Hydroclimate variability in southeastern Tibetan Plateau since the late Quaternary: Insights from hydrogen isotopes in sedimentary leaf waxes

Hydroclimate variations in the Tibetan Plateau, particularly its southeastern region, significantly influence downstream agricultural and ecological systems. However, the dynamics of these changes remain inadequately understood. In this study, we present a 28.6 thousand-year record of precipitation hydrogen isotopes (SDp) derived from sedimentary leaf wax n-alkanoic acids (C30, SDwax) from Mang Co Lake, a lake in the southeastern Tibetan Plateau. Our analysis interprets SDp as a proxy for Indian Summer Monsoon (ISM) intensity, revealing its strongest phase during both the early Holocene and 28.6-26.5 calibrated thousand years before present (Cal ka BP), as well as its weakest during the Last Glacial Maximum (LGM). We find that summer insolation is the primary driver of ISM variability on the orbital scale over the past 28.6 ka. Millennial scale SDp variability reflects interactions between the summer monsoon and the westerly jet (WJ). The SDp record reveals that in the periods of 5-3 Cal ka BP and 1-0 Cal ka BP, a weakened ISM coincided with the WJ's prolonged residence south of the Tibetan Plateau. Abrupt cooling events due to albedo feedback of ice and snow in high latitudes are inferred to have played a critical role in modulating the atmospheric circulation patterns, including the position and intensity of the WJ and ISM. Our findings emphasize the high sensitivity of the southeastern Tibetan Plateau's hydroclimate to global climate changes, necessitating future reconstructions with improved temporal and spatial resolution.