EFFECTS OF TOPOGRAPHIC STEERING AND AMBIENT STRATIFICATION ON OVERFLOWS ON CONTINENTAL SLOPES - A MODEL STUDY

The three-dimensional flow structures of cold dense overflow water on continental slopes with and without along-slope topographic variations and ambient slope water stratification are investigated, using a thre e-dimensional numerical ocean model. We discuss the effects of topogra phic steering and ambient stratification on the downslope transport of dense overflow on continental slopes. A constant upstream inflow of d ense water is specified at the upper edge of the slope that represents an overflow from a marginal sea. We present the numerical simulations for overflow plumes in the presence of three topographic features: a cross-slope canyon that leads from the coast to the deep ocean, a cros s-slope ridge, and a seamount. We compared the numerical results with the previously published results of overflow plumes on a uniform slope without ambient water stratification. In the presence of a canyon, a portion of the dense water descends into the canyon, forming a bottom- trapped plume that flows offshore along the right side (facing the oce an) of the canyon. The numerical result indicates that intensive mixin g and entrainment occur in the canyon plume. The remainder of the over flow flows across the canyon and keeps descending on the slope while b eing deflected to the right-hand side of the inflow. In the presence o f a cross-slope ridge, part of the water is blocked by the ridge and t he flow is confined along the left side of the ridge. The remaining po rtion of the plume water flows over the ridge toward the right-hand si de of the inflow. The presence of a canyon or a ridge significantly en hances the downslope transport of dense water compared with the unifor mly sloping bottom case. A seamount does not affect the cross-isobath transport of dense water as much as does a canyon or a ridge. A seamou nt does influence the mixing, entrainment, and the plume trajectories. Ambient slope water stratification has significant influence on the m ixing and cross-slope penetration of the overflow plumes. It has hinde red the downslope penetration of the plumes as a result of enhanced mi xing and entrainment when the plumes encounter deep denser water.