The Burdwood Bank Circulation

A suite of high-resolution numerical simulations characterizes the oceanic circulation in the Burdwood Bank, a shallow seamount located in the northeastern end of the Drake Passage. Model analysis shows energetic upwelling and mixing uplifting deep and benthic waters into the photic layer. Tides and the Antarctic Circumpolar Current are the primary drivers of the bank's circulation. Tidal forcing is the main driver for the entrainment of deep waters into the upper layers of the bank and local wind forcing for the detrainment of these waters into the deep ocean. Passive tracer diagnostics suggest that the dynamical processes triggered by the Burdwood Bank could have a significant impact on local ecosystems and the biogeochemical balance of the southwestern Atlantic region, which is one of the most fertile portions of the Southern Ocean. Model results are robust—they are reproduced in a wide array of model configurations—but there is insufficient observational evidence to corroborate them. Satellite color imagery does not show substantial chlorophyll blooms in this region but it shows strong phytoplankton plumes emanating from the bank. There are several potential explanations for the chlorophyll deficit, including lack of light due to persistent cloud cover, deep mixing layers, fast ocean currents, and the likelihood that blooms, while extant, might not develop on the surface. None of these possibilities can be confirmed at this stage.Fil: Matano, Ricardo P.. State University of Oregon; Estados UnidosFil: Palma, Elbio Daniel. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados Unido

A Numerical Study of the Magellan Plume

In this modeling study we investigate the dynamical mechanisms controlling the spreading of the Magellan Plume, which is a low-salinity tongue that extends along the Patagonian Shelf. Our results indicate that the overall characteristics of the plume (width, depth, spreading rate, etc.) are primarily influenced by tidal forcing, which manifests through tidal mixing and tidal residual currents. Tidal forcing produces a homogenization of the plume’s waters and an offshore displacement of its salinity front. The interaction between tidal and wind-forcing reinforces the downstream and upstream buoyancy transports of the plume. The influence of the Malvinas Current on the Magellan Plume is more dominant north of 50S, where it increases the along-shelf velocities and generates intrusions of saltier waters from the outer shelf, thus causing a reduction of the downstream buoyancy transport. Our experiments also indicate that the northern limit of the Magellan Plume is set by a high salinity discharge from the San Matias Gulf. Sensitivity experiments show that increments of the wind stress cause a decrease of the downstream buoyancy transport and an increase of the upstream buoyancy transport. Variations of the magnitude of the discharge produce substantial modifications in the downstream penetration of the plume and buoyancy transport. The Magellan discharge generates a northeastward current in the middle shelf, a recirculation gyre south of the inlet and a region of weak currents father north.Fil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Matano, Ricardo. Oregon State University; Estados Unido

An idealized study of near equatorial river plumes

The dynamics of near equatorial river plumes (NERPs) are investigated using a highly idealized model. The spreading of a NERP from an eastern boundary is characterized by a continuous shedding of westward propagating eddies. This process transfers the bulk of the freshwater discharge to the deep ocean, thus distinguishing NERPs from their midlatitude counterparts. In the long-term limit, a NERP can be rationalized as a β-plume emanating from a coastal source. The evolution of NERPs in an unstratified basin is quite different from that in a stratified one. The spin-up in an unstratified basin is characterized by the formation of an anticyclonic bulge, which spreads westward thus creating a density stratification that favors the subsequent development of smaller and faster moving secondary eddies. The collision of the secondary eddies with the leading bulge arrests the effects of mixing thus allowing the further spreading of the buoyancy anomaly. In a stratified basin, the generation of anticyclonic eddies is accompanied by a concurrent generation of cyclones, which pump saltier waters to the surface hence leading to smaller sea surface salinity (SSS) anomalies. NERPs are sensitive to variations of the freshwater flux (Qfw) and the geomorphological setting. Larger Qfw generates bigger eddies, which spread at a rate proportional to the square root of the normalized flux. Wide shelves allow the interaction of the eddies with the bottom, thus promoting a cyclonic shift of the axis of the eddy train. The inclination of the coast affects the dynamical balance controlling the near-field behavior of NERPs.Fil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Matano, Ricardo. State University of Oregon; Estados Unido

The influence of the Brazil and Malvinas Currents on the Southwestern Atlantic Shelf Circulation

The oceanic circulation over the southwestern Atlantic shelf is influenced by large tidal amplitudes, substantial freshwater discharges, high wind speeds and – most importantly – by its proximity to two of the largest western boundary currents of the world ocean: the Brazil and Malvinas currents. This review article aims to discriminate the dynamical processes controlling the interaction between this extensive shelf region and the deep-ocean. The discussion is focused on two broad regions: the South Brazil Bight to the north, and Patagonia to the south. The exchanges between the Brazil Current and the South Brazil Bight are characterized by the intermittent development of eddies and meanders of the Brazil Current at the shelfbreak. However, it is argued that this is not the only – nor the most important – influence of the Brazil Current on the shelf. Numerical simulations show that the thermohaline structure of the South Brazil Bight can be entirely ascribed to steady state, bottom boundary layer interactions between the shelf and the Brazil Current. The Malvinas Current does not show the development of eddies and meanders, but its influence on the Patagonian shelf is not less important. Models and observations indicate that the Malvinas Current not only controls the shelfbreak dynamics and cross-shelf exchanges but also influences the circulation in the shelf's interior.Fil: Matano, Ricardo. Oregon State University; Estados UnidosFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Centro Arg.de Oceanografía; Argentina. Universidad de Buenos Aires; Argentin

Características Físicas de Plumas Atrapadas por el Fondo

La descarga de estuarios y ríos sobre la plataforma continental forma plumas que transportan aguas menos salinas conjuntamente con sedimentos, nutrientes y materiales antropogénicos. Aunque se ha avanzado considerablemente en el conocimiento de la dinámica de plumas superficiales (confinadas a las capas superiores del océano), aquellas atrapadas por el fondo (que ocupan toda la columna de agua) han recibido mucha menos atención. Debido a que estas últimas son generadas por grandes descargas, su impacto en el ecosistema oceánico es mayor. Este trabajo se propone como objetivo ampliar estudios previos analizando la naturaleza de los procesos físicos básicos asociados a la penetración longitudinal y transversal y al transporte de flotabilidad de plumas de gran escala mediante el empleo de modelos oceánicos implementados en un dominio simplificado. En el mismo se analiza la sensibilidad de esas características ante variaciones ambientales (pendiente de la plataforma, fricción de fondo, difusión lateral). Las características de la pluma difieren fundamentalmente aguas abajo (D) y aguas arriba (U) de la descarga. El transporte de flotabilidad en la región D disminuye considerablemente con el aumento de pendiente, siendo compensado por un incremento correspondiente en la región U. Un incremento de la pendiente retrae la pluma hacia la costa en la región D, mientras que expande la pluma transversalmente a la costa en la zona U. La expansión lateral de la pluma en la superficie se halla controlada mayormente por la fricción de fondo. Los resultados muestran además una marcada dependencia del transporte de flotabilidad con la mezcla lateral para todas las pendientes, siendo mayor el transporte en la región D a medida que disminuye la mezcla.Fil: Sitz, Lina Elisabet. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Matano, Ricardo. State University of Oregon; Estados Unido

Dynamical analysis of the oceanic circulation in the Gulf of San Jorge, Argentina

This study identifies the dynamical mechanisms driving seasonal variations in oceanic circulation and water mass characteristics of the Gulf of San Jorge (GSJ) and its exchanges with the Patagonian Shelf (PS). A suite of process-oriented numerical experiments indicates that GSJ circulation is mainly driven by tidal forcing and modulated by wind forcing and intrusions from the PS. During late spring and summer, stratification decouples the upper and deeper layers of the gulf, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. The subsurface circulation is induced by differential tidal mixing in coastal and deep areas and its intensity is strongly affected by the temporal variability of the atmospheric heat flux, which increases from spring to summer and fades from fall to winter. As stratification weakens, circulation patterns are replaced by wind-driven anticyclonic gyres in the south and an open cyclonic loop in the north. Passive tracer diagnostics show that in summer, surface and subsurface waters from the GSJ northern coast are exported and replaced by waters from the coastal portion of PS currents. The renewal of bottom waters is slower: A small portion upwells in the southwestern coast but most are ventilated by winter convection in the southern region and by intrusions of PS waters in the northern region.Fil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Matano, Ricardo. State University of Oregon; Estados UnidosFil: Tonini, Mariano Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Martos, Patricia. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados Unido

Dinámica oceánica en la región del talud Patagónico

La región del talud de la Plataforma Continental Argentina es considerada una de las áreas de mayor productividad primaria del océano mundial. A diferencia de otras regiones de alta productividad caracterizadas por surgencia (upwelling) costera generada por el viento estacional, estudios recientes indican que en el caso de la plataforma y talud patagónico la surgencia estaría favorecida por la intrusión de nutrientes relacionados al flujo de la Corriente de Malvinas. Este trabajo se propone como objetivo ampliar estos estudios analizando la naturaleza de los procesos físicos básicos asociados al intercambio dinámico de propiedades entre la plataforma continental y el océano profundo mediante el empleo de modelos oceánicos simplificados. En el mismo se analiza la sensibilidad del mecanismo de intercambio ante variaciones ambientales (pendiente del talud, pendiente de la plataforma, fricción de fondo) y del forzante (intensidad y distribución transversal de la corriente incidente) con especial énfasis en la región Patagónica. Los resultados analíticos y numéricos sin variación longitudinal de la topografía muestran que la intensidad del intercambio a través del talud y la surgencia asociada aumenta con la intensidad de la corriente del talud, la pendiente del talud y el rozamiento del fondo. Variaciones en la forma del perfil de velocidades en el talud y del transporte de la corriente indican que la surgencia aumenta con el aumento del transporte, siendo la magnitud del flujo incidente en el borde de talud (punto de quiebre entre la pendiente de plataforma y talud) la variable con mayor incidencia en la intensidad de la surgencia. Por otro lado, la presencia de una corriente de plataforma en la misma dirección que la corriente de talud contrarresta la surgencia, pudiendo llegar, en algunos casos, a invertir el movimiento vertical en el borde de talud.Fil: Ascuaga, María Eugenia. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Matano, Ricardo. State University of Oregon; Estados Unido

The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations

Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35°S. Away from the tropics, these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-defined seasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelf waters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36°S to 37°30′S). In contrast, in fall and winter, low-salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters in the open ocean.Fil: Guerrero, Raul Alfredo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografia Naval; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Fenco, Harold. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Matano, Ricardo. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Combes, Vincent. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Chao, Yi. University of California at Los Angeles; Estados Unidos. Remote Sensing Solutions Inc.; Estados UnidosFil: James, Corinne. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Strub, P. Ted. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados Unido

The Salinity Signature of the Cross-Shelf Exchanges in the Southwestern Atlantic Ocean: Numerical Simulations

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the inter- annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.Fil: Matano, Ricardo. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Combes, Vincent. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografia Naval; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; ArgentinaFil: Guerrero, Raul Alfredo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Strub, P. Ted. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: James, Corinne. Oregon State University. College of Earth, Ocean and Atmospheric Sciences; Estados UnidosFil: Fenco, Harold. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Chao, Yi. Remote Sensing Solutions; Estados UnidosFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentin

Dramatic Rise in Plasma Viremia after CD8+ T Cell Depletion in Simian Immunodeficiency Virus–infected Macaques

To determine the role of CD8+ T cells in controlling simian immunodeficiency virus (SIV) replication in vivo, we examined the effect of depleting this cell population using an anti-CD8 monoclonal antibody, OKT8F. There was on average a 99.9% reduction of CD8 cells in peripheral blood in six infected Macaca mulatta treated with OKT8F. The apparent CD8 depletion started 1 h after antibody administration, and low CD8 levels were maintained until day 8. An increase in plasma viremia of one to three orders of magnitude was observed in five of the six macaques. The injection of a control antibody to an infected macaque did not induce a sustained viral load increase, nor did it significantly reduce the number of CD8+ T cells. These results demonstrate that CD8 cells play a crucial role in suppressing SIV replication in vivo