Climate Change In Chongqing During The Holocene Reflected By Paleosol Profile In Fengjie County

The study about global change is becoming more and more important due to the conflicts between environmental issues and human activities. As one objective of the Past Global Change (PAGES) study, paleoclimate investigation can help us to understand controlling factors of climate change, and make possible prediction of future climate change. The Holocene is accompanied by the development and prosperity of the human society, which make this period becoming one of the most important phases of paleoclimate investigation. Chongqing locates in the mid-reach of Yangtze River, and on the east side of Tibet plateauthat which is the highest plateau in the world. The climate of this area is under the influence of East Asian Monoon, Indian Monsoon and Sibran High winter Monsoon, as well as the feedback of Yangtze River. The special geographical location makes the influencing factors of climate in Chongqing area become more complicated. Through conducting paleoclimate investigation in Chongqing area, we can detect the response of regional climate to Asia monsoon system under different conditions.The major objectives of this Master thesis are the stable isotopes and elemental geochemistry characteristics of the hydrological system and a paleosol profile in Fengjie County. Using the geochemical results from the paleosol profile, I reconstructe the paleoclimate conditions in the studying area during the Holocene. Our conclusions are summarized as follows:(1)The isotopic composition of the precipitation in the studying area shows the monsoonal rainfall feature: summer precipitation contributes the major part of the annual precipitation, whereas the winter amount contributes much less. Drip water in Xinya cave is from the precipitation, so that theδ¹⁸O of stalagmites is suitable for paleoclimate reconstruction and chiefly reflects the summer precipitation amount.(2)The contents of major and trace elements in the water samples reflect the geological background, different resources and the effect of the human activity depending on sample positions. One must pay great intention to the geological background when studying the major and trace elemental contents of water samples. (3)δ¹³C_org values of the paleosol profile denote that the woody plant(C3 plant) was the dominant vegetation in Chongqing area during the Holocene, reflecting humid climate.δ¹⁵N_org values reflect that the nitrogen source in the paleosol is natural.δ¹³N_org andδ¹⁵N_org values have the similar variational trends, demonstrating that the bulk organic matters are decomposed from plants. According to theδ¹³N_org andδ¹⁵N_org values, the climate was cold in early Holocene, but rapidly warmed up from early Holocene to middle Holocene. The climatic condition during the middle Holocene was warm. The summer monsoon became gradually weaker and the climate turned cold during the late Holocene. In the paleosol profile, the "suddenly warming, gradually chill" character of climate in the Holocene is also shown up. Due to high annual precipitation but mean annual temperature in the studying area during the Holocene, low "effective humidity" in net climatic condition may be resulted that may control the vegetation.(4)Based on the chemical characteristics, Fe and Mn in the paleosol profile were not leached out under the climate conditions. One may use variations in Fe and Mn contents in the paleosol profile in sub-tropical area as indexs for climatic changes.(5)Theδ¹³N_org values in the paleosol profile can reflect the climate change in Chongqing area during the Holocene, Which have a good comparison with the record of North Atlantic ice-raft debris on millennial-scale. The climate change in Chongqing area has been responsed to the global change drived by the solar radiation.