A NUMERICAL STUDY OF DENSE WATER FORMATION AND TRANSPORT ON A SHALLOW, SLOPING CONTINENTAL-SHELF

The circulation and transport of dense water generated by an idealized coastal polynya is studied using a three-dimensional primitive equation model. Starting with a homogeneous, quiescent ocean, a constant negative buoyancy flux is imposed at the surface over a half-elliptical region adjacent to the coastal boundary on a gently sloping continental shelf. The flow response can be divided into the following three phases: geostrophic adjustment, instability, and offshore eddy transport. During geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there. Eventually, the flow at the leading edge of the forcing region (relative to Kelvin wave propagation) becomes unstable and a train of counterrotating eddies develops. These eddies then form a complex three-dimensional flow field and rapidly transport dense water offshore, across isobaths. The density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore. The results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope. Eddy scales and velocities are consistent with observations in the Arctic. The results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas.