A 1.68 Ma organic isotope record from the Hetao Basin, upper reaches of the Yellow River in northern China: Implications for hydrological and ecological variations

Quaternary hydrological and ecological variation of the paleolakes, intermittently developed within the Hetao Basin in North China, is not only closely related to the evolution of the Yellow River discharge but also influenced by the East Asian summer monsoon. However, long-term variability history of hydrology and ecology of these lakes, as well as the driving mechanism, is still poorly understood. Here, we reconstructed the hydrological and ecological variation of these paleolakes since the past similar to 1.68 Ma based on the interpretation of multi-geochemical proxies of the organic matter including TOC and TN concentrations, C/N ratios, and the delta C-13 and delta N-15 values. The results show that the lakes in the Hetao Basin are dominated by relative low lake level, deteriorated aquatic plant abundances and low phytoplankton productivity during the intervals similar to 1.47 to similar to 1.30 and similar to 1.17 to similar to 1.07 Ma, and similar to 0.68 to similar to 0.60 Ma, while relative high lake level with flourishing aquatic ecosystem and high aquatic productivity occurred from similar to 0.47 Ma to the last interglacial. Meanwhile, tectonically-driven relative height of the basin outlet, preventing the Yellow River water outflows the basin to widen the Yellow River channel in the basin, may be the key factor resulting in the significant rising of the water level of the paleolake formed within the Hetao Basin from similar to 0.47 Ma to the last interglacial.