Regional characteristics and mechanisms of lake water level decline in the Tibetan Plateau since 2 000 years ago

The Tibetan Plateau (TP) was divided into three zones based on the influence of the Asian summer monsoon and the westerlies. By comparing multiple proxy indicators in sediments with late Holocene volcanic activity, the Northern Hemisphere temperatures, and the Asian monsoon index, the reasons for the decline in plateau lake levels ～2 kaBP were explored and the spatial differences in lake responses to climate fluctuations in the different zones were analyzed. Results show that the decline in lake water level in the southwestern part of the TP is greater than in the northwestern part, and even greater in the northeastern TP. This may be due to the weakening in the intensity of the Indian Summer Monsoon (ISM), which made lakes in the southwestern TP more dependent on the ISM precipitation replenishment and thus more sensitive to the reduction in water vapor flux brought by the ISM. Moreover, during this period, the phase of the North Atlantic Oscillation (NAO) shifted from negative to positive, leading to the increase in water vapor convergence in the northern part of the TP with more precipitation there, while the southern part of the TP received less rainfall, resulting in a generally greater decline in water levels in the southern lakes compared to those in the north. The main cause of the climate turning to colder and drier in the TP ～2 kaBP is attributed to the intensification of El Niño. In addition, the different phases of the Southern Annular Mode in winter and summer through complex ocean-atmosphere coupling processes crossing the equator, also played a role in cooling and dehumidifying the climate of the TP.