EVIDENCE FOR A WARM AND HUMID CLIMATE PERIOD AND ENVIRONMENTAL CHARACTERISTICS IN THE ARID ZONES OF NORTHWEST CHINA DURING 2.2-1.8 KABP

Ice cores, tree rings, river and lake sediments, lake terraces, historical documents and palaeosols document aspects of climate changes in northwestern China during the Western and Eastern Han Dynasties (206 BC ¨C 220 AD). A reconstruction of decadal means of annual mean temperature and precipitation fluctuations were derived from variations of d18O and net accumulation rates in the Guliya ice core. The results show that during the period of interest vast areas of northwestern China experienced a period of higher temperatures and higher precipitation than today, lasting until the 5th century AD. These conditions resulted in a marked increase in discharge of several big endorheic river systems, such as the Tarim River, the Keriya River and the Manas River. As a consequence, water levels in appendant terminal lakes rose, e. g. at Lop Nur, Manas Lake and Baijian Hu. Lake surface areas expanded and lake desalting occurred also at lakes in intermontane basins such as Balikun Hu and Qinghai Lake. These warm and moist conditions during the Western and Eastern Han Dynasties might have been responsible for large-scale agricultural production activities and a local socioeconomic boom that is documented by the occurrence of the famous ruin groups of Loulan, Niya and Keriya. The following desiccation phase led to a deterioration of water resources, and most oases tended to fade and finally were abandoned. The appearance, development, flourishing and final abandonment of each great ruin group is closely associated with regional climate change at that time.