Climate Change Since The Last Glacial Maximum Recorded By Lake Balikun In Eastern Xinjiang

Mid-latitude arid central Asia is one of the main resource areas of global aeolian dust which play an important role in the global climate system and ecosystem.High-resolution,absolutely-dated quantitative climate proxy reconstruction should present the climate change well in mid-latitude arid central Asia,to understand how to respond to the climate change in low-latitude and high-latitude area.It is important to understand mechanisms of climate and precipitation changes here,as water availability and deteriorated ecosystem in the region is crucial today and in the future.The arid northwest China,an important part of arid central Asia,is dominated by the Westerlies and Siberian High at present.Our study area,Balikun Lake,located in the center of the arid northwest China,and it is well site to study the climate change in the arid northwest China.A 62.53 m lake sediment core(BLK11A)was taken in the Balikun Lake center in 2011 in eastern Xinjiang.The top 6.8 m sediment core was subsampled by 1 cm interval in the lab for LOI and soluble salt content analyze,and the age model was defined by AMS 14C dating.135 samples from different depth were measured for LCAs and n-fatty acid carbon and hydrogen isotope to reconstruct pelao-tempeature and hydrologic evolution.We drew the following conclusions:1.LCAs distributions and calibration between U37k and water temperatureWe found LCAs in 12 of the 29 lake surface sediments from northwestern China.C37-C38 LCAs were detected in low salinity lakes,while C37-C42 LCAs were detected in saline and hyper-saline lakes.Analysis of the alkenone fractions using GC-MS showed that odd and even carbon number alkenones were methyl and ethyl ketones,respectively.The longest chain(C41-C42)LCAs only produced by phylotypes capable of growing in hyper-saline environments.Therefore,the presence C41-C42 alkenones is an indication of hypersaline environments.We did not find the relationship between salinity and%C37:4,%C38:4 based on our sediment samples and other published results.Based on water filter samples,there is well relationship between U37k and water temperature(y=0.016x-0.696,R2 = 0.64),but U37k' not.2.The water temperature reconstruction since the Last Glacial Maximum in Balikun LakeThere are two kinds LCAs distributions in the sediment indicating different LCAs producers in the sediment core.One is same to the species living the modern Balikun Lake,and using our calibration to calculate the temperature;the other species living relative low salinity environment,and we used four similar species' calibrations(Hap B:T= 35.84�/kU37k + 21.11;C.lamellose:T= 26.53�U37k + 15.89;P.paradoxa:T= 44.25�U37k+ 22.78)to calculate the temperature.We used the average value,and the mix value and max value is the error range.During LGM(25-19 cal.ka BP),the summer water temperature was low with a range of 6.3-18.1? and the average value is 12.9?.The summer water temperature showed a decreased trend during 25-20.8 cal.ka BP,and the average value is 15.3?.During the coldest period in LGM(20.8-19 cal.ka BP),the average water temperature is 10.5�C,cooled by approximately 7.4? than today.During 19-18 cal.ka BP,water temperature increased 4?.After that,the summer temperature was stable and low;the average value was 11.6?,cooled by approximately 6.3? than today during the Oldest Dryas.Around 15 cal.ka BP,the summer water temperature increased about 3?.The warming temperature was closed to the modern temperature between 14.9 to 11.7 cal.ka BP.Two cold events centered at 13.1-12.8 cal.ka BP and 12.1-11.8 cal.ka BP,cooled by approximately 3.3 and 2.6? than today,possibly correspond to the Older Dryas and Younger Dryas.The mean summer water temperature(about 16.8?)was closed to modern during 11.7-9.8 cal.ka BP,followed by cooling of approximately 3.2? that occurred between 8 and 9.8 cal.ka BP.After 8 cal.ka BP,summer water temperature rapidly increases(about 11.5v)to the peak warming in a short time(-150 years),with approximately 60C warmer than today during 8-6 cal.ka BP.It was a cooling trend during mid-Holocene(8-4.8 cal.ka BP)at the speed of 1.9?/ka and the general trend is punctuated by a cold event at 3.8-4.8 cal.ka BP.During the cold event,the average summer water temperature was about 14.9?(changing from 10.1 to 22.2?),cooled by approximately 3? than today.After 3.8 cal.ka BP,it was a cooling trend at the speed of 1.1?/ka,and the summer water temperature changed from18.3 to 22.8?.3.Lake level and salinity change in Balikun Lake since the Last Glacial MaximumThe lake level was low,even seasonally dry-up during the LGM,the last deglaciation and early Holocene in Balikun Lake.The lake level was relative higher during 19-18 cal.ka BP and 14.9-13 cal.ka BP.The salinity showed an increasing trend,and the lowest salinity in the LGM and relative high salinity in the last deglaciation and early Holocene.It was high lake level during 8-6 cal.ka BP,but the salinity didn't show obvious decreased.After 6 cal.ka BP,the lake level decreased,and the salinity increased and Balikun Lake became hype-saline lake.4.The climate and environment change since Last Glacial Maximum recorded by Lake Balikun(1)During the LGM,the climate was coldest and driest.Under the climate conditions,land vegetation was sparse and it was low lake level and low lake primary productivity.Heavy ?D of C28 n-fatty acids from aquatic plant indicated the heavy 8D of lake water and low precipitation,and lake water renew was slow.Low temperature leaded to low evaporation,which caused to the low salinity during LGM.The low salinity and low lake level were good for lots of Ruppia maritime growing in the lake.(2)During the last deglaciation,the summer water temperature and lake level showed millennial-scale variations,but the moisture or precipitation didn't show millennial-scale variations.The salinity increased,the lake primary productivity and the vegetation were sparse,which indicated a dry climate during the last deglaciation.During 15-11.7 cal.ka BP,the salinity increased,and Ruppia maritime didn't not grow in the lake.The ?13C of C2? n-fatty acid from land plants indicated the ratio of C3 plants was high,and the light 8D of C28 n-fatty acids indicated land plants using melt-water from the mountain,and the summer precipitation was low in the basin.(3)During early Holocene,the climate was relative cold-dry,and 813C and 8D of C28 n-fatty acids indicated the climate and vegetation(C3 and C4)frequency changed under unstable atmosphere circulation.Meantime,it was low lake level and low lake primary production and high salinity.After 8 cal.ka BP,the climate became warm and wet,high lake level and high lake primary production.The Holocene optimum period is during 8-6 cal.ka BP.The ratio of C4 plant was high,and the summer precipitation was main source for plants growing in the basin.After 6 cal.ka BP,the summer water temperature decreased and the climate became drier,the lake become hype-saline lake and the lake level decreased.During 6-4 cal.ka BP,the ratio of C4 plant was high,and after 4 cal.ka BP,the percentage of C3 plants increased.There is a cold dry event at 3.8-4.8 cal.ka BP.