Hydrogen isotopic compositions of long-chain leaf wax n-alkanes in Lake Qinghai sediments record palaeohydrological variations during the past 12 ka

摘要

Lake Qinghai, the largest saltwater lake in China, is located on the northeastern Qinghai-Tibetan Plateau. The lake sediments record the climatic variation and response to global climate change on the plateau. Numerous studies of the lake have been conducted, but various opinions remain regarding the palaeoclimatic conditions for the lake since the Last Glacial Maximum, especially the palaeohydrological conditions for the northeastern plateau in the early Holocene. Here, we discuss the hydrogen isotopic composition (delta D) of long-chain leaf wax n-alkanes for studying the hydrological changes in the lake since the Holocene. The results show that, on the northeastern Qinghai-Tibetan Plateau, C-31 delta D values were quite negative (avg. -202 +/- 4%) in the early Holocene (8-12 ka), indicating a strong monsoon and greater precipitation during that period. During 8-4 ka, C-31 delta D values gradually became more positive, indicating that the monsoon gradually weakened and precipitation gradually decreased. The C31 dD values were more positive in the late Holocene, with a mean value of -186 +/- 3%, showing that the regional monsoon weakened and the amount of precipitation was low. In addition, C-31 dD values indicated large amounts of precipitation in the early Holocene, but the C-29 delta D values during the same period were significantly more positive than C-31 due to a large contribution from aquatic plants. Therefore, the water level of the lake was low in this period, which could be related to strong evaporation of the lake water because of the high temperature in the early Holocene. Our study clarifies the changes in the monsoon and precipitation in the northeastern Qinghai-Tibetan Plateau and it provides a new estimate of the water level variation in Lake Qinghai in the early Holocene. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.