Abstract:

A relatively high resolution pollen record and data of loss of ignition (LOI), grain size and susceptibility of the Daxigou profile in the head area of the Urumqi River, central Tianshan Mountains, revealed new information about vegetation changes and environmental evolution since 3.6 ka BP. Results showed that from 3.6 ka BP to present, climate was unstable with multi-changes of warming-cooling and wetting-drying. From ca. 3.6 to 3.2 ka BP, climate was warmer and more humid than today. Climate changed to cooler and drier between ca. 3.2 and 2.0 ka BP, coinciding with a glacier advance in the head area of the Urumqi River. From ca. 2.0 to 1.4 ka BP, climate became warmer and more humid again. From ca. 1.4 to 0.5 ka BP temperature and humidity went on increasing and a period of Climatic Optimum since 3.6 ka BP might occur. A few limnetic hydrophytes pollen are counted for all zones, indicating a freshwater habitat since 3.6 ka BP in this region. Based on synthetically analysis of ecological characteristics and dispersal of spruce pollen, the abundance of Picea is influenced by treeline moving upward, valley wind and glacier ablation. Statistics of charcoal concentration and susceptibility further suggest that fires may have occurred in this region since 0.5 ka BP and the peak value of charcoal might be related to human activities.

Key words: Tianshan Mountains, vegetation changes, climatic change, pollen record, charcoal, multiproxy data