Argentine Basin

Altimeter observations analyzed by Fu et al. (2001) shows a very pronounced mode of variability in the Argentine Basin: a dipole in sea-surface height appears to rotate around a seamount -called Zapiola Rise- every 25 days. Bottom pressure measurements by Hughes et al. (2007) confirm the presence of strong barotropic oscillations, but at a period of only 19.6 days.

Argentine Basin mode

In Weijer et al. (2007a) we show that this discrepancy can be explained by the presence of multiple oscillatory modes. Two statistical techniques (POP and CEOF analysis), applied to 10 years of altimeter data, show several distinct statistical modes; one matches the Fu et al. (2001) observations, another those of Hughes et al. (2007). As a matter of fact, we identified a whole spectrum of modes in a shallow-water model of the Argentine Basin. The dominant mode with a period of 19.6 days clearly corresponds to the Hughes et al. (2007) oscillation. However, the mode displaying the clearest similarities (in spatial structure) with the Fu et al. (2001) observations shows up with a period of 31.5 days.

Argentine Basin mode

In Weijer et al. (2007b) we used a continuation method to link the spectrum of modes of the Argentine Basin to the Rossby basin modes in the flat, rectangular basin of classical theory. To this end, we defined a gradual transformation that morphed the full-bathymetry domain into a rectangular basin; and although in reality the modes are strongly controlled by bathymetry, (almost) each of them could be linked to a distinct classical Rossby basin mode.

Currently we are studying the sediment transport in the Argentine Basin to understand the controls on the existence and growth Zapiola Rise. In Weijer et al. 2015 we used passive tracers in an eddy-resolving ocean model to study whether sediment transport by the strongly turbulent circulation in the Argentine Basin can account for enhanced deposition over the Zapiola Rise. However, we found that the Zapiola Anticyclone is a barrier for sediment transport, leaving the Zapiola Rise as a sediment-starved region. Other processes, like resuspension, are probably critical to resolve this mystery.

References