The influence of a steady baroclinic deep ocean on the shelf

Abstract

The degree to which a baroclinic deep ocean could be responsible for the mean flow on the shallow continental shelf is examined using steady, boundary forced models which incorporate bottom friction. One set of models, for a vertically well mixed shelf, includes the horizontal advection of density. The second set of models comprises a three-layer model without and a two-layer model with interfacial friction. It is found that near bottom flow has a short cross isobath scale due to the steep continental slope and consequently that the deep oceans lower water column could not be responsible for the observed mean flow. The cross isobath scale of flow in the upper deep ocean is predominantly determined by the oceans velocity profile. In a barotropic or near barotropic flow the upper water column follows the near bottom flow and therefore has little influence on the shelf. A surface intensified deep ocean flow is able to cross isobaths until it encounters the bottom. If deep ocean flow is confined to a surface layer thinner than the depth at the shelf break it could be responsible for the observed flow. The depth scale for velocity and density over the slope in the Mid-Atlantic Bight is generally larger than the shelf break depth and consequently it is concluded that the steep continental slope "insulates" this particular shelf from baroclinic deep ocean influence and therefore that the observed shelf flow is not of oceanic origin. Using oxygen isotope data, Chapman et al. (1986) found that the Scotian shelf is the major source of Mid-Atlantic Bight shelf water. Their barotropic modeling results are extended to show that a baroclinic deep ocean also acts to hold shelf water on the shelf.