Characteristics Of Organic Biomarkers In Surface Sediments Of The Northern Tibetan Plateau And Its Environmental Significance

Biomarker compounds from organic matter in lakes is a clear indicator of organic matter sources,such as vegetation types and paleoclimate characteristics.However,due to the source of organic matter in lake sediments is complex,and the influence of organic matter in early diagenesis and other factors,the research process of using modern significance for its environment is the basis of understanding of this index.Qinghai Tibet Plateau is located in the southwest plateau Chinese,there are many lakes in different chemical properties,but the influence of human activity is very weak,and the vegetation is also very simple,so lakes are the favorable area to indicate the process of modern environment by biomarkers.In this paper,using gas chromatography-mass spectrum technique,organic matters of lake sediments in different lakes in northern Tibetan Plateau were extracted and separated.Biomarkers including n-alkanes and sterols,which indicate the source of sediments,were detected out.According to the distribution characteristics of n-alkanes and sterols compound composition in sediments,and we discussed the sources of organic matter in lake sediments by using the n-alkanes index,for example CPI,ACL,Paq,C27/C31,nC21~-/ nC22~+,nC17/nC31 and(nC15+nC17+nC19)/(nC27+nC29+nC31).We got the results in below.(1)In the study area,almost all the lake sediments have the input of terrigenous higher vegetation,but their abundance is different.Almost most of the lakes have aquatic organism.Biological source of sediments which collected from the middle east lake of the northern plateau mainly comes from the contribution of terrigenous higher vegetation,small part is terrestrial mixed with aquatic vegetation;and the biological source of sediments in northwest lakes is mainly aquatic organisms,mixed with a small amount of higher vegetation.In the same lake,there are differences in the distribution characteristics of n-alkanes in different locations,which can be used to reflect the differences and changes in the ecological environment of lakes.(2)In the study area,a large number of steroids and steroids were detected in all the lakes,and the carbon number distribution is mainly concentrated in the range of C27 to C29,and the double bond position of steroids is between 5 and 22 carbon.Detection of steroid enol indicates that 24-ethyl cholesteric-5-enol and 24-ethyl cholesteric-5,22-two enol which is higher content of organic matter in higher plants,is predominantly in the northern Tibetan Plateau Lakes in east central;but the abundance which come from many phytoplankton,such as the main component of diatom 24-methyl cholesteric-5,22-two enol and 24-methyl cholesteric-5-enol,is relatively high in the lake in the northwest of the northern plateau.(3)For closed lakes,the analysis of n-alkane index and even carbon advantage distribution characteristics,and combing with the lake salinity indicates that the middle east of the northern Tibet Plateau is warm and wet,comparing to the cold and dry environment in the northwest of the Plateau.