Characteristics Of Physical And Chemical Indicators Of Sediments In Peiku Co In Southern Tibet And Their Environmental Significanc

Climate change in the past two millennia is the core research content of two international large-scale projects,the"Past Climate Change Research Program"（IGBP-PAGES）and the"Climate Variability and Predictability Research"（CLIVAR）.Resolution sequences have important scientific and practical significance.Lake sediments are ideal carriers for studying paleoclimate changes.In the Tibetan Plateau,studies on the reconstruction of regional paleoclimate and paleoenvironmental changes using lake sediments have matured,but there are still relatively few studies on lake sediments in southern Tibet.Studies have not yet been reported.In this paper,the AMS¹⁴C dating technique is used to establish the age frame of PKC-2（83cm）from the lake sediment core PKC-1（62.5cm）in the southern Tibetan Plateau;Based on the analysis of the characteristics,combined with the lake area of Peikuco extracted from remote sensing images in the past 30 years,the potential relationship between the lake sedimentary record and the lake area was explored;the sediment elements and chromaticity of the lake sediment core PKC-3（98cm）were used,magnetic susceptibility were comprehensively analyzed,and an in-depth study was carried out on the evolution process of the climate and environment recorded by the Peikuco deposits in the past 2,000 years.The main research results of this paper are summarized as follows:（1）When the PKC-3 core was analyzed by XRF scanning technology,12 elements including Al,Si,S,K,Ca,Ti,Cl,Rb,Sr,Zr,P and Fe were extracted.Through principal component analysis and correlation analysis,it is found that the first principal component（PC1）can reflect the degree of weathering and erosion in the lake area,and then indicate the precipitation of the watershed.Among them,the ratio of Rb/Sr can reflect the input of coarse-grained terrigenous clastic materials;the ratio of Ca/Ti indicates the change of authigenic carbonate content in lakes;the ratio of Fe/Ti can indicate the change of grain size in sediments;and the ratio of Rb/Zr It may reflect the intensity of chemical weathering in the lake area.（2）The high value of redness（a*）of sedimentary cores in this study may correspond to the cold and wet climate configuration in the watershed,while the low value corresponds to the warm and dry climate.The change trend of magnetic susceptibility is very similar to the change trend of redness（a*）in chromaticity,and the correlation coefficient is high.Therefore,it is considered that the magnetic susceptibility can also reflect the dry and wet conditions of the climate to a certain extent.（3）Through the analysis of the carbon and oxygen isotopes and particle size changes of the authigenic carbonate of PKC-1（62.5 cm）,combined with the research on the change of the lake area in the past 30 years,it was found that the carbon and oxygen isotopes and the particle size（sand）are all in a certain degree in response to changes in lake area.The change characteristics of total organic carbon showed that the lake productivity in Peikuco was low,and the change characteristics of organic carbon isotopes showed that the plant types in the Peikuco watershed were mainly C₃ plants.（4）Reconstructed the paleoenvironment and paleoclimate change process of the Peikuco lake area in the past 2,000 years.Specifically,it is divided into five stages:stage I,100 a BC to AD 600 a,the climate is cold and wet;stage II,AD 600 a to AD 1500 a,the climate is generally warm and dry;stage III,AD 1500 a to AD 1900 a,the climate is cold and humid;stage IV,AD1900 a to present,the climate is warm and dry.In the past 2,000 years,the Peikuco Lake area has generally shown the characteristics of alternating cold and wet-warm and dry climate configurations.The paleoclimate changes in the past 2000 years recorded by the sediments of the Peikuco lake are basically consistent with the sedimentary records of the adjacent area Yamzhog Yumco,and also present the climate characteristics of alternating cold and wet-warm and dry.In addition,The stalagmite records in Bengle Cave in the southeast of the Tibetan Plateau are in good comparability with the climate change in the past 2000 years reflected in Peikuco.However,the history of monsoon activity recorded by stalagmites in Wanxiang Cave in Gansu Province on the northeastern margin of the Tibetan Plateau is quite different from the climate change in southern Tibetan.This shows that there may be significant differences in the climate evolution history and change mechanism between the southern Tibetan Plateau and the northeastern region.