Study On Holocene Climate And Environmental Change And Human Activities In The Source Of Three Rivers

The Qinghai-Tibet Plateau is one of the most responsive regions to global climate change due to its unique alpine natural ecological environment,and is also the most important ecological security barrier in China and the Asian continent.The study of the relationship between climate environment evolution and human activities on the Qinghai-Tibet Plateau over long time scales is a hot scientific issue of current academic interest.The Sanjiangyuan region is located in the hinterland of the Qinghai-Tibet Plateau,with an average elevation above 4000 m.It is very sensitive to global climate change,and the study of the coupling relationship between the Holocene climate and human activities in this region is the key to the study of human adaptation to the plateau environment.Fossil spores play an important role in the reconstruction and study of paleoclimate and palaeoenvironment,and the type and number of fungal spores are good indicators of livestock activities,while the size and concentration of charcoal debris indicate the intensity of human activities to a certain extent.This paper uses fossil spore data to reconstruct the sequence of Holocene precipitation and temperature changes in the Sanjiangyuan area,and combine them with other environmental proxy indicators,livestock activity indicators and human activity indicators to reveal the relationship between environmental evolution and ancient human dispersal.In this paper,we collected two profiles in the Sanjiangyuan area,Lower Dawu and Zhongda,and identified 52 sporulation and charcoal debris samples in the Lower Dawu profile;81sporulation,charcoal debris and fungal spore samples and 60 total organic carbon(TOC)samples in the Zhongda profile.In the past five years,our team has found 61 human activity sites and collected 494 other human activity indicators in the field survey of Sanjiangyuan area.The fossil spore data were used to reconstruct the Holocene annual mean precipitation and temperature variation sequences in the Sanjiangyuan area to reveal the coupling process between climate change and human activities and their influence mechanisms.The main conclusions are as follows:(1)The early Holocene(11.5-10.5 ka B.P.)profiles have low spore concentrations,with A/C and TOC gradually increasing.The reconstruction results show that precipitation and temperature fluctuated and increased in the Sanjiangyuan area,and the total fungal spore concentration was low,while the charcoal dust concentration in the Zhongda profile reached a high value,indicating that human activities had set foot in the Tongtian River basin in the Sanjiangyuan area.(2)The sporulation concentration and A/C ratio of both profiles reached maximum values in the middle Holocene(10.5-5.0 ka B.P.),and the sporulation content of tree and shrub species increased significantly;the reconstruction results show that precipitation and temperature in the Sanjiangyuan area reached their peak at this stage.Fungal spore concentrations increased,as did the levels of Sordaria spp and Glomus spp,fungal spores indicative of grazing and human activity,suggesting that there may have been human activity by early domesticated animals.(3)Sporulation concentration values are higher in both profiles from the Late Holocene(since 5.0 ka B.P.),and A/C ratios have decreased relative to the Middle Holocene,a period of significant climatic fluctuation.Human activity increased significantly during this period,and the concentration of faecal fungal spores in the profiles reached a maximum,indicating more extensive livestock activities.