The Pollen Analysis And Climate Changes In Holocene Of Xiaogou Section In Huining, Gansu

This paper has used the Charcoal in stratum which adopted AMS¹⁴C to establish the more accurate sequences of the age of Xiaogou section in Huining, west of Loess Plateau. According to pollen analysis, this thesis has resumed the change of middle-late Holocene vegetation and climate in Huining. On the basis of this, the change sequence of the middle-late Holocene environment is furtherly investigated together with the data of other places, especially the relatively reliable historical data, revealing the course that the climate gradually changed from wet to dry in middle-late Holocene in the west of Loess Plateau. The result of the research indicates that (1) from 7000 to 28a B.P., the vegetation of Xiaogou section in Huining went through a serious of change, the course like that: Needleleaf and Broadleaf Mixed Forests—Forest-steppes—Needleleaf and Broadleaf Mixed Forests—Forest-steppes—Deserts-steppes; (2) The climate in Huining was relatively wet and warm in the middle-late Holocene (7～3.7ka B.P.); (3) Most of the time in this region, the climate was quite cold or cold-dry expect 7000a B.P.～6460a B.P. and 5800a B.P.～4670a B.P.; (4) During 7000a B.P.～6460a B.P. and 5800a B.P.～4670a B.P., the vegetation was in bloom, and the climate was relatively wetness, maybe which was the optimum period; (5) There were some short climate changed suddenly in the middle Holocene, it was showed that the climate was also instability. The paper attempts to contrast the pollen data with the cuve of 2000y' average year temperatures, together with the Huining country annals, to resume the relatively complete climate change course of about 2000y in Huining. It is indicated that Huining entered the small ice age around 2000y ago, when the warm-cold climate change was relatively large, which lasted to the end of Southern and Northern Dynasties. A comparison suggests that the climate probably tended to become cold and dry from Sui dynasty to Tang dynasty, and that the climate might be warm and dry from 700a A.D to 1000a A.D. In Song dynasty, the climate, however, was warm and wet, and the vegetation was in bloom. In Yuan dynasty the climate change turned to be stable, still being wet and warm. However, the pollen density decreased greatly since Ming dynasty, and accordingly, the temperature descended, indicating that the climate of this period belonged to the typical cold-dry kind. That is consistent with the result of Si Yafeng, in which he studied theδ¹⁸O in Guliya ice, and concluded that the climate was dry and lower-warm in 960～280a A.D., dry and mid-warm in 1500～970a A.D., and the period from 1920 to 1510a A.D. was the small ice age when warm-cold change was fierce. It is still in the exploration stage to draw on pollen data to resume such a short scale climate change, so further research should be made to show whether the result is reliable or not.