A numerical study of three‐dimensional dense bottom plumes on a Southern Ocean continental slope

Abstract

Three‐dimensional features of dense bottom plumes flowing over continental slopes, with or without along‐slope topographic variations, are investigated by simulating the evolution of a density front at a Southern Ocean continental shelf break, using a three‐dimensional, primitive equation numerical model with a second‐order turbulence closure scheme embedded. The focus of our investigation is the role of topography in determining mixing and the offshore transport of dense shelf water during the transient adjustment process of a density front over a continental slope. We compare and discuss the numerical simulations for two cases: a uniform shelf and slope case and a case with a canyon that leads from the coast to the deep ocean crossing the shelf and the slope. The numerical simulations indicate that baroclinic instability, planetary rotation, bottom friction, and topography play major roles in determining the surface and bottom plume formation, the growth and penetration depth of the bottom plumes, and the characteristics of water mass on the slope. Mesoscale eddies play a fundamental role in transporting mass, heat, and salt from shelf to deep ocean. The effects of the depth and width of the canyon are examined with two more experiments. The presence of a wide and deep canyon in the continental shelf and slope enhances considerably the drainage of coastal shelf water into the deep ocean.