The Precipitation Evolution Research Of The Peat In Caohai Region Of The Southwest China Since The Holocene

The Nantun peat is located in the northeast of Guizhou Province and the east of the Yungui Plateau,because of the the unique geographical location,it is affected by the influences of the southwest monsoon and the East Asian monsoon.Through the analyses of different proxy indexes(the total mercury content,ash content,geochemical elements and color ratio),the climate change of the Caohai region since 9445 cal yr BP can be clearly indicted.Combining with other regions' indexes,it is reflected that there are great differences in the response time and degree of the rapid climate change events in different regions during the Holocene.The total mercury content of the Nantun peat responsed to the Asian monsoon's intensity during the Holocene,and the intensity of the Asian monsoon weakened firstly,then increased and finally weakened.The total mercury content of the Nantun peat was affected by both the southwest monsoon and the East Asian monsoon,the influence degree of the southwest monsoon is obviously stronger than that of the East Asian monsoon.Owing to the thermal stability of mercury,the total mercury content of Nantun peat can used as an important indicator to reflect the changes in humidity,and it can be used as an effective exploration of the climate change in the transition zone affected by both the southwest monsoon and the East Asian monsoon.Based on the comprehensive analyses of multiple proxy indexes in Nantun peat during the Holocene,the climate change in Caohai region can be roughly divided into four stages:(1)From 9445 to 7050 yr BP,the climatic fluctuations were relatively moderate,gradually alleviated from cold-dry;(2)From 7050 to 4500 yr BP,the climate turned warm and wet,with the increased frequency and amplitude of fluctuations;(3)From 4500 to 2400 yr BP,the fluctuations intensed with warm-wet climate;(4)From 2400 to 470 yr BP,the climate gradually became cold-dry and the fluctuations were relatively gentle;In addition,the rapid cold-dry events occurred in the Caohai region during the Holocene were recorded in the multiple proxy indexes of Nantun peat,appeared respectively in 8200 yr BP,7000 yr BP,6500 yr BP,5000 yr BP,4200 yr BP,3800 yr BP,1900 yr BP,and 900 yr BP.The Caohai peat in transition zone was driven by the high and the low latitude factor(El Ni?o),and the influence of the high latitude drive is relatively small.Compared with the Hongyuan area,the influence drived by the low latitude in the Caohai area is weak.Using the power spectrum analysis and the wavelet analysis of the total mercury content and ash content of Nantun peat,the remarkable cycles of the climate in Caohai region are 2000 a,1087a,572 a,255a,214 a,and 89 a,which consisted with the cycle of solar activity and the ice debris events in the North Atlantic region,therefore it confimed that the solar activity is an important driver of climate change in the Caohai region.Therefore,the climate change in the southwest monsoon region during the Holocene is affected by the low latitude factor(El Ni?o)and solar activity.