Academic literature on the topic 'Malvinas Current'

Abstract The confluence of the Brazil–Malvinas Currents maintains strong sea surface temperature (SST) fronts in the midlatitude southwestern Atlantic year-round. SST effects on near-surface stability and surface wind variations are examined in this region using satellite and in situ datasets. Satellite observations show strong (weak) surface wind speeds over the warm Brazil (cold Malvinas) Current. A novel feature of this study is the construction of a high-resolution surface meteorological dataset that is based on historical ship observations. Analysis of this new in situ dataset reveals an increased (reduced) sea–air temperature difference over the Brazil (Malvinas) Current, indicating destabilization (stabilization) in the atmospheric boundary layer. These results are consistent with the SST-induced vertical mixing mechanism for wind adjustment. The SST effect on the near-surface atmosphere is observed both in the climatology and on interannual time scales in the Brazil–Malvinas confluence. Along a zonal SST front at 49°S northeast of the Malvinas/Falkland Islands, there is a collocated line of surface wind divergence, with moderate convergence to the north. Vertical mixing does not explain this divergence pattern because the prevailing surface winds are westerly, blowing in parallel with the front. An additional mechanism is proposed for boundary layer wind adjustment.

Abstract. 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.

Abstract. 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 describe the dynamical processes controlling the interaction between the shelf 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 no less important. Models and observations indicate that the Malvinas Current not only controls the shelfbreak dynamics and cross-shelf exchanges but also the circulation in the shelf's interior.

The latest studies on the tectonic evolution of the Malvinas (Falkland) Islands and their adjacent continental plateau further east are analyzed to assess a long controversy regarding the origin of these islands. Although there has been a controversy for several decades on this subject, new technologies and exploratory drilling have brought new data, however the debate of the geological evolution of this area remains open. The two dominant hypotheses are analyzed by assessing the eventual collision between the islands and the South American continent, the presence of a large transcontinental fault such as Gastre, the potential 180º rotation of the Malvinas Islands, and the occurrence of a mega-decollement with opposite vergence. These hypotheses are contrasted with the processes that have occurred in Patagonia, especially those based on the new isotopic data on the Maurice Ewing Bank at the eastern end of the Malvinas Plateau, and the current knowledge of the adjacent Malvinas Basin. The new data highlights the inconsistencies of certain models that proposed these islands migrated from the eastern African coasts near Natal, to their current position and rotated 180º on a vertical axis. The new observations are consolidating the hypothesis that postulates that the islands have been part of the South American continent since before the Paleozoic.

O objetivo deste trabalho foi analisar a influência dos gradientes de TSM e da passagem de sistemas atmosféricos transientes sobre a região da Confluência Brasil-Malvinas (CBM) no Oceano Atlântico Sudoeste e descrever a variabilidade espacial e temporal da concentração de vapor d’água dentro da camada limite atmosférica marinha (CLAM). Os dados foram obtidos a partir de 130 perfis de radiossondas realizados durante dez cruzeiros oceanográficos feitos durante os meses de outubro e novembro entre 2004 e 2015. Os resultados mostram que os gradientes termais entre as águas quentes da Corrente do Brasil e as águas frias da Corrente das Malvinas foram capazes de produzir diferenças significativas no conteúdo de vapor d'água na CLAM nos dois lados da frente oceanográfica. Na superfície, o valor médio da umidade específica sobre o lado quente (frio) foi 8,4 ± 1,67 mm (7,08 ± 1,51 mm). Em todas as observações realizadas, a umidade integrada na CLAM foi diretamente influenciada pela advecção e pela passagem de sistemas atmosféricos transientes. A B S T R A C TThe objective of this work was to analyze the influence of the SST gradients and the passage of transient atmospheric systems at the Brazil-Malvinas Confluence (BMC) region in the Southwest Atlantic Ocean, and to describe the spatial and temporal variability of the water vapor concentration within the marine atmospheric boundary layer (MABL). The data were obtained from 130 radiosondes profiles taken during ten oceanographic cruises carried out during the months of October and November between 2004 and 2015. The results show that the thermal gradients between the warm waters of Brazil Current and the cold waters of the Malvinas Current were able to produce significant differences in the water vapor content of the MABL on both sides of the oceanographic front. On the surface, the average of the specific humidity over the warm (cold) side was 8.4 ± 1.67 mm (7.08 ± 1.51 mm). In all the observations made, the water vapor integrated in the MABL was directly influenced by the advection and by the passage of transient atmospheric systems. Key words: Water Vapor; Brazil-Malvinas Confluence; Atmospheric boundary layer

Abstract. The Patagonia continental shelf located off southeastern South America is bounded offshore by the Malvinas Current, which extends northward from northern Drake Passage (~55° S) to nearly 38° S. The transition between relatively warm-fresh shelf waters and Subantarctic Waters from the western boundary current is characterized by a thermohaline front extending nearly 2500 km. We use satellite derived sea surface temperature, and chlorophyll-a data combined with hydrographic and surface drifter data to document the intrusions of slope waters onto the continental shelf near 41° S. These intrusions create vertically coherent localized negative temperature and positive salinity anomalies extending onshore about 150 km from the shelf break. The region is associated with a center of action of the first mode of non-seasonal sea surface temperature variability and also relatively high chlorophyll-a variability, suggesting that the intrusions are important in promoting the local development of phytoplankton. The generation of slope water penetrations at this location may be triggered by the inshore excursion of the 100 m isobath, which appears to steer the Malvinas Current waters over the outer shelf.

Bien que le Courant des Malouines (CM) soit le principal soutien de la productivité élevée qui caractérise l’Atlantique Sud-Ouest il reste encore peu documenté. Cette thèse combine des données in situ et satellitaires et des sorties de modèles opérationnels, pour étudier le CM. Le CM est une émanation du courant Antarctique Circumpolaire (ACC). Il s’écoule vers le nord jusqu’à 38°S puis il retourne vers le sud formant le Courant de Retour des Malouines (CRM). Nous montrons que l’énergie turbulente de l’ACC est filtrée sur le plateau des Malouines (55°S-48°S). Nous avons découvert l'occurrence d’évènements de blocage à 48S qui coupent le CM de sa source l’ACC. Le CM devient alors le bord ouest d’une grande cellule de recirculation cyclonique. Nous avons montré que les positions des fronts du système du CM (Front Polaire, Front Subantarctique et Front du Brésil) peuvent être suivies en définissant des critères sur la densité potentielle et la hauteur de l’eau. Des eaux du sud du front polaire (FP) sont injectées dans le CM (évènements d'alimentation) et recirculent entre le CM et le CRM. Les caractéristiques des eaux de la recirculation varient dans le temps en fonction des évènements d’alimentation et de blocage. Une série temporelle de 24 ans du transport du CM à 41°S a été construite à partir de données de mouillages et d’altimétrie satellitale. Les maxima et minima du transport sont liés à des perturbations de la circulation en provenance du Bassin Argentin (et non de l’ACC): les maxima sont dus à des tourbillons détachés du FP et les minima à des anomalies anticycloniques provenant du courant de Brésil
Although the Malvinas Current (MC) plays a key role over the Patagonian shelf in sustaining an extremely rich ecosystem it remains rather undocumented. In this thesis, we combined in situ, satellite data, and operational model outputs to study the MC. The MC is an offshoot of the Antarctic Circumpolar Current (ACC). It flows northward up to 38°S where it turns southward forming the Malvinas Return Flow (MRF). We show that a substantial portion of the mesoscale activity from the ACC is dissipated over the Malvinas Plateau. We discovered the occurrence of recurrent blocking events cutting the MC from its source, the ACC. However, the MC does not collapse as a recirculation cell is established. Criteria in potential density and dynamic topography were defined to study the MC system fronts (Polar Front, Subantarctic Front and Brazil Current Front). Waters from the South of the Polar Front (PF) are recurrently injected into the MC as pulses or feeding events. Polar waters accumulate in the recirculation region between the MC and the MRF. Variations in the water characteristics of the recirculation region are consistent with changes in the occurrence of blocking and feeding events. Combining mooring and satellite altimetric data, a 24-year long time series of the MC transport at 41 ° S was constructed. Maxima and minima of the Malvinas current transport at 41 ° S are not associated with the ACC, rather with eddies coming from the Argentine Basin. Transport maxima appear to be related with cyclonic eddied detached from the Polar Front and transport minima with large anticyclonic anomalies from the Brazil Current

O papel do Oceano Atlântico Sul na manutenção do clima global é de extrema importância uma vez que compõe uma das partes fundamentais da circulação Termohalina Global. Nesse contexto, o Sudoeste do Atlântico Sul é uma região complexa e energética, onde duas correntes de contorno oeste de sentidos opostos se encontram formando a Confluência Brasil-Malvinas. O objetivo deste trabalho é investigar mudanças de longo período na variabilidade da latitude de separação da Corrente do Brasil (CB) da Plataforma Continental, considerada um delimitador do limite sul do Giro Subtropical do Atlântico Sul na região do Sudoeste do Atlântico Sul. Para tal, foi usado resultados do modelo HYCOM em um experimento datado denominado ATIa0,25. O modelo foi forçado por dados da reanálise do NCEP e seus resultados abrangem o período de 1960 a 2010. A latitude de separação da CB da costa foi definida neste trabalho como o ponto em que a isoterma de 18°C cruza a isóbata de 1000 metros de profundidade. A variabilidade da latitude de separação da CB pode ser dividida em três momentos principais: no começo a latitude de separação está ao sul de sua média, na década de 70 está a norte de sua posição média até a década de 90; depois dos anos 90 a posição começa a se deslocar para sul até 2010. As tendências encontradas são 0,37 ± 0,02°/década entre 1960 e o final da década de 70 e 0,10 ± 0,01°/década de 1980 a 2010. Os transportes das correntes do Brasil e das Malvinas, as latitudes dos rotacionais nulo e máximo do vento e o índice do Modo Anular Sul são também analisados no período de 1960 a 2010, como possíveis forçantes da variação da latitude da separação da CB. Todas a séries obtidas apresentam mudança ao intensificação das tendências entre as décadas de 70 e 80 - assim como na série de separação da CB. Esse comportamento pode estar relacionado ao Modo Anular Sul. Este modo de variabilidade climática afeta as forçantes de separação da CB em escalas de tempo diferentes. O deslocamento para sul do limite sul do Giro Subtropical do Atlântico Sul observado nesse trabalho inicia-se no início da década de 90 e está relacionado com mudanças nos regimes de vento da bacia causadas provavelmente por mudanças nos campos de temperatura de superfície do mar.
The role of South Atlantic Ocean on global climate is highly important since it compounds one of the most significant parts of Thermohaline Circulation, the Atlantic Meridional Overturning Circulation. In this sense, the Southwestern South Atlantic is a complex and energetic region, where two western boundary currents, coming in opposite directions, encounter each other forming the Brazil-Malvinas Confluence. The goal of this work is to investigate long-term changes in the latitude of separation of the Brazil Current, considered as the southern limit of the South Atlantic Subtropical Gyre in the Southwestern South Atlantic. In this investigation, results of a numerical experiment with the model HYCOM, dubbed ATIa0.25, were used. The model was forced with NCEP reanalysis products and its results cover the period of 1960 to 2010. The Brazil Current separation latitude was defined as the point where the 18°C isotherm crosses the 1000 meters depth isobath. The variability of the CB separation latitude can be divided in three periods: at the beginning of experiment, the separation point has a tendency to move southward of it\'s mean position; From the 70\'s to the 90\'s, it shows a northward tendency; after the 90\'s it started again a southward shift until 2010. The trends of the northward shifts are of 0.37 ± 0.02°/decade in the 70\'s and 0.10 ± 0.01°/decade between 80\'s and 2010\'s. Brazil and Malvinas currents transports, the latitude of zero and maximum value of the wind stress curl and the Southern Annular Mode index are also analyzed for the 1960-2010, period as possible forcing mechanisms of BC separation latitude. All series obtained presents changes or intensification on trends between 70\'s and 80\'s decades - so do the series of BC separation latitude. This behavior can be related to the Southern Annular Mode. This climatic mode of variability affects the forcing mechanisms of the BC separation latitude in different time scales. The southward shift of the southern limit of South Atlantic Subtropical Gyre observed in this work starts in the beginning of 90\'s decade and is related with changes in wind patterns, probably due to changes in sea surface temperature distribution.

A variação do nível do mar em relação ao geóide é conhecida como Topografia Dinâmica do oceano, cuja determinação é importante no estudo da circulação geostrófica, vórtices e outros fenômenos. O sinal do geóide predomina na definição da topografia dinâmica em todos os comprimentos de onda, ou seja, o nível do mar está intimamente ligado ao campo geopotencial. Os modelos geoidais globais anteriores ao GRACE eram precisos para comprimentos de onda com centenas de quilômetros, já em curtos comprimentos de onda (menores que 100 km) esses modelos não possuíam resolução suficiente, prejudicando assim a determinação da TD e, conseqüentemente, o estudo de fenômenos com comprimentos de ondas na faixa de 100 a 200 km. No desenvolvimento do modelo EGM96, foram inseridos novos dados gravimétricos de superfície, além de dados de órbitas de satélites e altimetria, obtendo-se assim melhora considerável em relação ao modelo OSO91A (incorporado aos dados do TOPEX/Poseidon); ainda sim, o modelo EGM96 possui erro de aproximadamente 18 cm, que é considerado alto para várias aplicações oceanográficas. Recentemente, foram divulgados os modelos globais do campo de gravidade EIGEN-5C (obtido através dos dados do GRACE) e EGM2008, completos para grau e ordem 360 e 2159 em termos de coeficientes harmônicos esféricos, respectivamente; estes modelos possibilitaram a estimativa de correntes com resolução e precisão superior ao modelo EGM96. No presente trabalho, os modelos geoidais citados acima, juntamente com o modelo de nível médio do mar DNSC08, foram usados na determinação da topografia dinâmica média e das correntes geostróficas absolutas médias (no período de 2003 a 2008) utilizando o método de filtragem SSA no Atlântico Sul (20o N a 55o S, 80o W a 20o E) . Os resultados foram comparados com produtos do modelo numérico HYCOM, demonstrando que os modelos geoidais recentes (EIGEN-5C e EGM2008) apresentaram resultados satisfatórios na determinação da TDM e correntes, com a plena identificação das principais feições de grande e meso escala, o que não ocorre com a TDM do EGM96. A Corrente do Brasil, entre 20°S e 30°S, na isóbata de 200 m, apresentou velocidades resultantes médias de aproximadamente 0.20 m/s (desvio padrão de 0.09 m/s) quando determinada com a TDM-EGM2008, 0.22 m/s (desvio padrão de 0.12 m/s) vii utilizando a TDM-EIGEN-5C, embora os ruídos interfiram na estimativa, e 0.30 m/s (desvio padrão de 0.17 m/s) considerando a TDM-EGM96; o modelo numérico HYCOM forneceu velocidade de 0.25 m/s (desvio padrão de 0.13 m/s) na mesma região. Estatisticamente, as correntes do modelo TDM-EGM08 possuem maior correlação espacial com o modelo numérico HYCOM, 0.7 para u (componente EW) e 0.69 para v (componente NS); por outro lado, as correntes oriundas da TDM-EIGEN-5C apresentaram uma correlação de 0.62 para u e 0.64 para v, enquanto que as correntes do modelo TDM-EGM96 apresentaram uma correlação de 0.10 para u e 0.11 para v. Uma alternativa no uso de dados de altimetria de satélites (Jason, por exemplo) se encontra em dados de altimetria multi-satélites combinados com resultados de medições in-situ, submetidos a análise objetiva (são portanto dados combinados, MERGED, fornecidos pela AVISO); com esses dados se tem significativo aumento de precisão e resolução dos dados de altimetria, da topografia dinâmica e das correntes geostróficas. Na região que engloba a Confluência Brasil Malvinas (50o S a 20o S , 70 o W a 30o W) foram analisadas as variações temporais da topografia dinâmica e correntes oriundas de altimetria e do modelo geoidal EGM2008. Na análise específica desta região, verificouse que, apesar das principais feições terem sido identificadas, os dados de altimetria ainda carecem de resolução necessária no estudo das mesmas. O modelo EGM2008 apresentou os melhores resultados que os outros modelos (comparando com o modelo HYCOM e dados combinados de AVISO), devido à sua resolução espacial.
The variations of sea level relative to the geoid are known as Dynamic Ocean Topography (DOT), whose determination is important in studies of the geostrophic circulation, eddies and other phenomena. The sign of the geoid predominates in the definition of dynamic topography at all wavelengths, ie, sea level is closely linked to the geopotential field. Global geoid models prior to GRACE were precise for wavelengths of hundreds of kilometers, but in short wavelengths (less than 100 km) these models did not have enough resolution, thus impairing the determination of DOT and therefore the study of phenomena with wavelengths in the range of 100-200 km. In developing the EGM96, new surface gravity data were incorporated into the modeling, from satellite orbits and altimetry, resulting in a considerable improvement over the previous OSO91A (incorporated to TOPEX / Poseidon data); still EGM96 had a standard deviation of about 18 cm, considered too high for many oceanographic applications. Recently, global models of the gravity field were published, EIGEN-5C (obtained from GRACE data) and EGM2008, complete to degree and order 360 and 2159 in terms of spherical harmonic coefficients, respectively; these models allowed the estimation of currents with resolution and accuracy better than model EGM96. In this work, the geoid models mentioned above, along with models of mean sea level such as DNSC08, were used in the determination of DOT and absolute geostrophic currents (in 2003-2008) using the filtering method SSA (Singular Spectrum Analysis) in South Atlantic (20o N - 55o S , 80 o W - 20o E) . The results were compared with products from HYCOM hydrodynamic numerical model and show that recent geoid models (EIGEN-5C and EGM2008) lead to satisfactory results in determining the Average Dynamic Topography (ADT) and currents, with full identification of the main features of large and meso scales, which does not occur with ADT_EGM96. The Brazil Current (20°S-30°S), in the 200 m isobath, had average speed results of approximately 0.20 m/s (standard deviation 0.09 m/s) when computed with ADT-EGM2008, 0.22 m/s (standard deviation 0.12 m/s) by using ADT_EIGEN-5C, despite noise interference with the estimate, and 0.30 m/s (standard deviation 0.17 m/s) considering the ADT_EGM96; the numerical model HYCOM provided speed of 0.25 m/s (standard deviation 0.13 m/s) in the same region. Statistically, the currents based on model ADT_EGM08 have higher correlation with the numerical model HYCOM, 0.70 for u (EW component) and 0.69 for v (NS component); on the other hand, the currents computed with ADT_EIGEN-5C had correlations of 0.62 for u and 0.64 for v, while currents estimated from ADT_EGM96 showed correlations of 0.10 for u and 0.11 for v. An alternative in the use altimetry data (Jason, for example) is found in altimetry multi-satellites data combined with results of measurements in-situ, submitted to objective analysis; with these data, a significant increase of precision and resolution is reached for the altimetry data, dynamic topography and geostrophyc currents. In the region encompassing the Brazil Malvinas Confluence (50o S - 20o S , 70 o W - 30o W) were analyzed temporal variations of DOT and currents derived from altimetry and geoid model EGM2008. In the specific analysis of this region, it was found that although the main features have been identified, the altimetry data still lacks resolution to study them.The model EGM2008 showed the best results (comparing with the HYCOM model and combined data of AVISO), due to their spatial resolutions.