Energy balance and momentum budgets due to the internal tides generated by a group of submarine canyons

A field multibeam survey discovered a group of regularly-spaced submarine canyons on the continental shelf in the northern South China Sea. However, they are not included in the bathymetry datasets commonly used by the oceanographic community. In this study, we employ a very-high-resolution (as fine as 54 m) numerical model that resolves these submarine canyons to investigate their impacts on the local internal tide generation and propagation. Results show that the barotropic to internal tidal conversion rate exhibits an alternating distribution on each flank of submarine canyons. Rotational direction of the tidal flow determines a positive conversion rate on the west flank and a negative rate on the east flank. The rough seafloor due to the submarine canyons does not appreciably change the dissipation of barotropic tides, but significantly affects the dissipation of internal tides, leading to an averaged dissipation rate of 1.2 x 10-9 W kg-1. Internal tides also induce a bottom intensified mean flow, which causes westward mean transport on the continental slope and a clockwise circulation inside each submarine canyon. The mean flow satisfies a momentum budget between the Coriolis force, pressure gradient and divergence of momentum flux of barotropic and internal tides. We highlight that the divergence of the pseudo-momentum flux of internal tides acts as a stress and is especially reinforced near the sea bottom and surface. Its effect on the sea surface is even comparable with moderate winds (& SIM;13 m s-1).

Automated summary

Submarine canyons on the continental shelf in the northern South China Sea have significant impacts on the generation and propagation of internal tides. The rough seafloor of these canyons affects the dissipation of internal tides and induces intensified mean flow and clockwise circulation inside each canyon.