A 1600-year Eolian Activity Record From Jili Lake,North Xinjiang

The arid region of the central Asia is one of the most inportant source areas for global dust.The reconstruction of changes in the past atmospheric dust in this area can provide insights into understanding of global atmospheric circulation.Here we present the results of multi-proxy analysis of two sediment cores from Jili Lake in northern Xinjiang.Cores JL18-01-A and JL18-02-A were drilled from the central area and the southwest part of the lake,respectively.Based on the stratigraphy and the accelerator mass spectrometry?AMS?¹⁴C dating results of the two sediment cores,the evolution of the Jili Lake was explored.In combination with analyses of grain-size compositions and Loss-on-ignition?LOI?variations of sediments in the lake basin,the regional eolian activity and climate change over the past 1600 year were reconstructed.The main conclusions are as follows:1.The ¹⁴C specific activity values of the lake-water DIC sample and the samples from the upmost layers of cores largely approximate to the pMC?percent modern carbon?values of the modern atmosphere,reflecting that the“reservoir effect”of the lake water is weak.This may be related to the fast hydrological cycle of the lake and the wide distribution of silicate rocks in the basin.Consequently,we used the ages from the upper parts of the cores to establish the chronological frames of the two cores.The chronology was obtained by linear interpolation between two adjacent calibrated ages.2.The results of the stratigraphic and the AMS ¹⁴C dating of the two sediment cores reflect that the lake have experienced the following stages:during the last deglaciation?14.8-10.8 ka BP?,the brownish-red fluvial sediments suggest that the lake basin has been filled by fluvial processes and that the lake has not formed yet.Subsequently,there are obvious sedimentation hiatus in the two cores.Until 4.5 ka BP,the offwhite clayey-silt lacustrine sediments occurred in the southwest of the lake,indicating a shallow lake environment at the site.However,the deposition terminated at³.0 cal ka BP,followed by a sedimentary hiatus spanning a spell of¹000 years.Till 2.4 cal ka BP,the gray lacustrine sediments with high contents of organic matter deposited after the hiatus,which imply that a deep-lake environment began to form.Since 1.6 cal ka BP,the similar lacustrine sediments also appeared in core JL18-01-A,indicating that the lake may have expanded to the modern scale.3.The grain size composition of sediments in the lake basin indicate that,the>200?m fraction in the lake surface sediments is sensitive to the change of the distance between the sampling site and the lake shore and hence can reflect changes of the lake level,and that the 40-200?m fraction is transported primarily by strong winds and hence can be regarded as a proxy for eolian activity.4.The regional eolian activity was strong during the periods AD 950 to 1350and AD 1800 to²000.In addition,the most intensive eolian activity occurred at the Medieval Warm Period?MWP,AD 950 to 1350?,whereas the eolian activity was weak during the Little Ice Age?LIA,AD 1350 to 1800?.5.The history of eolian activity in Jili Lake Basin apparently show an opposite pattern to that recorded by Aral sea,Sugan Lake,and the Dunde ice cores,which may suggest a spatial differentiation of eolian activity.Changes in intensity and extent of the Siberian high and its interactions to other climatic sub-systems?e.g.the North Atlantic Oscillation?may have largely contributed to the spatial differentiation of eolian activity within the arid region of the central Asia.