Buoyancy-forced circulations around islands and ridges
Additional Document Info
Observations, theory, and modeling studies indicate that dominant components of both the upwelling and downwelling limbs of the thermohaline circulation take place near boundaries and in regions of steep and/or rough topography. Analytic and numerical results are used here to show that the interaction of upwelling regions with lateral boundaries fundamentally alters the resulting large-scale circulation compared to cases of open ocean upwelling. For narrow upwelling regions, viscous fluxes emerge as a leading term in the potential vorticity budget. The strong horizontal recirculation gyres that are found for sub-basin-scale open ocean upwelling (beta -plumes) are replaced by weak, unidirectional how into or out of the region of vertical motion. If the upwelling is located near an island or mid-ocean ridge, potential vorticity budgets require that a strong, large-scale recirculation develop around the topography, sometimes far from the region of mixing. The resulting boundary layers provide an important dynamic link between the large-scale horizontal components of the thermohaline circulation and the small-scale regions of strong vertical motions.