Heton Shedding from Submarine-Canyon Plumes in an Arctic Boundary Current System: Sensitivity to the Undercurrent

Abstract

The lateral injection of dense outflow into an Arctic baroclinic current though a submarine canyon is examined using a three-dimensional nonhydrostatic numerical model. The oceanographic setting in this model retains essential features of the active outflow region from the Chukchi shelf to the Beaufort Sea. The coastal ocean mainly consists of a continental shelf and slope region indented by a submarine canyon. The ocean surface is partially frictional to account for the ice-exerted friction. A boundary current is bounded to the left by the continental slope and, in the most interesting cases, is bounded below by a reverse undercurrent. Dense water is released from the upper canyon and produces a sinking plume that follows the canyon axis seaward. As it approaches the maximum sinking depth, the subsurface plume moves out of the canyon and turns to the right to become a right-bounded undercurrent over the continental slope. The right turn generates anticyclonic vorticity. The sinking motion also induces a surface cyclone trapped over the canyon. If the centers of the top cyclone and subsurface anticyclone are sufficiently separated horizontally, the pair can form a self-propagating heton moving seaward from the canyon. Thus the heton shedding is an efficient way to produce halocline anticyclones that are known to populate the Beaufort Sea. Shedding is most active for fast release of dense water and if the maximum sinking depth is in the lower halocline. Heton shedding can occur in the absence of a boundary current. A unidirectional boundary current enhances heton shedding. An undercurrent provides background negative vorticity to the subsurface anticyclone and moves the anticyclone in the direction favorable for the seaward heton propagation. In consequence, the addition of an undercurrent facilitates much more efficient heton shedding.