We investigate ventilation in the South China Sea (SCS) based on a recently developed framework for annual subduction/obduction in monsoon-dominated oceans. It is found that subduction occur in winter, and it was greatly weakened by ~58% due to the summer monsoon. Furthermore, there is a second obduction window opened up during the summer monsoon period, besides the winter obduction window.

The winter subduction is concentrated in two narrow regions: one is located in the northern SCS and the other in the eastern SCS from 10°N to 15°N. The winter obduction distributes widely in two areas: the northeastern SCS and the area south of 10°N, while the summer obduction occurs primarily near the Vietnam. The key factors regulating subduction/obduction and their variability at different areas are different: the lateral induction term is the key contributor for subduction in the northern SCS; however, for the subduction in the eastern SCS and the obduction process, the vertical pumping term is dominant. Furthermore, the subducted (obducted) water in the SCS would penetrate into (come from) the subsurface ocean at the depth ~ 100m after (before) one year.