Topographic steering of dense currents with application to submarine canyons

The influence of a submarine canyon on a dense bottom current flowing along the continental shelf is considered. It is shown that the front of the current moves forward with the Nof velocity, establishing a stationary plume parallel to the depth contours behind it. The stationary flow has a frictional transport directed downhill, perpendicular to the depth contours. This transport converges inside topographic depressions. Consequently, the heavy water accumulates in such areas and the current may change direction and flow inside the depression rather than along the depth contours. Submarine canyons can influence the along-shelf flow in this manner. A canyon that intersects the continental slope has the ability to channel dense water down to the deep sea. The rate at which water is drained from the along-shelf flow is determined from the canyon's geometry and the magnitude of bottom friction. If the along-shore transport upstream of the canyon exceeds the capacity of the canyon, the plume divides into two branches. A portion of the flow is then steered down into the canyon while the rest continues on the downstream side of it. The distribution of dense water inside the canyon is obtained analytically for a simplified description of bottom friction, as well as numerically for more complex friction parameterizations. The results are remarkably similar. This indicates that the downward flow is controlled by the topography and the magnitude of bottom friction rather than the choice of how friction is parameterized. (C) 2002 Elsevier Science Ltd. All rights reserved.