Determining key upstream convection and rainout zones affecting δ18O in water vapor and precipitation based on 10-year continuous observations in the East Asian Monsoon region

An increasing number of studies have recognized the crucial impact of upstream convective activities and rainout processes on the stable isotopic composition of precipitation (δ18Op) and water vapor (δ18Ov) at mid and low latitudes. However, it is difficult to precisely identify the upstream convection and rainout zones using the common method based on the spatial distribution of time-lagged temporal correlation. Using a 10-year continuous high-resolution δ18Ov and δ18Op dataset at Nanjing (southeast China), the longest record of this kind, we develop an improved time-lagged correlation method for Key Upstream Convection Zones Identification (KUCZI). Utilizing this method, we find that summer δ18Ov and δ18Op at Nanjing are primarily controlled by the convective activities and rainout processes along the moisture transport pathway from the Maritime Continent (MC), via the Indo-China Peninsula and South China Sea (ICP_SCS), to Southeast China (SEC), particularly over SEC. Contrary to the conclusion of many existing studies, there is a possibility that the Indian Ocean is not a major convection zone affecting δ18Op and δ18Ov at Nanjing. Our results indicate that we may need to reconsider the role of the Indian Ocean on the paleoclimate interpretation of stalagmite δ18O records in the East Asian Monsoon (EAM) region. •A 10-year isotopic observation of δ18Ov and δ18Op was performed at Nanjing.•A method was developed to identify the key upstream convection zones affecting δ18O.•Convection and rainout effect along the moisture transport pathway control the δ18O.•Convection processes over the Indian Ocean have little impact on δ18O at Nanjing.