The role of vorticity fluxes in the dynamics of the Zapiola Anticyclone

The Argentine Basin in the South Atlantic Ocean is one of the most energetic regions in the ocean with complicated dynamics, which plays an important role in the global climate. A number of observations have discovered an intense anticyclonic gyre of barotropic circulation around the Zapiola Rise in the center of the basin. Theoretical studies have shown that the Zapiola Anticyclone represents an eddy-driven flow controlled by bottom friction. Recent advances in high-resolution global-ocean data syntheses, performed using NASA supercomputing facilities, provide realistic simulations of the circulation and the variability in the Argentine Basin. Using these simulations and satellite altimeter observations, we analyzed the vorticity balance of the Zapiola Anticyclone. Our results suggest the dominance of vorticity fluxes and the advection of the potential vorticity over a nonuniform bottom topography in determining the variability of the gyre, while the impact of the local wind stress is small. The divergence of the relative vorticity anomaly advection by eddies is found to be the most important contributor to the relative vorticity flux divergence influencing the variability of the Zapiola Anticyclone. Our results demonstrate that the relative vorticity influencing the variability of the anticyclone is mainly advected from the south where the northern branch of the Antarctic Circumpolar Current at the Subpolar Front is located.