Effects of a baroclinic current on a sinking dense water plume from a submarine canyon and heton shedding

Abstract

Ventilation of the Arctic halocline by dense water outflow from a submarine canyon is investigated in a nonhydrostatic numerical model with a rigid lid and an idealized shelf–slope topography appropriate for the Barrow Canyon in the Beaufort Sea. Dense water from the canyon descends on the slope and turns to the right, forming a bottom trapped plume. Anticyclonic eddies subsequently break away from the plume and enter the deep ocean. In the absence of an ambient current beyond the shelf break, the anticyclones are weak and have limited effects on ventilation. An offshore baroclinic current expedites the process. The boundary current acquires cyclonic vorticity from meanders at the canyon's mouth because of the potential vorticity constraint. The cyclonic vorticity enhances sinking of dense water along the slanted isopycnals in the baroclinic current. The sinking plume in turn reinforces the cyclonic vorticity. Subsurface anticyclones are generated during this process, and vortex pairs known as hetons form from subsurface anticyclones and surface cyclones. Hetons have self-propagating properties and, in the present setting, propagate seaward from the canyon. The anticyclonic vorticity in a heton is much stronger than that in a single vortex. The positive feedback mechanism and the production of hetons could ventilate the halocline and generate subsurface anticyclones in the Beaufort Sea. Efficient ventilation of the halocline could result from optimal matching of the density and inflow velocity of the dense water from the canyon and the baroclinic structure of the offshore current.