Climatic And Environmental Change History In The Western Tibetan Plateau During The Holocene, Recorded By Lake Sediments From Aweng Co

Asian summer monsoon(ASM)evolution history on the Tibetan Plateau(TP)is crucial scientific issues in paleoclimate studies.The researches on how and to which extent ASM influenced the TP during the Holocene are mostly conducted at the modern ASM margin on the northeastern TP and southern TP.Such researches,however,were rarely carried out on the western TP.Therefore,more high-resolution records with reliable chronology are necessary in the western TP for comprehensive understanding of the ASM evolution history and the interplay history between the ASM and the westerlies during the Holocene on the TP.An alpine lake sediment from Aweng Co,which is located in the western TP,was chosen in this project to reconstruct the paleoclimate and paleoenvironmental change in the western TP based on the accelerator mass spectrometry(AMS)¹⁴C dating,multiple proxies with specific meanings(including ostracod shell and carbonate isotopes,organic carbon isotope,trace elements and pigment)and studies on the modern water,soil and plants samples in the catchment.On the basis of the previous studies,we tentatively discuss the scope that ASM influenced during the Holocene on the TP and the possible mechanisms.The main conclusions are as follows:(1)The climate change in the western TP during the Holocene was mainly driven by the Indian summer monsoon(ISM)variations,and the terrestrial and aquatic ecosystems were highly sensitive to the climate change.During 10.6⁷.2 Cal ka BP,the ISM was on its maximum intensity and the climate was wet.Meanwhile,terrestrial plants in the catchment were productive and the biomass of algae was high.From 7.2to 5.1 Cal ka BP the climate was moderate(still wet,but drier than before),causing decreased terrestrial plant cover the lowered algal productivity.Between 5.1 and 2.9Cal ka BP,the climate became even drier,dolomite precipitated in the lake water because of the high Mg/Ca ratios induced by a dry event between 4 and 2.9 Cal ka BP.After 2.9 Cal ka BP,the ISM intensity was minimum,leading to the driest climate and lowest lake level since the early Holocene.The algae productivity was high in this phase.(2)The climate reconstructed from Aweng Co lake sediment revealed that the climate in the past 2000 years on the western TP was consistent with the typical climatic characteristics(warm-wet and cold-dry regime)in the region controlled by ISM.EI Nino-Southern oscillation(ENSO)is one of the factors that controlled the climate in the western TP during the past 2000 years.(3)The impact of the global warming on the lake ecosystem variations.On the background of the global warming,the ice melt much quicker than before and plenty of glacier melt water fed the lake,resulting in dramatic expansion of lake area.In addition,the aquatic plant productivity decreased and the increased temperature accelerated the decomposition of the organic matters,leading to the decreasing of the organic matter buried rate.