Holocene lake level variations of Longmu Co, western Qinghai-Tibetan Plateau

Longmu Co is surrounded by conspicuous regressive shorelines attesting to high-water levels in the past. In this study, we dated paleoshoreline sediments around the lake using optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL) and radiocarbon dating, then explored the forces that drove Holocene lake level variations. We found that: (1) OSL/ IRSL ages are consistent with geomorphic sequences and some extant cosmogenic and U/Th shoreline ages. However, inorganic evaporite crust 14 C ages are much older than corresponding OSL/IRSL ages due to varying lake reservoir effects and should be used with caution; (2) The highest lake levels of Longmu Co (similar to 160-145 m above present) lasted from similar to 12.8 to similar to 11.3 ka. Two periods of abrupt lake level declines occurred at similar to 11.3 and similar to 7.4 ka (lake level dropped similar to 44 and similar to 45 m, respectively), with a gradual regression of similar to 18 m between these two intervals. The lake expanded moderately from similar to 7 to 5.5 ka, then declined once more after similar to 5.5 ka, with this regression accelerating during the last similar to 1.5 ka; (3) The deglacial lake level transgression was likely due to glacier melt waters. The Indian Summer Monsoon reached the Longmu Co watershed and brought precipitation during the early Holocene. Middle to late Holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration.