Projected Change of The Southwest Atlantic Circulation

The circulation of the southwestern Atlantic region is characterized by the confluence of the poleward Brazil Current and the equatorward Malvinas Current flowing along the shelfbreak. Located near 38°S, the highly energetic Brazil/Malvinas Confluence is determined by the dynamical balance between the opposing transports of the Brazil and Malvinas Current and is the main pathway of the shelf waters to the open ocean. The goal of this study is to assess how the Southwest Atlantic circulation and shelf/open ocean water exchanges are projected to change under greenhouse gas increases. To do so, we have downscaled several ocean models from the Coupled Model Intercomparison Project (CMIP5) found to unrealistic represent the shelf circulation. The model experiments indicate that the latitude of the Confluence consistently shifts to higher latitudes under a global warming scenario. We surmise that it results from an intensification of the Brazil Current (due to a strengthening of the subtropical gyre) and from a weakening of the Malvinas Current (due to southward shift of the Antarctic Circumpolar Current jets). Over the shelf, the projected transport seems to be comparable to the one of present day of Argentina but stronger off Brazil. We therefore expect that the transport of total nutrient-rich shelf water to the open ocean will be stronger and located further south, which thus might lead to changes in today’s ecosystem.