ka BP and 3 cal ka BP.The time of these dry-cold events basically corresponds to that of the North Atlantic cold events,which indicates that the region is related to or teleconnected with the high latitude climate change in the northern hemisphere during the weakening stage of the East Asian monsoon.4.The buried peat layer can be used as a sign of the beginning of Holocene in this area.The warm index of phytolith in the formation period is low,and the content of cold type phytolith is high,which indicates that the temperature in this period is relatively low,while the concentration of sponge spicules and diatom in the section is high,indicating a humid environment.The reconstructed temperature change shows that the average temperature during peat formation is about 8.8?,which is about 2.3?lower than the annual average temperature in modern desert hinterland(11.1?).Therefore,peat layer is formed in low-lying area under the condition of low temperature and sufficient rainfall and groundwater recharge.