Spatiotemporal patterns of pollen-based Holocene precipitation variations in the Altai Mountains and the surrounding areas

The existing depictions of Holocene moisture variations in the Altai Mountains and the surrounding areas (i.e., the examined area) remain controversial. This study quantitatively reconstructed 16 mean annual precipitation (Pann) sequences from available fossil pollen datasets (3 sequences of our own and 13 sequences from external datasets) and combined them with 13 already available Pann sequences to depict the spatiotemporal patterns of the Holocene precipitation variations in the examined area. This resulting analysis reveals a general upward trend in Pann during the Holocene in the southern Altai Mountains and the immediate upper-wind region (e.g., southern Siberian Plain and eastern Kazakhstan Hills). This rising trend might be causally linked to the concurrent rising trend in the sea surface temperature (SST) in the North Atlantic Ocean and the long-term weakening trend of the cool airmass over southwestern Siberia. In contrast, the eastern Russian Altai and Sayan Mountains, situated on the leeside of the Altai Mountains, experienced a consistent decline in Pann since ∼9000 cal. yr BP. And, this decline was probably a combined result of the temperature anomalies in the middle-high latitudes of Northern Hemisphere and the SST in the Western Tropical Pacific Ocean. The Holocene Pann in the lowlands to the south of the Altai Mountains displayed a rise from ∼10,500 to ∼6000 cal. yr BP, a U-shaped trough from ∼6000 to ∼3500 cal. yr BP, and a slight decline afterward. This pattern was most likely associated with the SST in the North Atlantic Ocean before ∼5000 cal. yr BP and with the SST in the Western Tropical Pacific Ocean after ∼5000 cal. yr BP.