Asian summer monsoon variability during the late glacial and Holocene inferred from the stable carbon isotope record of black carbon in the sediments of Muge Co, southeastern Tibetan Plateau, China

A sediment core from an alpine lake (Muge Co) from the southeastern margin of the Tibetan Plateau was analyzed for sediment grain size distribution and the carbon isotopic composition of black carbon in order to reconstruct Asian summer monsoon variability over the last 12 ka. Five major climatic stages were identified: (1) From 12 to 10.5 cal. ka BP, a cold and dry climate prevailed, corresponding to the Younger Dryas in the North Atlantic; (2) from 10.5 to 9.2 cal. ka BP, precipitation increased rapidly but was interrupted by a pronounced cold and dry phase at about 10 cal. ka BP; (3) from 9.2 to 6.2 cal. ka BP, the Holocene climatic optimum was reached and maintained; (4) from 6.2 to 2.5 cal. ka BP, the climate gradually became cooler and drier; (5) from 2.5 cal. ka BP to the present, a climatic reversal toward wetter conditions occurred. The trend of our reconstructed Asian summer monsoon precipitation record is similar on orbital and millennium timescales to that of other records from the Asian monsoon region. Although the maximum monsoon intensity recorded in the Muge Co sediments lagged the peak of Northern Hemisphere insolation by ~3.0 ka, the strengthening trend was in phase with the rise in the Western Pacific Warm Pool sea surface temperature. Therefore, we suggest that the tropical ocean temperatures may have been the major driver of Asian summer monsoon precipitation in the southeastern Tibetan Plateau. In addition, other factors such as sea-level rise and temperature in the North Atlantic region may have played an important role in the evolution of the Asian summer monsoon since the last deglaciation. However, human activity may have affected the monsoon proxies during the last 2.5 ka, and further studies are needed to distinguish the effects of climate and human disturbance.