Reconstruction Of Paleoenvironment And Paleoclimate In The Southeast Margin Of The Tibet Plateau Since 5000 Cal A B.P. By Pollen Date Of Lake

We selected chosed Shadzo Lake(the altitude is 4446 m)in the west of ZheDuoShan of the southwest monsoon region as study object which is located in the southeast margin of The Tibet Plateau of kangding in Sichuan province and which is very sensitive to climate change.Then we took 121 cm sediment core from the middle of Shadzo Lake,and the age?depth mode of the Shadzo Lake core was established by 210Pb and 137Cs dates of surface core and 3 AMS 14C dates.Based on the analysis of surface pollen around the Shadzo Lake,we constructed and discussed paleovevegetation and paleoclimate changes during the past 5000 years by the pollen date,carbon,TOC,TN,magnetic susceptibility,element at all.The results show that the paleovegetation and paleoclimate of this area can be divided into 7 stages during the past 5000 years as follows:In the period of 5040?4500 cal a B.P.,at the lower altitude mountainous region around Shadzo Lake,there distributed a certain area of coniferous forest dominated with pinus forests and there also distributed a few of picea/abies,tsuga.Secondly,there distributed a certain area of evergreen broadleaved forest dominated with evergreen oaks forest above the pinus forests.There is aslo a certain area of herbs around Shadzo lake,so climate was warm and wet;In the period of 4500?2640cal.cal a B.P.,the number of pinus trees and evergreen oaks trees decrease,but the number of herbs increase,so the temperature and humidity all decrease;In the period of 2640?2290 cal a B.P.,the number of pinus forests increase,but the area of evergreen oaks forests and the number of herbs all decrease,so the temperature and humidity is the highest during the past 5000 years;In the period of 2290?1620 cal a B.P.,the number of pinus forests decrease,but the area of evergreen oaks forests and herbs all increase,so the climate was cool and dry;In the period of 1620?660 cal a B.P.,the number of pinus forests increase,but the number of evergreen oaks forests and herbs all decrease,so the temperature and humidity a little increase;In the period of 1290?1940 AD,the number of pinus forests decrease,but the number of evergreen oaks forests and herbs all increase,so climate was cool and dry;After 1940 AD,the number of pinus trees increase but the area of evergreen oaks forests and herbs decrease,so the temperature and humidity all increase.Shadzo Lake recorded well some climatic events as the end time of "Holocene Optimum","Late Holocene","Medieval Warm Period","Little Ice Age" and "The 20th Century Warmig" in the sediment core.So,the paper is important to understand the changes of paleovegetation and paleoclimate in late Holocene in southwest China.