The Study Of 7380 Years Environmental Change Of The Easthern Oinghai-Tibet Plateau In Hongyuan

Hongyuan peat,which is located at easten of Tibet plateau,Sichuan provience,is deeply influenced by Southwest Monsoon.After researched the loss on ignition(LOI),geochemical elements,concentration of total mercury and chromaticity index,we conclude that Hongyuan peat have a good capacity to show the climate change since 7380 yr BP.Different proxy index of Hongyuan peat showed Cold Events,when in 7200,6300,5200,4500,4200?4000,3400?3200 and 1800?1600 yr BP.It can be separate into four sections during 7380?2000 yr BP(1)7380?6500 yr BP,turns warmmer and wetter,have a big climate fluction;(2)6500?5100 yr BP,turns colder and drier,have a small climate fluction;(3)5100?4000 yr BP,keep turning colder and drier,have a obvious fluction;(4)4000?2000 yr BP,temperature is smooth and serady,humidity changed obviously.The REDFIT analysis of LOI and concentration of total mercury shows that there are 2500,1250,910,550,420,360,310,280,200,160,125 and 75 years cycles,which is similar as solar activity cycles,solar orbit cycles and Southwest Monsoon cycles.The solar radiation have a deep significant to the calefaction of Tibet plateau.At the same time,the calefaction of Tibet plateau have a big influence to the strength of monsoon.The variation rendency of LOI and concentration of total mercury have the same rhythm with the solar radiation changing.As same as the concentration of ?18O in the sedinebt of Indus river estuary,the Cold Events in Hongyuan peat,such as 7200,6800,5400,4600,4200,3300 and 2700 yr BP,happened with the reduce of solar radiation.The results shows that the solar radiation changing can do change the strength of the Southwest Monsoon.