Shrinking lakes in Tibet linked to the weakening Asian monsoon in the past 8.2 ka

Abstract

Expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation, linked closely to changes in strength or position of atmospheric circulation. In Tibet, there are many such lakes with paleo-shorelines that can be used for reconstructions of climate history. Despite the fact that many paleo-shorelines are well preserved in Tibet, dating them has been seriously hindered by various difficulties. Here we present the first optical dating chronology for a series of paleo-shorelines in Zhari Namco, the third-largest inland lake in central Tibet. Our results indicate that the lake level has dropped 128m over the past 8.2ka. Younger shorelines are found at lower altitudes, indicating that the shorelines follow a geomorphic-chronological order and a broadly continuous trend of stepwise shrinkage. The surface area of Zhari Namco has shrunk in size from 4605km2 at 8.2ka ago to 996km2 at present; 300km3 of water has been lost from this lake. Such a loss in water implies a significant reduction in precipitation over the past 8.2ka, a likely result of a weakening Asian monsoon. Following the decreasing precipitation since the early Holocene, this area has become increasingly arid.