Asian Summer Monsoon changes the pollen flow on the Tibetan Plateau

Abundant evidence has revealed that the Tibetan Plateau's uplift influenced the evolution of the Asian Summer Monsoon system. Pollen, as fine powdery substance, which can be easily transmitted by wind currents, has great potential to be used as an indicator of the monsoon's intensity and flow direction, and used for the detection and evaluation of the ancient monsoon on the Tibetan Plateau. Hence, it is extremely important (and necessary) to achieve a better understanding of the modern pollen deposition model on the plateau. However, most of the previous studies mainly focused on the coupling of surface pollen deposition and regional vegetation and the establishment of the transfer function between pollen-vegetation-climate on the Tibetan Plateau, but largely neglected the direct correlation of the modern surface pollen deposition and the monsoon's intensity and its current direction. We have comprehensively analysed a dataset of the surface pollen on the Tibetan Plateau and discovered that 1) the surface pollen assemblage can reflect the alpine meadows, steppe and desert vegetation which means that surface pollen data can be used to assess the deep-time vegetation. 2) most of the exotic pollen are from trees, the spatial distribution trend of these tree pollen's relative abundance is highly coupled with the path of the Asian Summer Monsoon and the extent to which it encroached on the Tibetan Plateau. These results unambiguously demonstrate that tree pollen deposition on the Tibetan Plateau is dominated by the Asian Summer Monsoon, i.e., the upslope movement of the modern Asian Summer Monsoon drives the spread of pollen rain from low-altitude vegetation to high-altitude areas. If a similar scenario happened at different stages of the Asian Summer Monsoon evolution and the Tibetan Plateau uplift, the pollen buried in the sediments have the potential to reflect the current direction and intensity of the Asian Summer Monsoon at that time. Moreover, it would provide a simple and potentially practical proxy for the study of the evolutionary history of the Asian Summer Monsoon, e.g. wind direction and intensity, under the influence of the plateau's uplift.