Water mass formation and seasonal variations in the Yellow and East China Seas and effect of the wind and transport variation
The Yellow Sea and East China Sea is a wide shelf area where mixing is active between saline Kuroshio water and fresh coastal and shelf water. The water mass is, thus, very interesting to study in this area. Water masses are determined based on relatively long term NODC temperature and salinity observations using a statistical cluster analysis. Results shows strong seasonal variations of the water masses delineated, the temperature and salinity range, and the distribution of each water mass. In summer, fresh and warm surface water separates from the other water masses. In winter, water masses are separated horizontally and not vertically. The POM based Yellow Sea Model is utilized to study the behavior of warm saline water sources (Kuroshio and the Taiwan Warm Current: TWC) and the wind effect by adding an imaginary tracer at the Kuroshio and TWC entrance. The three year (1994-1996) model run is analyzed excluding the six-month spin up for both the with and without wind cases. Results shows the Kuroshio water flows into the Yellow Sea and the Korea Strait whether there is wind or not. TWC water covers mainly the surface layer of the northwestern half of the East China Sea. Strong winter northwesterly winds push the flow pattern more northwest-ward in the shape of intermittent intrusions into the Yellow Sea due to relaxation of the wind. Summer monsoon, on the contrary, supports a northeast-ward flow pattern. Horizontal salt flux is investigated based on the model salinity and velocity field. The Kuroshio main stream area shows strong salt influx. Along the Chinese coastal area, fresh water influx is dominant. The salt flux is dominant in the surface layer. Major water mass formation mechanisms in the study area are the surface cooling, fresh water addition at the surface, and advection of the open ocean water. Wind affects mostly the surface layer and horizontal mixing at the boundary of the Kuroshio and Taiwan Warm Current.