Drivers of late Quaternary lake level fluctuations of Khyargas Nuur, western Mongolia - glacial meltwater discharge or atmospheric moisture supply?

This study presents the first comprehensive late Quaternary chronology of lake level variations of the Khyargas Nuur (western Mongolia), based on a geomorphological approach supported by luminescence dating of relict shorelines and lacustrine sediments. The endorheic Khyargas Nuur in the Basin of Great Lakes is the ultimate sink of a sequential water and sediment cascade from the adjacent Mongolian Altai and Khangai Mountains. Several intercalated lakes repeatedly joined as one major paleolake, as evidenced by various morphological shoreline features. Situated in the mid-latitude Westerlies-dominated climate regime of Arid Central Asia and affected by the distant effects of the East Asian Summer Monsoon, the dynamic climate of the Basin of Great Lakes is determined by the co-evolution of these atmospheric circulation systems. Our observations comprise 11 distinct paleolake levels between +7 m and +188 m above modern lake level (aml). Calculations of paleolake extent and water volume emphasize the periodically enhanced inflow and gradual capture and abandonment of upstream-located lakes. In the regional to global paleoclimatic context, our results reveal three distinct phases of lake level dynamics: (i) A transgression to a maximum level of +129 m aml during Marine Isotope Stage 5c (104.7 ± 14.4–88.8 ± 12.7 ka) primarily controlled by increased atmospheric moisture supply from the Westerlies. (ii) A post-Last Glacial Maximum lake expansion to a level of +118 m aml around 14 ka, ultimately controlled by enhanced glacial meltwater discharge into the basin. This is followed by a lake regression throughout the late Glacial to early Holocene transition in response to a gradually decreasing meltwater supply and a drier climate. (iii) A late Holocene transgression to +15 m aml reflecting a general Holocene wetting trend across arid Central Asia, followed by small-scale level fluctuations post 2.6 ka.