Climatic implications of hydrologic changes in two lake catchments on the central Tibetan Plateau since the last glacial

The numerous and widespread lakes of the Tibetan Plateau (TP) constitute the largest group of alpine lakes on Earth. Some of the lakes are fed mainly by glacier meltwater and others by precipitation and groundwater. Past changes in the environments of these lakes differed because of differences in lake hydrological regimes and the complex pattern of climate change on the TP. Here we present records of scanning XRF, inorganic carbon (IC) concentration n-alkanoic acid average chain length (ACL) and percent aquatic inputs (Paq) in sediment cores from two non-glaciated lakes on the central TP (Dagze Co and Jiang Co), which span the past 19,000 years. We used these measures to investigate past changes in catchment hydrology, climate and environment. Variations in the concentration of Ti and other lithogenic elements at the two sites were influenced mainly by surface runoff, which is supported by the variation of IC, Ca/(Al, Ti, Fe) (reflecting authigenic carbonate precipitation), Rb/Sr (a chemical weathering proxy), and ACL and Paq. We attribute variations in surface runoff to changes in the precipitation/evaporation ratio, caused by the pattern of climate change on the central TP since the late Pleistocene. During the late Pleistocene, stronger runoff (indicated by higher Ti, higher Rb/Sr and Paq, lower IC, Ca/(Al, Ti, Fe) and ACL) likely resulted from lower temperatures. Lower runoff during the Holocene may reflect intensified evaporation caused by higher temperatures. Comparison with records from glaciated lakes in the region reveals opposite trends in catchment hydrology. Overall, our results suggest that since the late Pleistocene the central TP was influenced mainly by the Indian Summer Monsoon.