Pollen Assemblage Features Of Tamarix Cone And Environment Changes In Lop Nur Region,xinjiang Province,china

Lop Nur region is located in Bayingolin Mongolian Prefecture of Xinjiang and the eastern part of the Tarim Basin which is a closed basin, the east, north and south sides of which are shielded by the mountains in this region. The region is in the depths of Landlocked hinterland of the Eurasian, far from the sea. The arid environment in the region restricted by the surrounding areas, has developed continually since Quaternary period, which is one of the famous arid areas in China and even all over the world. The region belongs to the extremely arid hungriness continental climate in warm variable zone with low rainfall, high evaporation, big temperature difference, strong winds and other characteristics of typical arid continental climate. In the region the winter is frigid and dry, and the summer is hot and little rain. In history, Lop Nur was the destination of every river in Tarim Basin and bred ancient civilization of the West Regions represented by Loulan. Environmental evolution of the Lop Nur region is the epitome reflecting on environmental change of the arid areas, focused by the researchers and the region is the hotspots of scientific exploration and observations. The research of environmental evolution in the region has an important reference value in global change research, ecological environment protection and resource development in arid desert.In the Lop Nur region, on both sides of river-banks, delta areas, ancient river-banks and local lowlands, Tamarix Cones distribute together. Tamarix Cone is a kind of shrub-coppice dune, forming because the drifting sand is stopped by the Tamarix bush and accumulates into a cone which becomes higher every year with the growth of Tamarix. It is a unique bio-geographical phenomenon formed by the collaboration between sandy-wind and Tamarix over a long period of time in desert environment. Related studies found that some of them have clear sedimentary vein structure composed of sand layer and Tamarix litter layer, and can be used in dating like tree rings. Also, the composition of them, eolian sand and Tamarix litter, contain a variety of environmental information and can be used to provide effective dating method and information carrier for high resolution environmental change research in this region.Based on the field investigation and survey, a Tamarix Cone which is 3.5m thick and has 168 clear sedimentary veins at the west shore of Lop Nur was chosen to study and collected 35 samples for pollen analysis in the interval of 5 layers. A higher resolution pollen record of aeolian deposit of the Tamarix Cone profile was obtained by laboratory procedures and the identification and statistics of the pollen. Based on the meteorological data of Ruoqiang weather station where is nearest from the sample site from 1956 to 2004 and the pollen data, the relationships between the dominant pollen types, the pollen assemblages and the climate factors through correlation analysis and detrended canonical correspondence analysis were discussed in order to reveal the climate factors which deeply affected the dominant pollen types and the pollen assemblages. The variation of annual mean temperature, mean July temperature and mean January relative humidity of the Lop Nur region during the past about 200a was reconstructed by using WA-PLS model. The characteristics of reconstructed temperatures and humidity were discussed in order to preliminarily reveal the environmental changes in the past 200a in the Lop Nur region, also compared with other results of the environmental change research, the extreme weather events, the change of water area and etc. in order to further study the evolution of paleoenvironment and paleoclimate, improve the research of environmental information in aeolian deposit of Tamarix Cone in the Lop Nur region using the pollen as environmental parameters, and provide theoretical basis and reference for understanding environmental changes over the past and predicting future environmental evolution better in the Lop Nur region. The main results are as follows:(1)The pollen assemblages in the Lop Nur region during the past about 200a were characterized by the herbaceous pollen whose percentage is up to 81.5% with Atemisia and Chenopodiaceae as the dominant pollen types; the second common group is the shrubby pollen with Tamarix as the dominant pollen types; the arboreal pollen is relatively spare and its percentage is below 13.4% ; the percentage of fern spores is only 0.2%.The plant types in the region during the past 200a had few changes.(2)The reconstructed and measured climate has less errors and they are very similar. Based on pollen assemblages and reconstructed climatic changes, the climatic change could be divided into three stages as follows: during the period of 1839 ~ 1886a A.D., the climate is relative cold-dry in the whole and has a trend changed from cold-dry to warm-humid; during the period of 1891 ~ 1941a A.D., the climate changed rapidly between cold-humid and cold-dry and warm-dry; during the period of 1946 ~ 2004 a A.D., the climate has changed from warm-dry to warm-humid.(3)Reconstructed temperature can well reflect the late Little Ice Age and the 20th century warming of global climate change, and reconstructed humidity has a better corresponding relation between the extreme weather events, the change of water area and etc.. Reconstructed climatic sequence can respond to the environmental evolution in Xinjiang and the same latitudes. The pollen concentration can reflect the information of human activities: since the late 19th century, the pollen concentration has been reduced continually with increasing of human activities.