Late Holocene Climate Change And Its Influences On Ancient Civilization In Horqin Sandy Land

Under the background of global warming, the trends and regularities of climate change is one of the focuses of society and academic circles. Holocene is the key period of the development of human society, and Holocene climate change is one of the main bases to predict the future evolution of our living environment. The Horqin sandy land in the western part of northeast China is located in the present margin of East Asian Monsoon zone, and its landscape is sensitive to the climate change. This paper present a high-resolution climate evolution record during4300～1000cal a BP derived from sequential aeolian sediments of Liuhutun section in the northeastern frontier of the Horqin sandy land. The2.96-m sandy paleosol/sandy loess/fine sand section, with a chronological support of7radiocarbon dates, has been analyzed for grain size distribution, CaCO3content, organic matter content and environmental magnetic parameters. With support from high-resolution climate record, by comparing with ancient civilization development in the Western Liaohe River Basin and dynastic transitions in the middle and lower reaches of the Yellow River, the relationship between climate change and cultural development was discussed in detail.The results show that4300～3800cal a BP was the warmest and wettest epoch during the study period, with a trend of becoming cooler and drier. The Holocene Optimum in this region is supposed to end at3800cal a BP. Climate between3800and1700cal a BP was cold and dry, this period can be subdivided into two phases with3000cal a BP as a boundary. Climate became cooler and drier before3000cal a BP, afterwards the winter monsoon stayed at a strong level while the summer monsoon gradually strengthened.1700～1000cal a BP was a warm and humid period, but the climatic conditions were inferior to the Holocene Optimum. On the millennial scale, our records show an anti-correlation between the strength of summer and winter monsoon. The main trends of climate changes during this period can be compared with stalagmite δ18O records of the strength of summer monsoon in the south China. Late Holocene climate change in this region was mainly driven by solar radiation, on the one hand the long-term trend of climate change was controlled by solar radiation change in orbital scale, on the other hand the centennial scale cyclical fluctuation of the climate was driven by the solar cycle.Climate change is an important trigger of the ancient civilization transitions and dynastic changes. Precipitation and temperature play an important role in the cultural collapses in the Western Liaohe River Basin. Specifically, the collapses of Xiaoheyan, Lower Xiajiadian and Upper Xiajiadian culture, nomadic southward invasion during the Northern and Southern Dynasties, and the decline of Tang Dynasty, are related to the environmental degradation caused by precipitation and temperature decrease. Cultural prosperity in the early Tang Dynasty is inextricably linked with the suitable climatic conditions. Different modes of production have different requirements on the climatic conditions, thus, human adapt to environmental changes through the transformation of the production methods. In prehistoric civilizations, climate change had an important influence on the choice of the mode of production; in historical period, impact of political and cultural factors on the human society increased significantly. With the development of the society, human’s ability to adapt to climate change had enhanced obviously.Furthermore, detailed environmental magnetism researches show that there are only a few magnetic minerals in the aeolion sediments of Liuhutun section, contents mainly magnetite with few haematite, and perhaps maghaemite and/or goethite. The main magnetic grain sizes are in stable single domain (SSD) and superparamagnetic (SP) size fractions. Those fine-grained magnetic particals can’t be completely formed by pedogenesis, lithogenic magnetic minerals of source materials might be already in SSD size fractions. The relationship between magnetic susceptibility and environmental factors is complicated, while XARM/Xlf and XARM/SIRM, which denote magnetic grain size, can be used as paleoclimatic proxies. Because the aeolian magnetic particals are in SSD size fractions, XARM/Xlf and XARM/SIRM show an inverse correlation with pedogenesis, which are different from pedogenic mechanism of loess-paleosol sequences in the Chinese Loess Plateau.