A 1000-year hydroclimate record from the Asian summer monsoon-Westerlies transition zone in the northeastern Qinghai-Tibetan Plateau

The Asian summer monsoon (ASM) and the Westerlies confront one another along the eastern margin of the Qinghai-Tibetan Plateau (QTP) in the mid-latitude Asia, resulting in a semi-arid transition zone. Potential expansion of aridity in the region will increase dust sources and threaten the densely populated east. Predicting regional hydroclimate changes in a warming climate, therefore, is invaluable for stakeholders. However, our understanding of the sensitivity of regional hydroclimate to temperature changes is limited, in part due to a lack of historical records. In this study, we reconstruct hydroclimate changes in the transition zone over the past millennium, based on the sediment organic contents and its stable carbon isotopes, from the Xiligou Lake in the northeastern QTP. We find that the lake basin was humid during part of the previous cold and warm anomaly, namely, the Little Ice Age and the Medieval Warm Period. This “bimodal pattern” was likely due to an alternation of the ASM and Westerlies as moisture suppliers. Subsequently, we find that the lake basin experienced a short-lived high stand event during the 1920s, superimposed on a wetting trend since 1850 AD. The event was likely caused by meltwater input and its demise can be partially attributed to the excess water demand from human activities. Our finding suggests that the configuration of circulations is likely to play an important role in directing the hydroclimate changes in the ASM-Westerlies transition zone, and additional evaluation should be made on the impact from increasing human activities.