The seasonal variation of shallow meridional overturning circulation in the South China Sea and the related dynamics

Abstract

The shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) contributes to the local heat redistribution. Most investigations focused on its annual mean structure but paid little attention to its seasonal variation. In this study, the products of Ocean General Circulation Model for the Earth Simulator (OFES) are used to study the seasonal variation of the SMOC in the SCS. Results indicate that the SMOC can be formed in both winter and summer, and its structure has a prominent seasonal variation. The SMOC is clockwise and appears between 9°N and 18°N in winter, while it is anticlockwise and confined to the southern SCS in summer. Related dynamics of the SMOC seasonal variation are further investigated. It is found that the winter monsoon is essential for the formation of the clockwise winter SMOC, and the buoyancy flux also contributes to the winter SMOC formation via influencing the mixed layer depth. Although the SCS conditions are dramatically changed in summer, the summer monsoon can still circulate the water around in the circuit of the anticlockwise summer SMOC. The monsoon is the primary driving factor that dominates the formation and seasonal variation of the SMOC in the SCS.