资源环境科技发展态势分析平台

The precipitation changes on the northeastern Tibetan Plateau during the Holocene remain unclear due to discrepancies among different proxy records. We compared proxy records with the results from a transient simulation performed using the Kiel Climate Model forced by orbital variations, to analyse summer precipitation changes in this area during the Holocene (9.5-0 ka BP). The model results suggested increasing amounts of summer precipitation from 9.5 to similar to 6.2 ka BP and a persistent decline thereafter, which matched well with pollen records but was inconsistent with ostracod delta O-18 records. The Holocene climatic optimum lagged the Northern Hemisphere summer insolation maximum by similar to 3.5 ka, caused by the interplay between the East Asian summer monsoon (EASM) circulation and the mid-latitude westerlies. The ostracod delta O-18 values reflected the strength of the EASM circulation. A strong EASM circulation increased the transport of water vapour towards the northeastern Tibetan Plateau from the northwestern Pacific. Weakened mid-latitude westerlies increased the incursion of cold air masses into the northeastern Tibetan Plateau. During the early Holocene, relatively strong mid-latitude westerlies, resulting from an enhanced Arctic Oscillation, reduced summer precipitation on the northeastern Tibetan Plateau, in spite of a strong insolation-driven EASM circulation. The weakening EASM circulation and the strengthening westerlies together induced the decreasing trend of summer precipitation from the middle to late Holocene. In addition, summer precipitation variations were further modulated by sea-surface temperatures in the northwestern Pacific, through weakening the strength of the EASM.