Continental Shelf Waters in the Brazil-Malvinas Confluence

FREITAS, A. C.; BIANCHI, A. A.; PALMA, E. D.

Foz do Iguacu

Congreso; 2010 Meeting of the Americas; 2010

American Geophysical Union

The dynamics of the oceanic region between Southern Brazil andNorthern Argentina is highly influenced by the collision near 38oS ofthe Brazil and Malvinas Currents (the Brazil-Malvinas Confluence,BMC). This area has a complex circulation with eddies, rings, andfilaments in the upper layer and a high productivity due to nutrientenrichment from Subantarctic waters and continental sources carriedby the large freshwater discharge of the La Plata river. Although asignificant number of studies were carried on the BMC area, few ofthem address the dynamics of mixing and shelf-deep ocean exchangeof the low salinity waters. An advance in this area is important bothfor climate and biological studies. In this study, historicalhydrographic data from BMC and numerical simulations are used toexamine the thermohaline water properties and to calculate thegeostrophic transport of the low salinity layer (S <33.8). Thenumerical model (Princeton Ocean Model - POM) was initialized withclimatological annual mean temperature and salinity and forced withoutputs from global models, hydrographic databases and assimilationfrom satellite data. The historical hydrographic sections show shelfwater occurrence in the Brazil-Malvinas Confluence. In some cases, alow salinity layer with thickness of approximately 100 m and width of100 km is observed along the Confluence. The geostrophic velocityand volume transport estimates of the low salinity filaments are ~1m/s and 1.4 Sv (1Sv =106 m3/s), respectively. The presence of the lowsalinity layer in the BMC suggests that there is a net transference ofshelf water to the open ocean. However, the data do not show aseasonal pattern. The model simulations also show yearlongintrusions ("pulses") of shelf water in the slope region. Given that thePatagonian Shelf sequestrates a large amount of CO2 (~ 4mmol m-2day-1) from the atmosphere the above results indicates that the BMCjet can be the main conduit by which the excess CO2 is diverted todeeper areas of the Southwestern Atlantic.