Late deglacial and Holocene vegetation and climate change at Lake Mapam Yumco, southwestern Tibetan Plateau

Environmental changes on the Tibetan Plateau (TP) and their responses to the Indian summer monsoon (ISM) and the westerlies have attracted significant attention. However, our understanding of regional vegetation and climate changes influenced by the ISM from the Arabian Sea and the westerlies in the southwestern TP remains limited. Here, we present a pollen record from Lake Mapam Yumco covering the late deglacial to the Holocene. Results show that alpine meadow was sparsely distributed around the lake, with relatively high moisture from 13.5 to 11.7 cal ka BP. The early Holocene (11.7–8.3 cal ka BP) was the most humid period, marked by persistent alpine meadow and expanding steppe. During 8.3–4.2 cal ka BP, the climate became drier, with alpine meadow steppe dominating. After 4.2 cal ka BP, vegetation shifted to sparse dry steppe. Moisture conditions at Lake Mapam Yumco were humid in the late deglacial and early Holocene but drier in the late Holocene compared to the eastern TP, due to the ISM from different pathways and the influence of the southern branch of the westerlies. The stepwise drying trend in the Holocene reflects that the regional climate was mainly controlled by the ISM, which was driven by the summer insolation at 30°N and the position of the Intertropical Convergence Zone. Exotic pollen studies underscore the crucial role of the westerlies and El Niño-Southern Oscillations in atmospheric circulation. Dry events in the Holocene highlight that the North Atlantic region also impacts the climate in the southwestern TP.