Environment And C Limate Evolution Recorded In Sediment Of Hulun Lake Since Middle-late Holocene

Lake is occurred in a certain geological and geographical environment.It links to atmosphere,lithosphere,biosphere and hydrosphere,and not only provides abundant fresh water resources for human life,and also plays a good regulatory role on regional climate.Meanwhile,lake is the "source" and "sink" of matter in the region.Lake sediments is a good information carrier material for studying climate change and environmental evolution,which has strong continuity and rich environmental information with longer history and larger spatial scale.The environmental change rules in present and history could be inferred,and then the future climate change could be predicted by obtaining environmental information from the lake sediments.Hulun lake is a typical lake in the monsoon marginal zone in northern China.This zone is the west wind currents extending to the east and meeting with the east Asian monsoon,and which is controlled by east Asian monsoon,the west wind circulation and Siberia-Mongolian high pressur.Hence,the region is sensitive response to climate and environment,and is significant for the research of paleoclimate and paleoenvironment.A 100cm long sediment core is sampled at the north part of Hulun lake in March 2015.AMS14C,Grain-size,Total organic carbon(TOC),Total nitrogen(TN),Total phosphorus(TP),?13C,?15N and typical metallic elements are measured and analyzed,.The Paleoprocluctivity,the watershed of weathering degree and the change of lake water level are analyzed the environment and climate evolution of Hulun lake basin are reconstructed since middle-late Holocene(5400cal.a BP).The conclusions are:(1)Grain size frequency curves show two forms:unimodal and bimodal,which indicate the source is relatively simple.There are two sensitive components are extracted by Particle size-standard deviation method,and the component 1 is<8.71?m,component 2 is 8.71?158.49?m.Component 1 reflects the distances from the central area to sample site.Component 2 is of the properties of silt and sand particles dute to the wind weathering.The variation trends of the component 1 and 2 are opposite with each other,which reflects the lake sediment is water and wind weathering alternative by runs.(2)Paleoproductivity of Hulun lake varies from58.26-58.26 gCm-2a-1,with a mean of 104.09 gCm-2a-1.The trend of the paleoproductivity is gradual increasing and reached the maximum of 136.93 gCm-2a-1 in Holocene medium-term(5400?3480 cal.a BP),which shows the climate is warm and wet,primary productivity level is higher.The trends of the paleoproductivity is fluctuations,decreasing and then increasing in Late Holocene(348-?Ocal.aBP).Paleoproductivity,813C and TOC are gradually increasing in 195?0 cal.a BP,which indicates the dry climate and dry environment.(3)During the middle-late Holocene,the weathering of Hulun Lake basin is weak.The evolutions of environment and climate have undergone four stages,i.e.warm wet(5400?3202cal.a BP)?person(3202?655cal.a BP)?cold wet(655?179cal.a BP)?dry(179?0 cal.a BP).The water level of the lake fluctuates as following stages:high water level(5400?5144 cal.a BP)?low water level(5144?4477cal.a BP)?high water level(4477?1375 cal.a BP)?low water level(1375?449 cal.a BP)?high water level(449?226 cal.a BP)?low water level(226?0 cal.a BP).(4)The sediments of Hulun lake basin are response to the dry and cold events of 4.2 ka,The medieval warm period(MWP)is 670?1200 cal.a BP(670?1280 AD),the duration of the MWP is longer than eastern China(800?1100 AD)and shorter than western region MWP(500?1500 AD).The starting and ending time is 170?670cal.a BP,which is 1280?1280 AD,and it lasts for up to 500 a.(5)There obviously exist the 250a and 500a periodic signals in the climate variation processes of Hulun lake basin since middle-late Holocene,and 250a signal period is predominant.The climate cycling characteristics of Hulun lake Basin are mainly in a century scale.