On subinertial flow in submarine canyons: Effect of geometry

Shelf break canyons on the west coast of Canada and the United States have been observed to be regions of enhanced upwelling during southward currents compared to the surrounding shelf break. Most shelf break canyons from Oregon north cross only part of the continental shelf cutting from the shelf break toward the coast but end on the continental shelf well below the mixed layer. Juan de Fuca canyon, on the other hand, cuts the continental shelf from the slope to, and actually continues into, the Strait of Juan de Fuca. This difference in geometry has a very strong effect on the subinertial flow around the canyon. Model canyon shapes, which include convergent bathymetric contours, are constructed and motivated for Juan de Fuca canyon and a typical shelf break canyon. Geostrophic analytic solutions show that the in‐canyon flow in Juan de Fuca canyon is generated by first‐order geostrophic dynamics, whereas in the majority of canyons, of which Astoria is an example, in‐canyon flow is generated by higher‐order effects. This difference is postulated to lead to the observed, very deep upwelling over Juan de Fuca canyon compared to more moderate, episodic upwelling over Astoria canyon.