Mid-Holocene Climate Change In JingNing, GanSu Province

The western part of the Chinese Loess Plateau has experienced a series of environmental changes during the mid-Holocene. The reconstruction of the climatic history of the Chinese Loess Plateau is important for understanding and predicting present and future environment and climate changes in the north-western part of China. In this thesis, the author reconstructed the temperature and precipitation trends during 8.5-2.7kaBP, based on JingNing loess profile (N35°35′00″, E105°59′30″), which is located in the western Loess Plateau. On the basis of outdoor observation and indoor experimental analysis, I select three proxy substitute indexes: grain-size, magnetic susceptibility and CaCO₃. Through the integrative analysis of these climatic substitute indexes, the thesis reveals the process of the climate changes during mid-Holocene.This thesis draws the following conclusions:(1) During 8.5-7.6kaBP, the summer monsoon was stronger and the winter monsoon weaker, the temperature and the precipitation both raised. The climate was warm and wet.(2) During 7.6-6kaBP, the climate changes little, the summer monsoon was still strong and the winter monsoon was weak. The pedological process was becoming strong. The temperature was high. Although part of climatic substitute indexes revealed some aridity trends in this district, the climate of this period was still characterized by warm and wet.(3) During 6-5kaBP, the climate deteriorated. The summer monsoon became weaker and the winter monsoon started to become stronger. Moreover, the climate fluctuated towards cold and arid once during this period. The precipitation decreased and so did the temperature. So the climate of this period was characterized by cold and arid.(4) During 5-3.9kaBP, the climate turned warm and wet again. The summer monsoon turned strong and the winter monsoon became weak, the pedological process was stronger and the grain-size became finer.(5) During 3.9-2.7kaBP, the grain-size became coarser and the summer monsoon weakened. The temperature decreased, and the climate turned cold. However, the CaCO₃ substitute index revealed the increasing of the precipitation, this may because the precipitation changes slower than the temperature. In general, the climate was cold in temperature, arid or wet in precipitation.(6) There was a climatic fluctuation towards cold and arid in 5kaBP. The winter monsoon became strong and the grain-size became coarser, meanwhile, both the temperature and precipitation decreased. The climate became cold and arid. This climate deterioration was also be found somewhere else in China and in the world. So this phenomenon, in the other hand, proved that the climate change in JingNing district was global and prevalent.