A note on circulation of the East China Sea

Abstract

The East China Sea lies over a wide continental shelf off the coast of China. Just like its neighbouring areas Bohai Sea and Huanghai Sea, the major part of the East China Sea is of a shallow water area, its mean depth being about 370 m. On the average, the annual discharge of fresh water into Bohai Sea, Huanghai Sea and the East China Sea is about 1.5  8, and among these, about 80~o is discharged into the East China Sea, the Changjiang River alone accounts for about 9 x 10nm3/year. Mixed with this large amount of fresh water the coastal water is of low salinity in this area. This Coastal Water System flows, generally, from north to south. Off the outer margin of the continental shelf, a powerful flow characterized by high temperature and high salinity and known as the Kuroshio moves from south to north, then to NE. Therefore, hydrographically, circulation of the East China Sea and its adjacent seas consists of a mesoscale cyclonic gyre with less saline current on the coastal side, warm and saline Kuroshio on the outer side. The characteristics of these two current systems are verydistinct; and the area these two current systems meet is called "front", where all the interactions (including mixing, diffusion, intrusion, etc.) of these two current-systems (hence two water mass-systems) produce the complicated hydrographic conditions of the East China Sea and its adjacent seas (Bohai Sea and Huanghai Sea). The complicated nature of the coastline and bottom topography, the seasonal variation of the prevailing winds, the changing of the discharge of the fresh water, etc. also contribute much to the distributions and variations of the hydrographic conditions of the East China Sea and its adjacent seas. The fore-mentioned two types of current system and hence two different water systems may further be sub-divided into six original water masses: 1) Coastal Water (of the East China Sea); 2) Huanghai Sea (Cold) Water mass; 3) Kuroshio Surface Water mass; 4) Kuroshio Subsurface Water mass; 5) Kuroshio Intermediate Water mass; and 6) Kuroshio Deep and Bottom Water mass. The Changjiang Diluted Water (mass) may be considered as a special kind of Coastal Water mass (of the East China Sea). Unlike the latter which generally flows from north to south, the Changjiang Diluted Water flows in the summer months from its estuary to NE and heads for the Cheju Island. Huanghai Sea Cold Water mass is located in the central part of Huanghai Sea, only its southern tip extends to the northernmost part of the East China Sea. This water mass, formed locally