Holocene climatic changes revealed by aeolian deposits from the Qinghai Lake area (northeastern Qinghai-Tibetan Plateau) and possible forcing mechanisms

Previous palaeoclimatic studies in the northeastern Qinghai-Tibetan Plateau (NETP) during the Holocene, mainly using lake sediments, have deepened our understanding of the climatic system in this remote region. The timing and forcing mechanisms of climatic change in this region are still controversial, however. Aeolian sand and silt deposits, which are widely distributed in the NETP, can be readily dated by optically stimulated luminescence (OSL) techniques and reveal the sensitive response of the landscape to climatic change. In this study, aeolian sand and loess at six sites around Qinghai Lake were studied to reconstruct millennial-scale climatic changes during the Holocene. Multiproxy data along with 24 OSL age determinations show that low effective moisture and aeolian activity occurred at c. 13 ka, 10-9.1 ka, and 8.9-7.8 ka. Periods of greater effective moisture may have occurred at similar to 11 ka and 9 ka, and there is evidence for a previously undocumented wet climate at 4-3 ka. These results show that millennial-scale Holocene palaeoclimatic changes in the NETP cannot be explained simply as direct responses to changes in monsoon precipitation forced by summer insolation. We suggest that changes in effective moisture were determined by the balance between monsoon-induced rainfall and evaporation loss (mainly controlled by temperature). Thus, climatic change in the NETP may have been influenced by complex interactions between the monsoon circulation and local convection/ evaporation effects, in addition to large-scale change in the Asian monsoon and the westerlies.