Centennial-scale interplay between the Indian Summer Monsoon and the Westerlies revealed from Ngamring Co, southern Tibetan Plateau

The Asian summer monsoon and the mid-latitude Westerlies are major atmospheric circulation systems which influence the climate of the Tibetan Plateau (TP), and hence the water resources, ecology, and socioeconomic well-being of the region. The interplay between the monsoon and the Westerlies has been investigated on glacial–interglacial, millennial, and decadal scales. However, due to the scarcity of high-resolution climate records from the TP, there is a lack of information on the centennial scale, which is more closely related to the development of civilization. Here we present a decadal-resolution precipitation record covering the past ~3600 years from Ngamring Co in the southern TP. The record suggests the gradual weakening of the Indian Summer Monsoon (ISM) with multiple centennial-scale fluctuations, which are synchronous with temperature changes. Precipitation was relatively high during the Medieval Warm Period (MWP) and low during the Little Ice Age (LIA). A wet Roman Warm Period (RWP) and an abrupt dry spell at 2.8 ka are also identified. Comparisons suggest that an intensified Westerlies penetrated the southern TP during dry intervals, such as during the 2.8 ka event, ~1700–1450 cal yr BP, and the LIA; whereas an intensified monsoon prevailed during warm periods such as the MWP. The centennial-scale oscillations of precipitation in the southern TP during the late Holocene suggest the role of the Westerlies in regulating ISM moisture delivery to the region, which likely resulted from variations in the surface temperature of the North Atlantic together with solar activity.