Climatic variations over the last 4000 cal yr BP in the western margin of the Tarim Basin, Xinjiang, reconstructed from pollen data

Abstract

The nature of Holocene climate patterns and mechanisms in central Asia are open areas of inquiry. In this study, regional vegetation and climate dynamics over the last ca. 4000years are reconstructed using a high resolution pollen record from the Kashgar oasis, on the western margin of the Tarim Basin, central Asia. Ephedra, Chenopodiaceae and Cannabaceae dominate the pollen assemblages, and Chenopodiaceae/Ephedra ratios and percentages of long-distance transported pollen taxa are used to infer regional variations in moisture and vegetation density. Three periods of increased humidity are identified, from ca. 4000–2620calyr BP, ca. 1750–1260calyr BP and ca. 550–390calyr BP and these periods coincide with the respective Holocene Bond Events 2, 1 and 0, which are reported in the North Atlantic. Any increase in strength, or southward migration, of the mid-latitude westerlies would result in more precipitation and meltwater on mountains surrounding the study site. Warm and dry conditions are detected between ca.1260 and 840calyr BP (AD 690–1110), and cool and wet conditions are detected between ca. 840 and 680calyr BP (AD 1110–1270), during the Medieval Warm Period (ca. AD 800–1200). The climate variations in the Kashgar region over the last 4000years appear to have been dominated by changes to the westerly circulation system and glacier dynamics on surrounding mountains. However, the question of whether the Asian monsoon delivers precipitation to the western Tarim Basin, a region that is influenced by several climate systems, is still open to debate.