Hydroclimatic dynamics over the western Tibetan Plateau since the Last Glacial Maximum: A critical review

The Tibetan Plateau (TP), often referred to as the Asian water tower, is affected mainly by interactions between mid-latitude westerlies (MLW) and the Asian summer monsoon (ASM) and has been linked to continental-scale climate dynamics and human evolution. Despite numerous high-resolution studies of Holocene climatic change, the hydroclimatic evolution of the western Tibetan Plateau (WTP) since the Last Glacial Maximum (LGM) remains insufficiently resolved. Here we compiled extensive multi-proxy evidence from lake sediment, peat, speleothem, loess, ice core, and glacial moraine archives, and reinterpreted them within an explicit lake water-balance framework that distinguishes precipitation, effective moisture, and lake level. Our results revealed that an apparent LGM dry-wet contradiction was primarily caused by proxy sensitivity, in which ecological proxies, which mainly record the summer or growing-season conditions, showed drought conditions whereas physical and chemical proxies, which integrate the basin water balance, inferred high lake level and precipitation. However, the latter appears to be more sensitive to the enhancement and southward migration of the MLW and a weakened Indian summer monsoon (ISM) under the extremely cold LGM conditions. Although most simulations indicated reduced LGM evaporation and precipitation, the high-resolution transient simulations have shown that the high lake levels can be sustained by reduced evaporation and glacial meltwater. After the Heinrich Stadial 1 event, a generally wetter trend and persistently high lake levels were possibly caused by glacial meltwater and a strengthened ISM, which was interrupted by the Younger Dryas. During the early–middle Holocene, the strengthened ISM penetrated into the northernmost WTP and probably affected the Pamir Plateau, whereas declining Northern Hemisphere summer insolation led to the weakened ISM but enhanced MLW during the late Holocene, shaping regional hydroclimate. This review clarifies the climatic dynamics of the MLW and ISM over the WTP since the LGM, and indicates that the high-resolution and well-dated proxy records and model simulations are further required to resolve the complexities of MLW–ISM interactions.