Overflows and Upper Ocean Interaction: A Mechanism for the Azores Current

Shinichiro Kida, Ph.D., 2006
Jiayan Yang, Jim Price, Advisors

The oceanic response to overflows is explored using a two-layer isopycnal model. Overflows are a major source of the dense water of the global deep ocean and when they enter the open ocean as dense gravity currents down a continental slope, they entrain upper oceanic water. The upper ocean must balance this mass loss and the vortex stretching associated with this entrainment. Overflows represent an intense localized mass and PV forcing for the upper ocean.

The simulations show that entrainment forces a cyclonic circulation along bathymetric contours in the upper layer and when baroclinic instability develops, a double gyre also forms near the strait. These circulations are topographic beta-plumes and have transports as large as the overflows. For the Mediterranean overflow, the topographic beta-plume becomes a basin scale flow and establishes two trans-Atlantic zonal jets, analogous to the Azores Current and the Azores Countercurrent. The presence of eddies near the steep slope near Cape St. Vincent allows the topographic beta-plume to connect to the open ocean. < /p>

This thesis shows that overflows can induce a significant circulation in the upper ocean, and for the Mediterranean overflow, this circulation is a basin scale flow.