Impact of multiple submarine channels on the descent of dense water at high latitudes

Abstract

A three‐dimensional numerical hydrodynamic model is applied to examine the impact of multiple submarine channels (<10 km across, <100 m deep), common to most continental margins of the ocean, on the descent of dense water at high latitudes. The model consists of an ocean bottom layer of constant height that follows variable bottom topography under constant vertical grid spacing. An idealized continental slope of constant bottom slope is considered, including parallel channels that run perpendicular to main isobaths. The ocean is initially homogeneous and at rest. Forcing is due to a layer of dense water prescribed along the upslope boundary. When the channel aspect ratio (ratio of width to depth) exceeds the main bottom slope, dense water is carried downslope by narrow channel plumes centered along the channel axes. Owing to a small internal Rossby radius less than the channel width the plume dynamics are governed by a geostrophic balance across the channels. Interaction of adjacent channel plumes leads to complex bottom‐parallel circulations. The net downslope density flux resulting from these circulations exceeds that of viscous (ageostrophic) flow of dense water developing without channels. When the channel aspect ratio is less than the main bottom slope, the descent of dense water is dominated by viscous flow. Narrow geostrophic circulation patterns along channels, superimposed on the mean flow, however, induce advective entrainment of lighter ambient water across the leading density front of descending water. As a result of this, the net downslope density flux is reduced as compared to that without channels. Sensitivity studies reveal that the channel‐modified dynamics are independent of the magnitude of the eddy viscosity.