Interplay between Asian monsoon and westerlies over Northern Tibetan Plateau in the past 26ka

Abstract:

The Asian summer monsoon (ASM) and the mid-latitude Westerlies are two major atmospheric systems influencing Tibetan Plateau. Recent findings at Lake Qinghai show the two systems interplay at glacial/interglacial scales. The climate effect of the monsoon and the Westerlies differs significantly. As the monsoon weakened and retreated gradually during the middle to late Holocene, the convergence zone between the monsoon and the Westerlies would shift correspondingly. However, it is unclear where and when the convergence zone is located on the TP. Lingge Co (88°36’E, 33°51’N) is currently located within the convergence zone between ASM and Westerlies in the Northern Tibetan Plateau (NTP). Sediment core at the lake covering the past 26 kyr would provide critical information on influence of ASM and the Westerlies and reveal their variation since the last deglaciation. We analyzed GDGTs, δ²H of sedimentary leaf waxes, δ¹⁸O of ostracod (Leucocythere mirabilis) , sediment grain size and loss on ignition to reconstruct changes in temperature, precipitation isotope ratios, lake water isotope ratios, lake water balance and productivity. The comprehensive records show that the climate was cold and dry during the last deglaciation (~26-12ka), with evident Heinrich 1 and Younger Dryas cooling events, suggesting that the NTP mainly influenced by the Westerlies. During the early Holocene, the climate was warm and wet mainly influenced by ASM. However, significant enrichment in δ²H at ~9-6ka and ~4.5-2ka, as well as increased water energy, reflects the intrusion of Westerlies into the NTP. These two periods are in line with the humid period in Westerlies dominant area. The Lingge Co records demonstrate interplay between ASM and the Westerlies on the NTP during the Holocene, which is critical to understand the mechanisms of climate changes in Tibetan Plateau since the last deglaciation.