A 3500 Year Climatic Changes Recorded By Sediment Of Tian'E Lake,Middle Of Qilian Mountain,China

Lake sediments have the features of wide distribution,high resolution,well continuity and sensitive response to climate changes,making it the irreplaceable advantages compared with other records in reconstructing climatic and environmental evolutions on all kinds of short time scales and different space dimensions.Lake sediments,especially the closed lake sediments in dry and hemi-dry inland can be used to record the changes of the continuous paleoclimate,which is one of the important archives of paleoclimate and global changes.Sediment core retrieved from Tian'E Lake?TE Lake?in the middle of Qilian Mountain was used to reconstruct climatic and environmental changes during the past 3500 year based on the analysis of total organic carbon?TOC?,carbonate content,mineral composition,elements and lithologic characters.The chronology of TEB core was established using AMS ¹⁴C dates of ten terrestrial plant residues.Preliminary results are as follows:?1?Through survey in lake basin and analysis of isotopes,the TE Lake is an alpine lake mainly supplied by underground water,and carbonate of lake is mainly derived from the lake basin calcareous rock.After genetic analysis the carbonate,we argue that the carbonate is mainly controlled by the change of groundwater recharge and can indicates dry and wet changes of the lake sediment environment and further reflects changes of local precipitation.According to multi-index comprehensive analysis of the TE Lake sediment core,sedimentary environment has experienced eight times of obvious changes in dry and wet since 3500 years.The wet period is respectively 1440to 1260 BC,1120 to 750 BC,750 to 120 BC,200 to 260 AD,690 to 720 AD,1300 to1330 AD,1300 to 1730 AD and 1850 to 1950 AD.Before the little ice age?LIA??1534BC¹300 AD?,the frequency and extent of peak values of carbonate content have the trend of reduction and decline in overall,reflecting a gradual reduction of lake precipitation.Especially during the period of medieval warm period?MWP??720¹300AD?,the climate is the most drought since 3500 years.The LIA started at 1300 AD and there were three periods of heavy precipitation in which the peak period of the LIA was during the period of 1600¹730 AD.Affected by the west wind circulation,TE Lake records the warm-dry and cold-wet climate model of MWP and LIA respectively.At the same time,the lake reflected a more unstable climate in LIA than MWP.?2?The modern surveying data shows that Fe element in lake sediments is correlated well to balance line of Qiyi Glacier from 1958 to 2008,reflecting that such weak migration element in lake sediments are probably influenced by fluctuations of the glacier.The glacier advance can cover partial weathering areas,putting less weak migration elements into the lake and the content of Fe decreases.Conversely,weathering source areas enlarge with the glacier retreat,adding more weak migration element into the lake.Fe element in TE Lake sediments is a good indicator of reflecting changes of the glacier,the 8-times low values of the Fe element recorded in TE Lake correspond to 8-times glacial advance respectively.At the same time,the period is corresponding to the humid period,which further reflects that the fluctuation of the Qiyi Glacier is mainly affected by the precipitation changes in the lake area.In addition,the content of Fe and the results of temperature reconstruction in the region,China and the northern hemisphere were compared,and it was believed that the Qiyi Glacier were controlled by the changes of temperature in a certain period.