Late Quaternary lake level variations of Mabu Co-Gala Co, southern Tibetan Plateau, and the impacts on early inhabitants

Lakes on the Tibetan Plateau (TP) play a major role in the regional hydrological cycle and underpin vital ecosystem services. However, the long-term lake evolution and underlying mechanisms, especially on the exorheic southern TP, remain unclear. Here, we reconstructed the lake level variations of Mabu Co and Gala Co on the southern TP through detailed paleo-shoreline dating using post-infrared infrared stimulated luminescence (pIRIR) signals of K-feldspar single grains, and explored the driving forcings based on a comparison of paleoclimate records and geomorphological analysis. The results show that a unified paleolake at Mabu Co and Gala Co at a level ~20 m above the modern level (a.m.l.) of Mabu Co developed during the late MIS 3 (35.9±1.9-29.1±1.4 ka) in response to increased glacial meltwater and Indian summer monsoon (ISM) rainfall. Under intensive glacier melting, the paleolake reached its maximum level (~29 m a.m.l.) and area (190 km2, ~22 times larger than the modern areas of Mabu Co and Gala Co) during the last deglacial (16.8±1.0-13.6±0.7 ka) and began to outflow, which triggered incision and lowering of the spill-point. The lake level showed an overall decreasing trend since the last deglacial largely influenced by the lowering of the spill-point. During the last deglacial-early Holocene (12.7±0.6-9.8±0.6 ka), a high-stand lower than that in the previous stage (~24 m a.m.l.) was maintained by the strengthened ISM and glacial meltwater. In the mid-Holocene (8.7±0.9-4.1±0.3 ka), the paleolake experienced two rapid lake level drops in response to the weakening events of the ISM. The exposed shoreline terrace between the two lakes following the lake level drop after ~6 ka provided an ideal living surface for the inhabitants at the Mabu Co site during 4.5-4.0 ka. We found that glacial meltwater and lake spillover processes, apart from the ISM, have exerted great impacts on the hydrological history of Mabu Co and Gala Co. The paleolakes have provided critical resources for humans at the Mabu Co site living in the alpine anoxic environment. Additionally, we suggest that lakes with low spill-points adjacent to exorheic basins on the southern TP should be given more attention regarding flooding hazard risks against increasing precipitation and glacial meltwater in the future.