Advances in research of the mid-deep South China Sea circulation

The South China Sea (SCS) is a large marginal sea connecting the Indian and Pacific oceans. Under the factors of monsoons, strait transport, and varied bathymetry, the SCS presents a three-layer structure and strong diapycnal mixing which is far greater than that in the open ocean. Theoretical analysis and observations reveal that internal tides, internal solitary waves, and strong winds are the sources of the strong mixing in the northern SCS. A major consequence of the strong mixing is an active mid-deep circulation system. This system promotes exchange of water between the SCS and adjacent oceans, and also regulates the upper layer of wind-driven circulation, making the 3 dimensional SCS circulation clearly different from that in other tropical and subtropical marginal seas. The mass transport capacity of the mid-deep circulation has a substantial impact on marine sedimentation, the biogeochemical cycle, and other processes in the SCS. This paper summarizes the recent advances in mid-deep sea circulation dynamics of the SCS, and discusses the opportunities and challenges in this area.