| TThe Dawa Mountain of Sichuan province belongs to the subtropical monsoon climate zone,located in the upper reaches of the Yangtze River and the southeastern edge of the Tibet Plateau,China.Dawa Mountain peatland in the transition zone between the Sichuan Basin and Tibet Plateau.As one of the few peat sediments that span the Last Glacial Maximum(LGM),which provides a valuable material for high resolution studies of paleovegetation,paleoenvironmental evolution and paleoclimatic driving mechanism.The chronostratigraphic framework of this peat core was based on 11 AMS radiocarbon dating method.In this study,pollen data used as the main proxy of environment and climate,grain size analysis and geochemistry were also applied for verification and comparison.This allows us to probe into the variation of sediment environment,and our work expected to shed light on the relationship among different climate factors,solar radiation and surface sea temperature(SST)of Arabian and the bay of Bengal.The results of pollen,grain size and geochemistry records in the core of the Dawa Mountain peatland were comprehensively comparison,and it was found that the change process of sedimentary environment reflected by different proxy in the core was consistent.The results show that Dawa Mountain peatland sedimentary environment experienced three main stages since the LGM: during the LGM period sedimentary environment should be a shallow lake,and transform from the shallow lake to peat in the Last Deglaciation,the Holocene sedimentary environment has evolved to peat entirely.Pollen spectrum shows that vegetation of the study area was dominated by trees and shrubs,herbs are relatively rare.According to the characteristics and changes of palynological assemblages in different periods,the vegetation evolution experienced four stages in this region: 25000～18200 cal a BP(LGM),Betula,evergreen sclerophyllous oaks and temperate coniferous was most abundant at first,which reflects a landscape of a aconiferous-broadleaved or evergreen-broadleaved mixed forest.However,the pollen concentration was noticeably low,and plant genera were seldom;18200～11000 cal a BP(Last Deglaciation),the vegetation is mainly composed of Betula and temperate coniferous;11100～1000 cal a BP,subtropical evergreen broad-leaved became the dominated during the Holocene thermal maximum,accompanied by the appearance of some subtropical evergreen broad-leaved taxa such as Quercus(E),Castanopsis/Lithocarpus and Cyclobalanopsis.The climate became warm and wet;Human activities became more obvious after 1.0 ka with the expansion of the secondary forest(main Aluns),and the percentage of trees and shrubs pollen decreased,while the herbs pollen increased significantly.A Comprehensive comparison of palaeoclimate records in southwest China and other regions,we believe that the climatic records in Dawa Mountain since ～25 ka BP was consistent with the palaeoclimatic records of other lakes in southwest China.The climate change in Dawa Mountain area,especially the temperature change,was mainly controlled by the variation of solar radiation,the monsoon intensity in low-latitude and the regional Sea Surface Temperature(SST)since the LGM.At the same time,by comparing the temperature records in different monsoon regions,the results show that the first warming up was in the same time between the southwest monsoon region and the southeast monsoon region after the last glacial period,and the temperature change is both controlled by the variation of solar radiation. |
