5 / 2021-09-09 16:58:42

Glacial meltwater produced high lake levels on the Tibetan Plateau during the late Quaternary period

Be-10, high lake levels, glaciations,, Tibetan Plateau,,glacial meltwater

High lake levels across the Tibetan Plateau (TP) have attracted much attention, but the mechanisms driving such lake level rises remain debatable. Dramatic lake expansions over the past decades are ascribed to the additional water supply from accelerated glacial melting, permafrost thawing, or precipitation increasing. Throughout the late Quaternary higher lake levels have been attributed primarily to enhanced monsoonal precipitation with glacial meltwater being a lesser contributor. We use absolute dating of the shorelines and glacial moraines, combined with modeled ice volumes, to examine the synchronicity of high lake levels and glaciations in the Nam Co’s catchment, and Linggo Co and Duoge Co North around the Puruogangri ice field within the endoreic basins of the TP. We find that lake water levels during Pleistocene are much higher than those during Holocene. The conspicuously exposed paleo-shoreline at 20-27 m above the current level of Nam Co in the southern TP formed during multiple short-lived periods - at similar water levels - that likely were initiated during MIS 6. This shoreline was subqequently resculpted in MIS 3. The second highest shoreline (14-18 m) was formed during the deglaciation associated with MIS 4 and reshaped during the last deglaciation. Four shorelines of Linggo Co in the innermost TP were formed during MIS 6 (22 m), MIS 4 (82-89 m), MIS 3 (94 m) and the LGM (66 m). The shoreline associated with MIS 6 was lower in altitude than late-formed shorelines associated with MIS 4, MIS 3 and the LGM. The MIS 3 shoreline was higher than the shorelines formed in MIS 4. The earlier shorelines are well-preserved; their ages are not affected by later higher water-level processes, suggesting that the high lake levels were short-lived. The periods during which these two clearly discernible shorelines of Nam Co and four shorelines of Linggo Co were at their widest extent appear consistent with the timings of the extensive glacial advances, suggesting that high lake levels were correlated with these glaciations. Any melting from the Puruogangri ice field could raise the water level of Linggo Co; glacial meltwater is the dominant source of water to this lake.  The reconstructed ice volume losses during LGM, MIS 3 and MIS 4 in the Nam Co’s catchment are equivalent to a rise of 66-75 m in the Nam Co’s water levels. The climates conditions during MIS 6, MIS 4, MIS 3, the LGM, and the last deglaciation were generally colder and drier, but the lake levels during these periods were higher than those of the Holocene, suggesting that the increasing precipitation was not a major factor for these high lake levels. High lake levels also appear synchronous with Quaternary glaciations across the semi-arid areas on the TP and its surrounding mountains. Paleoglaciers would have contributed substantial meltwater to maintain high lake levels during late Quaternary on the TP.