Vegetation History And Precipitation Changes In The Ne Qinghai-Tibet Plateau: A 7,900-Years Pollen Record From Caodalian Lake

The northeastern Qinghai-Tibet Plateau is strongly influenced by the East Asian summer monsoon (EASM), the Indian summer monsoon (ISM) and the westerlies. However, how these various circulation systems interacted in the region during the Holocene, and the nature of the associated environmental impacts, are unclear and even controversial. Here we present a high-resolution pollen record from Caodalian Lake since 7.9 ka (1 ka = 1,000 cal yr BP), which is used to reconstruct the regional vegetation history and climatic changes. In addition, we use a novel procedure for pollen-based quantitative paleoclimatic reconstruction to characterize the evolution of precipitation at Caodalian Lake and nearby Qinghai Lake. The results suggest that mean annual precipitation (P-ann) is the most significant factor controlling the fossil pollen record at both sites, and the P-ann reconstructions are well correlated with each other (r = 0.72, p < 0.001). A synthesis of the P-ann records from the two sites indicates that the precipitation in the region began to increase before 10 ka, reached a maximum during 10-5 ka, and gradually decreased thereafter. We propose that the pattern of precipitation evolution in the Qinghai Lake basin resulted from the combined effects of the ISM and EASM, with a precipitation maximum of 10-7 ka for the ISM and 7-5 ka for the EASM; both systems contributed to the regional precipitation maximum during 10-5 ka. Our well-dated and unambiguous P-ann record also provides the opportunity to reconcile paleoenvironmental reconstructions derived from different paleoenvironmental proxies from the Qinghai Lake basin.