Restrictions on deep flow across the shelf-break and the role of submarine canyons in facilitating such flow

The shelf-break acts as a separator between the coastal ocean and the open ocean. Circulation (particularly deep near-bottom flow) is restricted from crossing the bathymetry. Eddies become elongated in the region of the shelf-break restricting exchange. An estimate of the horizontal eddy diffusivity over the shelf-break of less than 10 m(2) s(-1) is found from a numerical model. Various mechanisms are responsible for the weak cross-iso-bath flow that does occur. One is the increase of the Rossby number over small-scale topography such as submarine canyons. Along-shore flow (in the direction opposite to Kelvin wave propagation) generates upwelling through submarine canyons. A review of upwelling through submarine canyons is given. The deep cross-shelf flow generated by the canyons is shown to be Lis significant as the wind-driven upwelling in sonic regions. Examples for the reduction of flow across the shelf-break and for upwelling through canyons are taken from the West Coast of Vancouver Island.