Some Effects of a Seamount on Oceanic Flows

Abstract

To demonstrate some effects of a seamount an oceanic flows, we have considered a uniform, two-layer flow passing a right circular cylinder of arbitrary height in a rotating fluid. In the case of vanishing stratification, we first generalize previous results of low obstacles to an obstacle of finite height, and then show how the frictional regime provides a transition from partial to total blocking as the obstacle top approaches the surface. In the case of general stratification, we have discerned various dynamical regimes according to blockage of the flows, characterized by distinctive interface signatures. For example, as the obstacle top rises through the water column, the axisymmetric doming of the interface first gives way to a reduced fore-and-aft symmetry when the lower layer is partially blocked, then becomes a net depression when the lower layer is totally blocked, and finally returns to its unperturbed level as both layers become totally blocked. We have derived the critical stratification below which there may be overlapping Taylor columns, and hence possible ventilation of the lower layer if surface cooling occurs. For typical oceanic conditions, this critical stratification corresponds to a baroclinic deformation radius measuring about one-half of the obstacle radius. By generalizing the model results to a multiple-layer fluid, we have deduced mesoscale features similar to that observed over the Emperor Seamounts. When the model is applied to the Maude Rise in the Weddell Sea, it can explain the extensive ventilation of the water above the rise, with possible implications on the initiation and maintenance of the Weddell polynya.