An N-alkanes Perspective On The LGM Environmental Change In The Lake Fuxian

Since the Last Glacial Maximum,the climate of the Earth has undergone rapid changes of warming and cooling.It is particularly important to explore the environmental evolution under such unstable climate conditions for predicting in the future under the background of global warming.The monsoon climate in China is remarkable,their strength and retreat have a profound impact on the human in the region.Especially,the southwestern China is dominated by the Indian summer monsoon,which has developed a large number of plateau lakes.One of those lakes is Lake Fuxian.Here,the 9 m sediment cores from the deep-water area of Fuxian Lakewere detected and analyzed,such as n-alkanes,TOC,TN,and element contents,to reconstruct the environmental change since the Last Glacial Maximum.The driving mechanism was explored as well by comparing the regional climate records.The main conclusions were obtained as follows:(1)The n-C₂₃/n-C₃₁ ratio and Paq value of n-alkanes can further indicate the change of lake water level by indicating the variation of endogenous submerged plant input in the Sediments of Fuxian Lake.TOC content in lake sediments is related to environmental changes in the basin.The Rb/Sr ratio of core sediments indicates the intensity of weathering in the basin.The change of Fe content can indirectly reflect the change of lake water level by indicating the redox state of the lake.Ca element is mainly derived from authigenic carbonate in Fuxian Lake,which can roughly reflect the variation of temperature and lake productivity.(2)Environmental changes in the Fuxian Lake basin since the the Last Glacial Maximum have undergoe three periods and six stages.Three major periods:the Last Glacial Maximum(26-17.7 cal kyr BP),when the basin environment was dry and cold;the Last Deglaciation(17.7-11.8 cal kyr BP),when the basin environment showed slight signs of warming;the Holocene(11.8 cal kyr BP to the present),when the basin environment changed from warm and humid in the early to middle Holocene to dry and cool in the late Holocene.Six stages:Stage I(26-22.7 cal kyr BP),when the water level and temperature of Fuxian Lake were relatively low,and the climate was cold and dry.Stage?(22.7-17.7 cal kyr BP),the water level and temperature of Fuxian Lake were relatively low,and the n-alkane index indicates that the water level of the lake has dropped to the lowest,which was the driest and coldest period of the Last Glacial Maximum and the lowest water level.Stage III(17.7-11.8 cal kyr BP),the water level,humidity and temperature of Fuxian Lake are all on the rise.Stage IV(11.8-6 cal kyr BP),the water level is relatively high,but the temperature does not rise to the maximum.Stage V(6-3 cal kyr BP),the water level and humidity decreased slightly,but the temperature increased to the maximum.Stage VI(3 cal kyr BP to present),water level and temperature further decreased,and the basin environment gradually became colder and drier.The fluctuation of the environmental indicators since 2 cal kyr BP indicates the presence of human activities in the watershed.(3)Climate change in study areahas undergone several rapid climate change events since the Last Glacial Maximum.Firstly,the first warming during the Last Deglaciation period occurs at 17±0.5 cal kyr BP,which is earlier than the first enhancement in the East Asian monsoon region(14.5 cal kyr BP).Secondly,the YD event was recorded in Fuxian Lake around 12.8-11.8 cal kyr BP.Furthermore,different records in southwesten China regions responded the YD event at a different scale.and Finally,the Holocene seems have a typical climate characteristics that is decoupling precipitation and temperature in the southwest China.(4)Environmental reconstruction in the Fuxian Lake generally responds to solar radiation at low latitudes,especially,the holocene.The time point and amplitude of the rapid climate change events in the region since the LGM might be driven by the superposition of solar radiation at low latitudes and the variation of ice mass at high latitudes.In addition,clouds and topography may exert certain influence on it.