Influences of tides on shelf circulation in the northeastern South China Sea during summer

Tides have significant effects on material and energy transports over the continental shelf. A mooring system located in the shelf region of the northeastern South China Sea observed strong and weak mean currents during the spring and neap tides in summer, respectively. The mechanism leading to this difference is investigated by using a three-dimensional circulation model. We find that the impact of tides (TI) on currents exhibited as current components opposing wind-driven circulation play an important role. The TI current components are stronger than the tidal residual currents in summer when vertical stratification enhances the tidal rectification. Tides can affect pressure gradient by modifying sea surface height on the shelf, while in shallow and shelf break regions, the non-linear advection and vertical diffusion become significant in momentum equations attributable to the interactions of tidal currents, bottom topography and water column stratification. Consequently, the along-shelf volume transport is reduced by about 21.6% due to the TI current components and only by about 6.1% due to the tidal residual currents. This study highlights the importance of both tidal mixing and tidal rectification in regulating shelf circulation in the northeastern South China Sea.