Climatic Change Of Xi'an Area During The Last About 10 000a

Holocene is the period from the end of the last Glaciation to present. During this period human society rapid develope and many human civilizations have been created.So the study of climatic change during this period become the focus of APGES. Xi'an area lying in the south edge of Loess Plateau has the very thick loess deposits, in particular the loess and paleosol formed by wind blown since about 10,000a.B.P. to now. Ancient human had lived in Xi'an area in Neolithic Age and Xi'an is also the capital of 13 Dynasties of Ancient China ,so the study of mutual impaction between human and climate of Xi'an area is very typical. We selected two holocene loess and paleosol profiles in village of Yubaotou of Shenheyuan and village of Xinzhuang of Jingyang of Xi'an area.then we took high-resolution samples in those profiles,which were analysised in the laboratory through the mothed of magnetic susceptibility, particle size and AMS¹⁴C dating. We made analysis on climatic change in Xi'an area of the Loess Plateau since about10,000a.B.P. to now based on laboratory test data. This research provided data for forecasting the future evolution of the climate in Xi'an area ,and provided a new example for the research of holocene climate of the whole Loess Plateau region and the research on ancient climate of global even.Through this research, we reached the following conclusions on climatic change of Xi'an area since about 10,000a.B.P. to now:(一)The early Holocene(10000～8500a.B.P.), climate gradually became warming from cold in the late Pleistocene, precipitation increased, a soil strength increased. the summer monsoon took an advantage gradually replacing of the winter monsoon.(二) The mid-Holocene (8500～about 3100a.B.P.), climate was warm and humid, precipitation significantly increased, soil viscosity and leaching was very strong, the summer monsoon had occupied the absolute superiority over the winter monsoon .This period included four stages(:1)From 8500a.B.P. to 6500a.B.P. the climate had a cooling trend though the whole climate was warm and humid. In about 6800a.B.P. temperature reached the lowest point of the stage. there may be an extreme weather event. After that climate was rapid warming.(2)From 6500a.B.P. to 5500a.B.P. climate became cold obviously. And get the coldest of this stage in about 5800a.B.P., the whole process last about 700 a. then climate started a rapid warming lasting About 300a .(3)From 5500a.B.P to 4500a.B.P. climate in the relatively small range was instable.There was a small cooling trend in general, meeting the minimum temperature in about 4500a.B.P..And then temperature increased slowly and fluctuantly lasting about 500a.(4)From 4000a.B.P. to about3100a.B.P. this climate fluctuated fiercely. The overall trend was cooling down, meeting the minimum temperature in about 3100 a.B.P..(三)The late Holocene (3100⁰a.B.P.), the monsoon transformed in this stage. Weather became cool and drought, and the layer of loess Late Holocene L0 and farming-Ms was formed. This stage included two stages:(1) From 3100a.B.P. to 1900a.B.P. climate was slowly warming.(2)From1900 a.B.P. to now climate had a warming trend and farming-Ms was formed.