Intrinsic variability of the Antarctic Circumpolar Current: low-frequency fluctuations in the Argentine Basin flow

The dynamics of the Argentine Basin flow is of climatic relevance, as it yields strong mixing between Antarctic water masses (carried by the Malvinas Current) and subtropical water masses (carried by the Brazil Current). Such mixing is regulated by the Zapiola Anticyclone, a counterclockwise current that encircles the Zapiola Rise, the main topographic feature of the Argentine Basin. We investigate the intrinsic variability of the Argentine Basin flow by using a sigma-coordinate ocean model. The periodic domain of integration includes the Pacific/Atlantic sector of the Southern Ocean, which allows us to describe correctly the Antarctic Circumpolar Current and its fronts. The forcing is provided by steady climatological surface heat and momentum fluxes. Results show several phenomena of both high and low-frequency variability which are found to be sensitive to background stratification and the degree of smoothing of the bottom topography. The Argentine Basin circulation is found to be related to fluctuations of the position of the Antarctic Circumpolar Current fronts. Significant agreement is found when comparing our model results with altimeter data