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 (δ¹⁸O_p) and water vapor (δ¹⁸O_v) 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 δ¹⁸O_v and δ¹⁸O_p 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 δ¹⁸O_v and δ¹⁸O_p 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 δ¹⁸O_p and δ¹⁸O_v 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.