Flow near submarine canyons driven by constant winds

Circulation over coastal submarine canyons driven by constant upwelling or downwelling wind stress is simulated and analyzed with a primitive equation ocean model. Astoria Canyon, on the west coast of North America, is the fo cus of this study, and model results are consistent with most major feature s of mean canyon circulation observed in Astoria Canyon. Near-surface flow crosses over the canyon, while a closed cyclone occurs within the canyon. U pwelling prevails within the canyon and is larger than wind-driven upwellin g along the adjacent shelf break. Water rises from depths reaching 300 m to the canyon rim and, subsequently, onto the adjacent shelf. Onshore flow wi thin the canyon is driven by the onshore pressure gradient force, due to th e free surface slope created by the upwelling wind, and is enhanced by the limitation to alongshore flow by the canyon topography. Density gradients l argely compensate the surface slope with realistic stratification, but cont inual upwelling persists near the edges of the canyon. Within the upper can yon (50-150 m below the canyon rim) a cyclone is created by flow turning in to the canyon mouth, separating from the upstream edge, and advecting towar d the downstream rim. Below this layer the cyclone is created by vortex str etching due to the upwelling. Downwelling winds create nearly the opposite flow, in which compression and momentum advection create a strong anticyclo ne within the canyon. Momentum advection is found to be important both in c reating strong circulation within the canyon and in allowing the surface fl ow to cross the canyon undisturbed. Model results indicate that Astoria-lik e submarine canyons produce across shore transport of sufficient volume to flush a continental shelf in a few (2-5) years.