Late Holocene hydroclimatic variations and possible forcing mechanisms over the eastern Central Asia.

Hydroclimatic variations over the eastern Central Asia are highly sensitive to changes in hemispheric-scale atmospheric circulation systems. To fully understand the long-term variability and relationship between hydroclimate and atmospheric circulation system, we present a high-resolution lascustrine record of late Holocene hydroclimate from Lake Sayram, Central Tianshan Mountains, China, based on the total organic carbon, total nitrogen, and carbonate contents, carbon/nitrogen ratios, and grain size. Our results reveal four periods of substantially increased precipitation at the interval of 4000–3780, 3590–3210, 2800–2160, and 890–280 cal yr BP, and one period of slightly increased precipitation from 1700–1370 cal yr BP. These wetter periods broadly coincide with those identified in other records from the mid-latitude Westerlies-dominated eastern Central Asia, including the northern Tibetan Plateau. As such, a similar hydroclimatic pattern existed over this entire region during the late Holocene. Based on a close similarity of our record with reconstruction of North Atlantic Oscillation indices and solar irradiance, we propose that decreased solar irradiance and southern migration of the entire circum-North Atlantic circulation system, particularly the main pathway of the mid-latitude Westerlies, significantly influenced hydroclimate in eastern Central Asia during the late Holocene. Finally, the inferred precipitation at Lake Sayram has increased markedly over the past 100 years, although this potential future changes in hydroclimate in Central Asia need for further investigation. [ABSTRACT FROM AUTHOR]