Climate instability during the last deglaciation in central Asia, reconstructed by pollen data from Yili Valley, NW China

Abstract

An extended pollen record with grain size analysis and AMS 14C dating is provided for a palaeolake section which is located in an intermountain basin in Yili Valley, Xinjiang, NW China. Covering the late MIS 3, early MIS 2 and the last deglaciation, vegetation variations and climate events are discussed in relation to changes in pollen assemblages and Artemisia/Chenopodiaceae (A/C) ratios. The presence of montane forest-steppe dominated by Picea and Taraxacum indicates a relative humid climate in the study area during late MIS 3 (before 31.5calkyrBP). Picea forest disappeared and the vegetation dominated by Chenopodiaceae shows the climate became dry from 31.5 to 14.7calkyrBP. The sediments of Last Glacial Maximum (LGM) period are absent in the section probably. Betula-Picea mixed forest occurred at 14.7calkyrBP and corresponds to the onset of the warm Bølling period in the North Atlantic. A long dry period was detected from 14.5 to 13.6calkyrBP on the basis of the occurrence of Chenopodiaceae desert. A subalpine meadow community dominated by Geranium covered the area during 13.6–13.4calkyrBP, suggesting lower temperatures at this time. This may coincide with the Older Dryas (OD). The most humid period in the record occurred between 13.4 and 12.9calkyrBP, which coincides with the warm Allerød period. Dry conditions prevailed from ~12.9 to 11.7calkyrBP in the area, coinciding with the Younger Dryas (YD) in the North Atlantic. Within this period a three-phase climate fluctuation was detected, which can be summarized as follows: a dry early YD (12.9–12.6calkyrBP), a slightly moister mid-YD (12.6–12.0calkyrBP) and a very dry late YD (12.0–11.7calkyrBP). These millennial to century-scale climatic events in Yili Valley correlate well with other palaeoclimate records in North Hemisphere, suggesting that these events probably originate from same mechanisms.