Hydrochemical characteristics and paleoclimate changes recorded from Sugan Lake on the northern boundary of Tibetan Plateau since mid-Holocene

Abstract

The Qaidam Basin, located in the northern Tibetan Plateau, is one of the three largest interior basins in China. It is surrounded by Kunlun, Altun and Qilian mountains with arid climate, sparsely vegetated landscape and a fragile ecological environment. Investigations on Holocene climate variations in this northern part of the Tibetan Plateau are essential for a better understanding of regional climate dynamics. A mid-Holocene sediment record from Sugan Lake in the Qaidam Basin was investigated using the grain size, mineral, total organic matter content (TOC), C:N ratio (C/N) and element analyses. A depth-age model since ∼ 7750 cal a BP had been made based on 8 AMS 14C data after taking out 2200 years carbon reservoir effect. SO42--type water and sparse terrestrial vegetation with considerable evaporation caused by high temperature during the Holocene Megathermal Maximum were recorded from ca. 7750 to 5800 cal a BP. From 5800 cal a BP, hydrochemical characteristics shifted dramatically to the Cl-type, while aeolian activities intensified concurrently. A higher lake level with low evaporation/precipitation ratio as the result of cool and wet conditions were inferred between 5800 and 3580 cal a BP when the EASM weakened and westerly jet intensified. Colder and drier conditions were recorded probably due to the strengthening of the mid-latitude westerly circulation after 3580 cal a BP. However, the EASM probably prevailed shortly at 3580 ∼ 3000 cal a BP and 1800 ∼ 810 cal a BP, respectively. Cold/dry, cold/wet and cold/dry Little Ice Age fluctuation climate conditions and aeolian activities with risen lake level and diluted water were inferred from 580 to 280 cal a BP.