A view of the Brazil-Malvinas confluence, March 2015

The encountering of the subtropical Brazil Current (BC) and the subantarctic Malvinas Current (MC) along the western margin of the Argentine Basin forms the Brazil-Malvinas Confluence (BMC), one of the most intense open-ocean fronts in the world ocean and a site for the formation of intermediate water masses. Here, we provide a comprehensive description of the BMC based on physical and biogeochemical data – hydrographic stations, profiling floats and subsurface drifters – gathered in March 2015. We use these data in order to characterize the impinging and outflowing currents and to describe the cross- and along-frontal thermohaline structure. In addition, we compare the in-situ measurements with both climatological data and the Mercator Ocean eddy-resolving reanalysis. The hydrographic sections illustrate the contrasting properties between the two western boundary currents: warm, salty, nutrient- and oxygen-poor oligotrophic subtropical waters carried southward by the BC and the cold, fresh, oxygen- and nutrient-rich subantarctic waters carried northward by the MC. The frontal system is also characterized by the presence of thermohaline intrusions, with the cross-frontal gradients and along-front velocities sharpening as the colliding currents shape the frontal system. We also observe brackish waters spreading on top of the frontal jet as a result of both the confluence dynamics and off-shelf advection favored by north-easterly winds. These low-salinity waters are positively correlated with surface ageostrophic speeds over the frontal jet. The cruise data illustrates the high regional and mesoscale variability as compared with climatological conditions, and further document the submesoscale subsurface complexity, which is not properly captured by available operational models.Fil: Orúe Echevarría, Dorleta. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Pelegrí, Josep L.. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Alonso González, Iván J.. Oceomic, Marine Bio And Technology S.L; EspañaFil: Benítez Barrios, Verónica M.. Oceomic, Marine Bio And Technology S.L; EspañaFil: Emelianov, Mikhail. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: García Olivares, Antonio. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Gasser i Rubinat, Marc. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: De La Fuente, Patricia. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Herrero, Carmen. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Isern Fontanet, Jordi. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Masdeu Navarro, Marta. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Peña Izquierdo, Jesús. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Piola, Alberto Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Ramírez Garrido, Sergio. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Rosell Fieschi, Miquel. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Salvador, Joaquín. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Barcelona; EspañaFil: Valla, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Vallès Casanova, Ignasi. Consejo Superior de Investigaciones Científicas. Instituto de Ciencias del Mar; EspañaFil: Vidal, Montserrat. Universidad de Barcelona; Españ

Imprint of Southern Ocean eddies on winds, clouds and rainfall

Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. The impact of these transitory and approximately circular sea surface temperature fronts on the overlying atmosphere is not well known. Stationary fronts such as the Gulf Stream have been reported to lead to pronounced atmospheric changes1, 2. However, the impact of transient ocean eddies on the atmosphere has not been determined systematically, except on winds and to some extent clouds3, 4, 5, 6. Here, we examine the atmospheric conditions associated with over 600,000 individual eddies in the Southern Ocean, using satellite data. We show that ocean eddies locally affect near-surface wind, cloud properties and rainfall. The observed pattern of atmospheric change is consistent with a mechanism in which sea surface temperature anomalies associated with the oceanic eddies modify turbulence in the atmospheric boundary layer. In the case of cyclonic eddies, this modification triggers a slackening of near-surface winds, a decline in cloud fraction and water content, and a reduction in rainfall. We conclude that transient mesoscale ocean structures can significantly affect much larger atmospheric low-pressure systems that swiftly pass by at the latitudes investigated