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

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 hei ght that follows variable bottom topography under constant vertical grid sp acing. An idealized continental slope of constant bottom slope is considere d, including parallel channels that run perpendicular to main isobaths. The ocean is initially homogeneous and at rest. Forcing is due to a layer of d ense water prescribed along the upslope boundary. When the channel aspect r atio (ratio of width to depth) exceeds the main bottom slope, dense water i s carried downslope by narrow channel plumes centered along the channel axe s. Owing to a small internal Rossby radius less than the channel width the plume dynamics are governed by a geostrophic balance across the channels. I nteraction of adjacent channel plumes leads to complex bottom-parallel circ ulations. The net downslope density Aux resulting from these circulations e xceeds that of viscous (ageostrophic) flow of dense water developing withou t channels. When the channel aspect ratio is less than the main bottom slop e, the descent of dense water is dominated by viscous flow. Narrow geostrop hic circulation patterns along channels, superimposed on the mean flow, how ever, induce advective entrainment of lighter ambient water across the lead ing density front of descending water. As a result of this, the net downslo pe density flux is reduced as compared to that without channels. Sensitivit y studies reveal that the channel-modified dynamics are independent of the magnitude of the eddy viscosity.