The influence of a submarine canyon on the wind-driven downwelling circulation over the continental shelf

The response of a coastal ocean model, simulating a typical Eastern Boundary system, to downwelling-favorable winds with and without the presence of a submarine canyon is studied. Three contrasting bathymetric configurations, considering shelves with different depth and slopes, are evaluated. Experiments without a submarine canyon represent the well-known downwelling circulation and cross-shore structure with a downwelling front and the development of frontal instabilities generating density anomalies in the bottom layer. The presence of the submarine canyon drives important changes in cross-shore flows, with opposing velocities on either side of the canyon. Onshore (offshore) and downward (upward) velocities develop in the upstream side of the canyon in the time-dependent and advective phases. Instabilities developed and are modified principally downstream of the canyon. Overall, the net impact of the canyon is to enhance offshore and downward transport. However, particle tracking experiments reveal that particles can become trapped inside the canyon in an anticyclonic circulation when the particles pass the canyon over the continental slope or when particles inside the canyon are affected by downwelling conditions. Overall, ~20–23 % (~15–18 %) of particles released directly upstream (in the canyon) at mid-depths become trapped inside the canyon until the end of the simulations (15 days).