Abstract:

In situ observation and satellite images show that Pearl River plume axis extends either alongshore between the upwelling off the Guangdong coast and in the Taiwan Bank or offshore in the northeastern South China Sea (SCS), depending on the upwelling intensities. Numerical model is set up to reproduce the upwelling processes and the areal extent of the Pearl River plume surrounding the upwelling areas. Model experiments are conducted to examine the effects of wind strength and baroclinicity on the upwelling and the corresponding pathway and freshwater transport of the Pearl River plume. The freshwater primarily transports alongshore, passing through the two separated upwelling regions in the initial stage of upwelling off the Guangdong coast, while it primarily transports offshore when the upwelling is fully-developed. The plume trajectory is modulated by the upwelling processes, related to the forcing agents. The baroclinicity is important to intensify the horizontal velocity at the upwelling front and freshwater transport in the northeastern SCS. The freshwater flux is decomposed into advection, vertical shear and tidal pumping components. The advection is the dominant contribution to the freshwater flux. As the upwelling off the Guangdong coast develops, the relative high pressure gradient zone moves offshore, because of the offshore Ekman transport and the shift of the upwelling front. The freshwater is thus brought offshore till east of the Taiwan Bank. When the plume water is transported to the outer-shelf, it could be further entrained into eddies, allowing its export to the open sea.