A Record Of Environmental Change Between18,000and14,000Calendar Years B.P. Indicated By Diatom Assemblages From Yunlongtianchi

A series of alternating cold and warm events has happened all over the world in the transition from the last Glacial to the last deglaciation. Among them cold event of Heinrich event as one of the most concerned events was the last Heinrich event during the transiation from glacial to interglacial.The high resolution also indicated that the Heinrich event show the East Asian monsoon also show abrupt change during last glacial, and there are many related research records. However, the record about Heinrich event in the region where are affected by southwest monsoon was lack so far. And it is not enough to adequate explanation for the problem.Here, we provide high resolution record of Heinrich events using the diatom as the indicator from Yunlongtianci lake, which affected by the Southwest monsoon.Diatoms with siliceous is preserved well in sediment and sensitive to environmental change. It can record the high-resolution paleoclimate history change. In particular, the relative abundance of planktonic diatoms and benthic diatoms in closed lakes is a sensitive indicator for the changes in lake water level. The chronology of the core from this lake is based on the linear interpolation of18reliable and the calibrated AMS14C dating.Based on the record of high-resolution diatom fossils from18.5ka to14.5ka B.P., the conclusions are as follows:1.31genus and241species are recognized. The main planktonic species include: Cyclotella psudostelligera, Cyclotella praetermissa, Cyclotella radiosa. The main benthic species include:Punctastriata pinnata, Staurosira construens f. construens, P. elliptica, Achnanthes saccula, Achnanthes subatomoides, Achnanthes minutissma and Navicula microdigitoradiata.2. We recognized three diatom zones based on the change characteristics of the diatom assemblage and the ratio of planktonic and benthic species, And analyzes the instructions environment significance which diatom indicates.3. From18.5ka to18ka B.P., main diatom fossils are benthic, indicating a low water level and a weak Southwest monsoon. From18ka to16.2ka B.P., planktonic diatom is dominant species, indicating a high water level and a strong southwest monsoon. From16.2ka to14.Ska B.P., benthic species dominate again, indicating a low water level in Yunlong Tianchi lake and a significantly weaking of Southwest monsoon.4. The significant H1events was recorded in Yunlong Tianchi Lake, and the result for the comparison of the isotopes record of NGRIP ice core and Hulu cave stalagmite with the diatom record shows very good. These data imply that climate and environment changes in this region were affacted by the Northern Hemisphere climate system.5. The analysis of diatoms biological diversity during the this period from Yunlong Tianchi Lake, indicating that the diversity of diatom was low during the18.5ka to18ka B.P.. The diatoms biological diversity increased rapidly during the18ka to16.2ka B.P. The diatoms biological diversity reduced rapidly during the16.2ka to14.5ka B. R.The biological diversity of Diatoms of Yunlongtianchi lake decreased when ecological environment change to complex, and it increased when ecological environment change to simple.The changes of the biological diversity of diatoms of the study area is closely related to the changes of the habitat of the lake.