Pollen Records From Northwest Yunnan Plateau And West Sichuan Mountain And Paleoclimate Significance Since Later Period Of The Late Pleistocene

To reveal the truth and find the laws of the Paleoclimate change since the Last Glacial is of great significance for mankind to respond the climate change in the future. thus, the research on the climatic and environmental changes of that period receives much concern. The uplift of Qinghai-Tibetan Plateau and Yunnan-Guizhou plateau possesses profound significance for Paleoclimate and Paleoenvironment. Besides, there are many researches and works in the Paleoclimate and Paleoenvironment of the large section of the East Side of Qinghai-Tibetan Plateau and Yunnan-Guizhou plateau. Significant conclusions were drawn by previous researchers who took their pollenspore research in the Heqing region, Yunan province,and Ruoergai plateau, Sichuan province, however, these researches were somewhat limited:the Temporal Scale was large; the conclusions was comparable in a large scale but made a great difference in the details; the qualitative analysis were often used; the time scale were different. Therefore, it was difficult to make a comparative analysis and to draw consistent conclusions on paleoclimate regional characteristics in this area.In this study, even though Shangrila and Hongya where the sampling spots were arranged were not far apart, they had different Geomorphological types, that is to say, Shangrila is in the Plateau region in the northwest of Yunnan province, Hongya is in the Mountainous regions in Western Sichuan. Whether the pollen record in the two sampling spots varies by geomorphic feature? Can they form regional characteristics with those of surrounding areas? Shangrila, Hongya, Hulu Cave and Dongge cave locate in the subtropical region and the modern climate in these areas shows obvious monsoon climate characteristic. The main differences between them are geomorphological types and the distance from sea. Then, What will the pollen record and stalagmite records be different? And how will the global and hemisphere events (such as Heinrich events, BA events, Younger Dryas Events,8.2kaBP cold events, Medieval Warm Period, Little Ice Age)influence on the pollen record and whether can we find the evidence from the pollen record? The questions mentioned above are the main problems that this research wants to solve. This research established a chronological framework of YXL section in Shangrila, Yunnan province since the later period of late Pleistocene by AMS-14C. In this research, the conventional acid-alkali method to treat the sample, heavy liquid and sieve cloth to extract Strata pollen were used. The researcher identified pollen by using of Luopacias index system, and established the pollen record of YXL section and SHG section. The researcher used ecological structure characters of pollen assemblage and their changes to deduce the climate changes in Shangrila area, Yunnan province and Hongya area,Sichuan province since the later period of Late Pleistocene. The researcher used Paleoclimate parameter method to reconstruct the paleotemperature changes and Paleoprecipitation change sequence since35670cal.yr BP. The researcher compared the pollen record between the two areas and investigates the similarities and differences between them. The researcher compared the pollen records and stalagmite records between the two area and those of surrounding areas. The researcher analyzed the relation and difference between them. The conclusions are as follows:Shangrila areas has experienced such process of Paleoclimate change:moderate and a little dry-cold and dry-slightly warmer and wetter-cold and dry-warmer and wetter-cold and dry-warm and wet-moderate and a little dry-cool and a little dry from about31570cal. Yr BP and there are some reversals in the process; Hongya areas has experienced such process of Paleoclimate change: warm and wet-moderate and moist-cool and dry-moderate and moist-cold and dry-moderate and moist-cool and moist-warm and wet-moderate and moist from about35670cal. Yr BP and there are some reversals in the process.To compare the YXL pollen record and the stalagmite record of Hulu cave, this research found: the cold-dry climate in plateau area which was caused by cold-dry climate events had longer duration than cold-dry climate events itself. The reasons were the follows:the underlying surface of snow-ice covering in plateau area had strong cooling effect and the positive feedback effect caused by the cooling effect would accelerate the decrease of temperature. As long as climate turned to be warming, the ice-melting needs a huge amount of thermal energy, so the temperature and humidity change would be relatively backward.According to the Comparative study of YXL pollen record and SHG pollen record, this study found the records from the two areas are comparable on the whole:the paleoclimate evolvement trends of the two areas were also similar since31570cal.yr BP. The main difference of paleoclimatic evolution between the two areas was that the climate fluctuation characteristics of YXL pollen records was much obvious than that of SHG pollen record. This is caused by the fragile natural ecological environment in plateau area.