Westerlies and Monsoon Climate Systems Shape Holocene Moisture Patterns in the Southern Tibetan Plateau: Evidence from Aeolian Sedimentary Records

The southern Tibetan Plateau (TP) is a crucial component of the “Asian Water Tower,” whose moisture dynamics influence both the terrestrial ecosystems and welfare of a large human population across Asia. However, the pattern of its moisture evolution and interactions with atmospheric circulation remain unclear, limiting our understanding of the current and future hydroclimatic changes. Here, we present geochemical, environmental magnetic, and color proxy records derived from a well-dated, high-resolution aeolian sedimentary record. Based on detailed evaluation of the environmental proxies and integrating data from other aeolian records, we investigated the spatial heterogeneity of moisture modes and their atmospheric responses. Our findings reveal two distinct Holocene moisture evolutionary modes in the southern TP, with their boundary delineated by the Shannan wide-valley, which roughly coincides with the southernmost northern boundary of the modern monsoon. In the western region, moisture was co-influenced by the mid-latitude Westerlies (MLW) and the Indian summer monsoon (ISM), characterized by higher moisture during the early Holocene due to strong ISM precipitation. This was followed by a sharp decrease in moisture and then a gradual increase from the middle Holocene onward, under the influence of an enhanced winter MLW. In contrast, the moisture mode in the eastern region was predominantly influenced by the ISM and shows a general decreasing trend. Using climate simulations, we project a future scenario where, as the winter MLW weakens and the ISM strengthens, moisture in the southern TP will experience a decreasing trend in the west and an increasing trend in the east.