Mixing in the Brazil-Malvinas confluence

Abstract

Conductivity-temperature-depth profile data from the Western Argentine Basin collected from 1984 to 1989 are used to quantify the cross-front heat and salt transfers associated with the vertical finestructure across the Brazil-Malvinas Confluence. The fluxes are estimated following the statistical model of Joyce ( Journal of Physical Oceanography, 7, 626–629, 1977). The data indicate that the upper ocean cross-front structure of the large-scale temperature and salinity fields is constant. The medium-scale finestructure intensity is quantified by the variance of the vertical temperature and salinity gradients in the 10–100 m wavelentgh band. Due to the abundance of intrusions, the upper layer (0–1000 m) variances increase by a factor of four at distances <20 km from the front. Heat and salt flux estimates associated with medium-scale mixing in the upper ocean are of the order 10 −2oC m s −1 and 10 −3 m s −1 respectively. These fluxes are an order of magnitude greater than availabe estimates for other frontal regions. The medium-scale finestructure may therefore play a key role in the dissipation of eddies and intrusive lenses in the region. Heat and salt fluxes between North Atlantic Deep Water and Circumpolar Deep Water are 6.5 × 10 −4 °C m s −1 and 1.8 × 10 −4 m s −1, and agree with existing estimates. Extrapolation of upper layer Brazil-Malvinas Confluence cross-frontal fluxes to the Subtropical Convergence across the South Atlantic suggests that the medium-scale southward heat flux is about 20% of the oceanic northward heat flux at 30°S. Similarly, the freshwater flux balances 20% of the excess evaporation north of 30°S.