Optical Dating Of One Episode Of High Lake Level Of Poyang Lake During The Late Quaternary

As the largest freshwater lake in China,Poyang Lake plays an important role in flood regulation,water conservation and biodiversity conservation.The lake is greatly influenced by the East Asian monsoon and which was sensitive to climate changes during the Late Quaternary.Previous studies on the water level of Poyang Lake mostly focus on the inter-annual observation of historical data.However,the Late Quaternary water level changes of Poyang Lake in a much longer time scale is still poorly understood.Especially,it is still unclear whether there were high lake level records in the area during the MIS3/MIS 5.This study attempts to take the Late Quaternary sediment profiles preserved around the Poyang Lake area as the research object,with OSL dating techniques,and other climate proxy indicators such as grain size,chromaticity,magnetic susceptibility and loss of ignition to study one episode of high water level of Poyang Lake during the Late Quaternary.The results were as following:?1?A¹1m thick Jishan profile was obtained and it can be further divided into 15alternating layers of aeolian sand layers,sandy soil layers,soil layers and lacustrine layers.The main grain size distribution of the profile is between 0.283²000?m,mainly composed of sand,with a small amount of silt and clay.The average particle size of the different layers is 2.39?,and the sorting property is poor.It is very positive and the peak is very sharp.The content of organic matter and carbonate is low as a whole.The peaks and valleys of chroma parameters changed obviously.Brightness index?L*?changed at a higher level,while redness?a*?and yellowness?b*?indexes changed at a lower level.The magnetic susceptibility fluctuates greatly in response to different stratigraphic layer.?2?The average particle size of the lacustrine layer is 5.49?.In the frequency distribution of the grain size,the skewness is nearly symmetrical,and the kurtosis is normal.Jumping and suspension components are the main components,and the frequency curve is a three-peak type,which is composed of multiple components superposed,it may be affected by the action of lake waves and wind.The organic matter content corresponds to the peak value of the profile;the carbonate content is low under the influence of leaching.The chromaticity characteristics are expressed as high brightness,low redness,and high yellowness.The lacustrine layer targeted is thought to be formed at the transition between lake shore and central lake and it is influenced of repeated modification and separation of water and air media,sedimentary hydrodynamics and weathering.The magnetic susceptibility value is very low,only 2.46×10-8m³g^-1,and the content of magnetic minerals is very poor.?3?The lake layer is about 33m above sea level,which is still about 10m higher than the historical maximum water level of Poyang Lake area of 22.53m,indicating that the Poyang Lake may have an extremely high lake surface in the Late Quaternary.OSL dating technology shows that the high lake level of Poyang Lake is formed in 56.3³7.2ka,corresponding to MIS 3 stage.Therefore,abundant precipitation,large-scale transgression,flooding of the Yangtze River and supporting action may be the important reasons for the extreme high lake surface of Poyang Lake.The formation of the high lake surface at this stage may be a response to global climate and environmental changes.