A Preliminary Study On The Vegetation And Climate Changes During 19.9-5.0 KaBP In The Middle-upriver Zuli River, Western Loess Plateau

This paper discussed the reconstruction of the history of the vegetation and climate changes in the middle- upriver Zuli River during 19.9-5.0 KaBP period, according to the environmental and climatic indexes of pollen, granularity and organic carbon etc., based on the analysis of pollen absolute concentration, pollen percentage concentration and principal components analysis (PCA) of pollen, and Median diameter Grain(Md) analysis and Total Organic Carbon (TOC) analysis and the following conclusions were drawn:During the period of 19.9-15.4 KaBP (Last Glacial Later Period), the climate was cold. During the forepart of this period, especially in the upriver mountains, spruce (Picea) conifer forests were well developed and the climate was relatively cold and humid; during the later period, spruce (Picea) forest in the upriver mountains might degrade or even disappear while Pine forest extended gradually, in the arid area appeared steppe vegetation under a relatively cold and dry climate. Between these two periods appeared two relatively distinct humid climate stages. Around 15.4-11.0 KaBP (Last Deglacial ), the coverage of the vegetation were in better condition and the climate fluctuated tempestuously. In the upper mountains vegetation was dominated by Pine forest with open broad leaves forest appeared partly and the area of the steppe enlarged. At the same time there existed two warm and humid climate periods and two dry and cold climate periods corresponding with B0lling and Aller0d Events and Old Dryas and Younger Dryas Events. Druing 11.05-5.0 KaBP (Early-Mid Holocene) the climate was warm and humid and fluctuated frequently and tempestuously. The vegetation mainly dominated by Pine forest, broadleaves forest had an obvious extension; shrubs and herbs were well developed. It appeared as forest steppe vegetation which was dominated by coniferous-broad leaved mixed forests. After 7.2 KaBP climate tended to be cold and dry according to the trends.In study area, during the 19.9-5.0 KaBP period, climate showed a series of change: cold humid-cold dry-warm dry-warm humid. The trends of the climatic changes and the climate events had good coherence with records of global climate changes, especially the trend of climate changes suggested by XiaoGou profile during Last Glacial Later Period-Last Interglacial-Holocene period was mostly the same as the one showed by records of Greenland Ice Core and Guliya Ice Core. This indicated that the climate changes in study area are controlled by global climate factors. The characters of the climate and vegetation alternation reflected that during 19.9-5.0 Ka BP period the factors that influenced the climate system might be very complicated which indicated the complicated interactions between the Asian monsoon system and westerly currents. The further study on the climatic mechanical alternation is required in this area.