Quantitative precipitation reconstruction since mid-Holocene from northeastern Tibetan Plateau: Implications for interplay between Asian summer monsoon and Westerlies

Both the Asian Summer Monsoon (ASM) and Westerlies exhibit strong impacts on climate changes of the Tibetan Plateau (TP), but little is known about their contributions to regional precipitation during the Holocene. Here we reported a pollen record from Lake Alake, based on which the quantitative mean annual precipitation (PANN) was reconstructed. Herbaceous taxa of Cyperaceae, Poaceae, Chenopodiaceae, and Artemisia were dominant in Alake pollen assemblage whose variations were mainly affected by humidity changes. The precipitation was high in 7200–5400 cal. yr BP, followed by decreasing trends in 5000–3000 cal. yr BP, and obviously increased after 3000 cal. yr BP. The variations of PANN in the Alake record suggest that high precipitation in middle Holocene was primarily contributed by the ASM driven by orbital forcing of insolation. However, the rising trend of PANN during the late Holocene probably indicated the increased of non-monsoonal precipitation and highlighted the contribution from the Westerlies. Our results suggest that the variation of precipitation transported by Westerlies might have reduced the seasonal variability of precipitation and contributed to the long-term wetting trend on the northeastern TP during the late Holocene.