Mega-lakes in the northwestern Tibetan Plateau formed by melting glaciers during the last deglacial

Rapid lake expansions along with intensive glacier loss in the Tibetan Plateau (TP) in recent decades indicate an enhanced hydrological circulation. Well-preserved paleo-shorelines up to ∼200 m above modern levels in the TP attest to much greater lake expansions in the past and serve as analogues for future lake evolution under climate changes. Mega-lakes in the inner TP, defined by the highest paleo-shorelines, were mainly formed in the early–middle Holocene and are mainly attributed to a high monsoonal rainfall. However, the effect of melting glaciers on the mega-lakes was rarely evaluated, and reliable mega-lake ages are scarce, especially in the northwestern TP (NWTP). We studied six mega-lakes in the NWTP by dating the highest paleo-shorelines using optical dating of multiple and single grains and then reconstructing the paleo-hydrology. The results show that four mega-lakes existed during the last deglacial (16.3–12.6 ka). They had lake levels 53–269 m higher than today and areas up to 7.3 times larger than the modern lakes, containing up to 105.4 km3 more water. A comparison of mega-lakes across the TP and correlation with independent paleoclimatic records reveal that these mega-lakes attained larger relative sizes (lake area/basin land area ratio) under a dry climate and intensive glacier melting during the last deglacial than the non-glacier-fed mega-lakes that developed in response to the early–middle Holocene rainfall maximum. We suggest that they were formed by melting glaciers, and therefore glaciers had major impacts on long-term lake evolution in the NWTP.