Effects of tides on freshwater and volume transports in the Changjiang River plume

Effects of tides on the Changjiang River plume are investigated using a numerical model of the East China and Yellow Seas. In the absence of tides, the buoyancy-driven coastal current downstream of the river mouth is a surface-trapped plume attached to the coast. In the presence of tides, however, the plume shifts away from the coast and features a bottom boundary layer. The freshwater transport by the coastal current accounts for only 35% of the Changjiang River discharge without tides but increases to 80% with tides. Tidal currents stabilize the plume bulge near the river mouth and force the plume water to move in the direction of tidal currents, thus increasing the downstream freshwater transport. In contrast, tidal residual currents are weak and make little contributions to the total freshwater transport. Tidal mixing reduces the plume's buoyancy but increases its thickness so that the freshwater transport is insensitive to the strength of turbulent mixing. Volume transport in the tidal-affected buoyancy coastal current exceeds the river discharge by 4 to 12 times, as opposed to 2-3 fold amplification in the plume without tides. Tidal mixing between the plume and ambient shelf waters produces higher salinity classes in the plume so that the volume flux in the downstream coastal current increases to discharge the freshwater released from the Changjiang River.