Climatic Fluctuation Characteristics And Human Activities In Fuxian Lake Basin In The Past 3000 Years

Fuxian Lake is located in the middle of Yunnan Province.The regional climate is mainly affected by the southwest monsoon,and its unique natural geographical location makes it more sensitive to the response of climate environment,which is of great significance in the study of paleoclimate environment.It is of great significance in the study of paleoclimate environment.By analyzing the variation characteristics of environmental proxy changes in the sediments of Fuxian Lake,such as particle size,carbonate,element,mass susceptibility,total organic carbon?TOC?,total nitrogen?TN?,C/N ratio?C/N?,the high resolution AMS¹⁴C dating results and Morlet wavelet analysis,this paper comprehensively analyzed the characteristics and periods of climate evolution and human activity in Fuxian Lake Basin since 3000 years.On the basis of this,the driving mechanism of climate evolution in the basin is discussed.The results show that:1.Variation characteristics of environmental proxy indexes in Fuxian Lake sediments:Between 3000-2400cal a BP,the TOC,TN content and C/N ratio in the sediments of Fuxian Lake were in the high stage,the grain diameter<4um content and mass susceptibility were in the low stage,there is no coarse particle size substance in sediment?>64um?,and Zr content and Rb/Sr ratio were in the low area.The environmental proxy index of sediment?grain size,carbonate,element,mass susceptibility,TOC,TN,C/N ratio?indicates that the basin is in a relatively cold climate,the environmental changes are relatively stable,and the human activities are not significantly disturbed.Between 2400-1800cal a BP,the TOC,TN content and C/N ratio in the sediments of Fuxian Lake decreased obviously,the content of particle diameter<4um increased,the content of particle size>64um increased slightly,Zr content and Rb/Sr ratio increased.The proxy indexes?grain size,carbonate,element,mass susceptibility,TOC,TN,C/N ratio?of sediment indicate that the rapid change of environment in the basin.Since 1800cal a BP,the TOC,TN content and C/N ratio in the sediments of Fuxian Lake have gradually decreased in the fluctuation,and the content of grain size<4um increased in the fluctuation,Zr content and Rb/Sr have increased slightly in the fluctuation.The frequent fluctuation of sediment indexes?grain size,carbonate,element,mass susceptibility,TOC,TN,C/N ratio?indicates that the environmental change is very significant in the basin.2.The results of wavelet analysis of environmental substitution indexes of Fuxian Lake sediments:Since nearly 3000 years,there are obvious 1000a and 500a quasi-periodic signals in Fuxian Lake.There are 500a quasi-periodic signals in each substitution index,and the performance is obvious.In addition to C/N ratio,the1000a quasi-periodic signals exists in other indexes.3.The climate change in Yunnan is mainly affected by the southwest monsoon and the East Asian monsoon,and the process is more complicated.Through the comparison of environmental indicators of sediments in Fuxian Lake,the oxygen isotope of stalagmite in Donggedong,Guizhou Province,and the low latitude solar radiation,and the wavelet analysis results of the proxy indicators of various environments in Fuxian Lake found:The period of paleo-environmental climate change in Fuxian Lake has a good corresponding relationship with solar activity,which indicates that solar radiation plays a major role in climate change.4.Relationship between Climatic and Environmental Evolution and Human activities in Fuxian Lake Basin since 3000 years:From 2400 cal a BP,the environmental index records of sediments in Fuxian Lake show that obvious human activities have occurred in the basin,but the environmental change was mainly controlled by climate change.Since 1800 cal a BP,the influence of human activities on environmental change in Fuxian Lake basin has been strengthened obviously.As frequent human activities?such as cutting firewood and reclaiming farmland?in the region have increased soil erosion in the lake basin,resulting in large amounts of sediment into the lake,therefore,the continuous improvement of human activities is also recorded in the environmental proxy indicators of lake sediments.