Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, salinity. Acoustic impulses generated by an array of airguns suspended behind a vessel are reflected from these contrasts and recorded on long cables of hydrophones that are towed below the sea-surface. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of \textit{O}(10)~m. Here, I describe, process, and analyse a calibrated two-dimensional seismic survey from the Bellingshausen Sea of the Southern Ocean and a three-dimensional seismic survey from the Brazil-Falkland Confluence located offshore Uruguay. First, the Bellingshausen survey was designed to image the thermohaline structure across the west Antarctic shelf where warm-core eddies are reported. Processed and calibrated seismic images reveal the detailed thermohaline structure of Circumpolar Deep Water. Many warm-core eddies are observed, which have diameters of 1--12~km and thicknesses of 100--200~m. Pre-stack analysis demonstrates that this eddy field is being advected onto the shelf at speeds of \textit{O}(0.1)~m~s$^{-1}$. An iterative inverse modelling procedure is used to convert reflectivity into temperature and salinity, which confirms that the eddies have anomalously warm centres (i.e. $\sim$1$^{\circ}$C). These results have significant implications for ice shelf melting. Secondly, the Uruguay survey is used to investigate a large-scale frontal system. Although this system has been studied using hydrographic methods, these studies either have limited spatial resolution or have restricted depth penetration. The three-dimensional seismic survey, which was acquired in a `racetrack' pattern, permits the volume to be interrogated. Since the frontal system migrates southwestwards at a speed of \textit{O}(10)~km~day$^{-1}$, this survey is time-lapse in nature. Processed images reveal a band of dipping reflections that extend to depths of $\sim$2000~m. These reflections represent the frontal interface between the Brazil and Falkland currents. Physical oceanographic properties are calculated for images that cross this front. On the warm side of the front, the water mass is characterised by flat and continuous reflectivity. On the cold side of the front, the water mass is characterised by deformed reflectivity on all scales. Pre-stack analysis suggests that near-surface flow at the frontal interface is convergent. Between 0.5 and 1~km depth, a substantial eddy that is 30~km long and 250~m thick is visible on the cold side of the front. Detailed mapping suggests that this eddy grew and decayed over a period of 6~days. Its observed scale and duration are inconsistent with analytical and numerical studies of intra-thermocline eddies. Nevertheless, its duration is consistent with scaling arguments of frictional spin-down. Spatial and temporal distributions of mixing rates (i.e. diapycnal diffusivities) are estimated by spectrally analysing vertical displacements of automatically tracked reflections. Both internal wave and turbulent regimes are identifiable. Recovered diapycnal diffusivities are of \textit{O}($10^{-6}$--$10^{-2.2}$)~m$^{2}$~s$^{-1}$, consistent with hydrographically determined estimates. Mixing is suppressed and enhanced on the warm and cold sides of the front, respectively. Seismic Oceanography has considerable potential to quantify aspects of thermohaline circulation on multiple scales.

The objective of this study was to determine if fronts sustained up to three days will result in an aggregation of kingfish due to the anticipated accumulation of forage, increasing fishing success at these locations. Automated algorithms to detect frontal features in satellite-derived sea surface temperature, chlorophyll concentration, water clarity, and fluorescence images were successfully adapted for the coastal waters off west-central Florida. The surface ocean fronts were used to study the linkages between environmental conditions and recreational catch statistics of king mackerel (Scomberomorus cavalla) during 19 seasonal tournaments held in April to May and October to November of 2004 and 2005. The local winds estimated from a USF Coastal Ocean Monitoring and Prediction System observing station were analyzed with the frontal data to examine factors that influence oceanic frontal formation and stability. The front detection algorithms were also applied to high-r esolution bathymetry data which serves as a new technique for analyzing bottom topography. The spatial relationships between catch data collected through 415 angler interviews, frontal boundaries and stability, bathymetric gradients, bottom structure, and baitfish presence were identified using ESRI ArcGIS.Fishing success and fishing effort were highly variable regarding the distance of fishing activity to the nearest front. This was attributed to non-persistent winds. Intermediate water clarity (0.7 to 1.0 mW cm-2 microm-1 sr-1), the presence of baitfish, and the side of the front with relatively less chlorophyll showed the greatest influence on the king mackerel catch rates. Fishing success was found to be significantly higher at fishing locations where baitfish were reported present compared to where they were not reported. Concurrent with the 2005 harmful algal bloom event, a significant decrease in king mackerel catch occurred in the fall of 2005 (208 fish) compared to fall 20 04 (818) and spring 2005 (538). Additionally, fishing locations with baitfish present were observed about 15% less often during the fall of 2005 than the preceding seasons. From this, a model can be developed to diagnose the environmental conditions that can be used by resource managers to better understand variations in catch, which result from naturally occurring phenomena or man-induced overfishing.

Os padrões de circulação do Atlântico Sudoeste são caracterizados por uma diversidade de massas de água. A presença das correntes associadas ao giro subtropical e a incursão para norte da Corrente Circumpolar Antártica (CCA) determinam extensas regiões de largo gradiente de Temperatura da Superfície do Mar (TSM). Ao mesmo tempo, circulações de mesoescala geram intensos gradientes setorizados, ou reforçam o contraste de larga-escala. Consequentemente, frentes oceânicas de diferentes escalas são formadas ao longo desses gradientes. Quando o vento sopra sobre essas frentes, os fluidos trocam calor e momentum alterando suas propriedades dinâmicas e termodinâmicas. Nesse trabalho visamos caracterizar as alterações no campo de vento superficial que podem ser atribuídas a essas trocas. Para isso, foi aplicado um algoritmo de detecção de frentes em campos de Temperatura da Superfície do Mar (TSM) derivados do conjunto OSTIA. Em situações de escoamento atmosférico sinótico homogêneo, foram calculados o divergente e rotacional do vento medido pelo escaterômetro QuickSCAT ao longo das zonas frontais, bem como suas componentes perpendicular e paralela às frentes. Ao longo de 8 anos mais 96.000 frentes oceânicas foram detectadas, co-localizadas com a disponibilidade de dados de vento dando origem a 40.000 composições. O sistema de coordenadas dessas composições foi rotacionado para que as frentes oceânicas tivessem a mesma orientação. Nós empilhamos as composições em um arranjo 3D e foram obtidas médias das circulações atmosféricas induzidas. As perturbações médias obtidas indicaram que há convergência do vento quando este sopra do lado quente para o lado frio da frente com a frenagem do escoamento. De forma oposta, há divergência e aceleração do vento quando este sopra no sentido oposto. Nós identificamos alterações locais no rotacional do campo de vento capazes de induzir o bombeamento de Ekman no oceano. Esse processo pode gerar mecanismos de retroalimentação no sistema. Nossos resultados corroboram o de diversos estudos sobre o tema presentes literatura. / The southwest Atlantic circulation patterns are characterized by a diversity of water masses. The presence of currents associated with the subtropical gyre and the northward incursion of Antarctic Circumpolar Current (ACC) determine extensive regions of strong sea surface temperature gradient (SST). At the same time, mesoscale circulations generate intense local gradients, or reinforce the large-scale contrast. Consequently, oceanic fronts are formed along these gradients on different scales. When the wind blows over these fronts, the fluids exchange heat and momentum, and that changes their dynamic and thermodynamic properties. In this work we aim to characterize the changes in the surface wind field that might be attributed to these exchanges. To do it, a frontal detection algorithm was applied to the SST field derived from OSTIA set. We selected situations of synoptic homogeneous atmospheric flow and calculated the divergent and rotational wind, in addition to its perpendicular and parallel components to the oceanic fronts. We used wind measurements recorded by the QuickSCAT scatterometer along the frontal zones. More than 96,000 oceanic fronts were detected along 8 years of data. We matched them to available wind data and formed more than 40,000 SST-WIND compositions. The coordinate system of these compositions was rotated so that all oceanic fronts have the same horizontal orientation. We piled up the compositions in a 3D array and the temporal mean of the induced circulations was calculated. The average disturbance obtained indicated that there is wind convergence when it blows from the warm side of the front to the cold side because the flow is slowed down. Conversely, there is wind divergence when it blows in the opposite direction due to speeding up flow. We identified local changes in wind field curl capable of inducing Ekman pumping over the ocean. This process can generate feedback mechanisms in the system. Our results were consistent with the literature.

Os padrões de circulação do Atlântico Sudoeste são caracterizados por uma diversidade de massas de água. A presença das correntes associadas ao giro subtropical e a incursão para norte da Corrente Circumpolar Antártica (CCA) determinam extensas regiões de largo gradiente de Temperatura da Superfície do Mar (TSM). Ao mesmo tempo, circulações de mesoescala geram intensos gradientes setorizados, ou reforçam o contraste de larga-escala. Consequentemente, frentes oceânicas de diferentes escalas são formadas ao longo desses gradientes. Quando o vento sopra sobre essas frentes, os fluidos trocam calor e momentum alterando suas propriedades dinâmicas e termodinâmicas. Nesse trabalho visamos caracterizar as alterações no campo de vento superficial que podem ser atribuídas a essas trocas. Para isso, foi aplicado um algoritmo de detecção de frentes em campos de Temperatura da Superfície do Mar (TSM) derivados do conjunto OSTIA. Em situações de escoamento atmosférico sinótico homogêneo, foram calculados o divergente e rotacional do vento medido pelo escaterômetro QuickSCAT ao longo das zonas frontais, bem como suas componentes perpendicular e paralela às frentes. Ao longo de 8 anos mais 96.000 frentes oceânicas foram detectadas, co-localizadas com a disponibilidade de dados de vento dando origem a 40.000 composições. O sistema de coordenadas dessas composições foi rotacionado para que as frentes oceânicas tivessem a mesma orientação. Nós empilhamos as composições em um arranjo 3D e foram obtidas médias das circulações atmosféricas induzidas. As perturbações médias obtidas indicaram que há convergência do vento quando este sopra do lado quente para o lado frio da frente com a frenagem do escoamento. De forma oposta, há divergência e aceleração do vento quando este sopra no sentido oposto. Nós identificamos alterações locais no rotacional do campo de vento capazes de induzir o bombeamento de Ekman no oceano. Esse processo pode gerar mecanismos de retroalimentação no sistema. Nossos resultados corroboram o de diversos estudos sobre o tema presentes literatura. / The southwest Atlantic circulation patterns are characterized by a diversity of water masses. The presence of currents associated with the subtropical gyre and the northward incursion of Antarctic Circumpolar Current (ACC) determine extensive regions of strong sea surface temperature gradient (SST). At the same time, mesoscale circulations generate intense local gradients, or reinforce the large-scale contrast. Consequently, oceanic fronts are formed along these gradients on different scales. When the wind blows over these fronts, the fluids exchange heat and momentum, and that changes their dynamic and thermodynamic properties. In this work we aim to characterize the changes in the surface wind field that might be attributed to these exchanges. To do it, a frontal detection algorithm was applied to the SST field derived from OSTIA set. We selected situations of synoptic homogeneous atmospheric flow and calculated the divergent and rotational wind, in addition to its perpendicular and parallel components to the oceanic fronts. We used wind measurements recorded by the QuickSCAT scatterometer along the frontal zones. More than 96,000 oceanic fronts were detected along 8 years of data. We matched them to available wind data and formed more than 40,000 SST-WIND compositions. The coordinate system of these compositions was rotated so that all oceanic fronts have the same horizontal orientation. We piled up the compositions in a 3D array and the temporal mean of the induced circulations was calculated. The average disturbance obtained indicated that there is wind convergence when it blows from the warm side of the front to the cold side because the flow is slowed down. Conversely, there is wind divergence when it blows in the opposite direction due to speeding up flow. We identified local changes in wind field curl capable of inducing Ekman pumping over the ocean. This process can generate feedback mechanisms in the system. Our results were consistent with the literature.

Les derniers 22 kans sont marqués par des évènements climatiques rapides, non synchrones entre l‘hémisphère Sud et le Nord. Un mécanisme de bascule des températures polaires, amplifié par la capacité de l‘océan profond à stocker et à restituer une partie du CO₂ atmosphérique en fonction de l‘intensité de la circulation océanique et des upwellings le long de la divergence Australe, a été proposé pour expliquer ces évènements. L‘objectif principal de cette thèse a été de définir quel est le rôle de l‘Océan Austral durant ces variations climatiques rapides à l‘aide de 3 carottes sédimentaires marines, prélevées le long de la marge chilienne, sous l‘influence des fronts océaniques et des vents d‘Ouest. La reconstitution des températures océaniques de surface (SST) ont permis de retracer l‘évolution du gradient latitudinal de SST au cours des derniers 22 kans mettant en évidence des migrations vers le sud du front Subtropical, notamment durant la déglaciation,marqués par des changements faunistiques en foraminifères planctoniques et benthiques suggérant unapport accru de nutriments en surface, et accompagnés par un enrichissement en [O₂] dans l‘eau de fond. Ces évènements sont peut-être liés à un renforcement des upwellings au niveau de la divergence australe induisant un renforcement de la ventilation des eaux intermédiaires antarctiques. Ces variations hydrologiques se produisent durant la hausse de CO₂ atmosphérique enregistrée dans les carottes de glace antarctiques pendant la déglaciation, indiquant un lien intime entre les upwellings, l‘intensité de la ventilation des eaux intermédiaires et le transfert de CO₂ depuis l‘océan profond vers l‘atmosphère. / The last 22 kyr are marked by abrupt climatic events, non-synchronous between the southern and northern hemispheres. A see-saw mechanism of the polar temperatures, amplified by the deep oceanability to store and release a portion of atmospheric CO₂, depending on the intensity of the thermohaline circulation and the large upwellings along the southern divergence, has been proposed to explain these observations. The main aim of this thesis was to assess the role of the southern ocean during these millennial events, by studying 3 marine cores, retrieved along the Chilean margin, under the influence of oceanic fronts and the westerly winds. The reconstruction of the sea surface temperatures (SST) allowed tracing the evolution of the SST latitudinal gradient during the last 22 kyr, highlighting southward migrations of the Subtropical Front, especially during the deglaciation, marked by benthic and planktonic foraminifera faunal changes which can be interpreted as surface nutrients inputs increase, accompanied by an enrichment of the bottom water [O₂] in the bottom water. These events could be related to stronger upwellings at the southern divergence leading to an increase of the Antarctic intermediate waters ventilation. These changes occur during atmospheric CO₂ increases recorded in Antarctic ice cores, marking the deglaciation, and suggesting an intimate link between upwellings, the intensity of the intermediate waters ventilation, and deep ocean-atmosphere CO₂ transfers.

A dinâmica da matéria orgânica particulada (MOP) nos oceanos, desde sua formação até seu consumo/exportação, é um elo importante no ciclo biogeoquímico do carbono e elementos associados, que ganhou importância nas últimas décadas devido ao aumento do CO2 antropogênico. Para melhorar os modelos e as previsões climáticas, projetos oceanográficos investigam os fatores que influenciam na dinâmica da MOP, sobretudo em regiões produtivas e representativas em escala global. No Atlântico Sul, a região mais produtiva é ao largo do continente africano, devido à contínua ressurgência de borda leste. Entretanto, regiões hidrograficamente dinâmicas também podem contribuir com elevadas taxas de produção dependendo das condições ambientais, cuja importância no reservatório de MOP ainda é desconhecida. Este trabalho tem como objetivo estudar a dinâmica do MOP em suspensão em duas regiões também produtivas do Atlântico Sudoeste: (i) o setor externo da Margem Continental Sudeste Brasileira (Capítulo 1); e (ii) o setor Austral ao sul de 30ºS (Capítulo 2). São discutidos os efeitos das condições oceanográficas no reservatório de MOP e seus padrões interanuais de distribuição geográfica. / The dynamics of particulate organic matter (POM) in the oceans, from its formation to its consumption/export, is an important link in the biogeochemical cycle of carbon and associated elements, which gained importance in the last decades due to increase of anthropogenic CO2. To improve models and climate predictions, oceanographic projects investigate the factors that influence the POM dynamics, especially in productive and representative regions on a global scale. In the South Atlantic, the most productive region is off the African continent, due to permanent Eastern Boundary upwelling. However, dynamic hydrographic regions can also provide with high production rates depending on environmental conditions, whose importance in the POM reservoir is still unknown. This work aims to study the suspended POM dynamics in two productive regions of the southwest Atlantic: (i) the outer Brazilian Southeast Continental Margin (Chapter 1); and (ii) the Austral sector south of 30ºS(Chapter 2). The effects of different oceanographic conditions in the POM reservoir, their interannual pattern and geographic distribution are discussed.

A dinâmica da matéria orgânica particulada (MOP) nos oceanos, desde sua formação até seu consumo/exportação, é um elo importante no ciclo biogeoquímico do carbono e elementos associados, que ganhou importância nas últimas décadas devido ao aumento do CO2 antropogênico. Para melhorar os modelos e as previsões climáticas, projetos oceanográficos investigam os fatores que influenciam na dinâmica da MOP, sobretudo em regiões produtivas e representativas em escala global. No Atlântico Sul, a região mais produtiva é ao largo do continente africano, devido à contínua ressurgência de borda leste. Entretanto, regiões hidrograficamente dinâmicas também podem contribuir com elevadas taxas de produção dependendo das condições ambientais, cuja importância no reservatório de MOP ainda é desconhecida. Este trabalho tem como objetivo estudar a dinâmica do MOP em suspensão em duas regiões também produtivas do Atlântico Sudoeste: (i) o setor externo da Margem Continental Sudeste Brasileira (Capítulo 1); e (ii) o setor Austral ao sul de 30ºS (Capítulo 2). São discutidos os efeitos das condições oceanográficas no reservatório de MOP e seus padrões interanuais de distribuição geográfica. / The dynamics of particulate organic matter (POM) in the oceans, from its formation to its consumption/export, is an important link in the biogeochemical cycle of carbon and associated elements, which gained importance in the last decades due to increase of anthropogenic CO2. To improve models and climate predictions, oceanographic projects investigate the factors that influence the POM dynamics, especially in productive and representative regions on a global scale. In the South Atlantic, the most productive region is off the African continent, due to permanent Eastern Boundary upwelling. However, dynamic hydrographic regions can also provide with high production rates depending on environmental conditions, whose importance in the POM reservoir is still unknown. This work aims to study the suspended POM dynamics in two productive regions of the southwest Atlantic: (i) the outer Brazilian Southeast Continental Margin (Chapter 1); and (ii) the Austral sector south of 30ºS(Chapter 2). The effects of different oceanographic conditions in the POM reservoir, their interannual pattern and geographic distribution are discussed.