Um modelo paramétrico regional tridimensional da Corrente do Brasil (CB) foi construído com o objetivo de investigar se o meandramento frontal da CB domina a variabilidade subinercial na Bacia de Campos. A parametrização da CB normal à costa seguiu a formulação proposta por Schmidt et al. [2007]. Os parâmetros da CB foram estimados a partir dos perfis de velocidade quase-sinóticos durante a amostragem do cruzeiro OCEANO SUDESTE II (OCSEII) da Marinha do Brasil. A frente térmica costeira (FTC), facilmente detectado na superfície do mar por imagens de satélite, é tida como a fronteira costeira do CB com velocidades desprezíveis. A FTC padrão é, então, inferida pelo método do gradiente máximo em uma data escolhida. Com a localização da FTC, várias radiais são projetadas normalmente à frente e os perfis de velocidades da CB são ajustados a estas radiais. O próximo passo é interpolar objetivamente o campo de velocidade para obter uma CB tridimensional. A variabilidade espacial da CB neste mapa é, portanto, unicamente devido à arqueamento da velocidade/ FTC, e os padrões de velocidade são devidos apenas ao meandramento frontal. Estes foram identificados nas séries temporais das FTC e o modelo foi computado para dois eventos separados no inverno de 2007 e comparados com os dados de ADCPs da PETROBRAS montados em quatro plataformas de petróleo. A comparação foi feita usando compósitos semanais e médias para isolar movimentos de mesoescala. Isso mostra que há um acordo muito favorável entre o modelo e as medições de velocidade de mar aberto em ambas as magnitudes e direções. Este assegura que os meandros frontais, ou mais especificamente, o meandro de São Tomé domina a variabilidade subinercial ao longo do talude continental e do platô de São Paulo. A única exceção é para o ADCP montado sobre uma plataforma de petróleo em plataforma continental. O modelado e as observações in situ discordam e indicam que outros fenômenos, tais como ondas de plataforma, devem ser contabilizados na parte costeira / A regional three-dimensional parametric model of the Brazil Current (BC) was built with the goal of investigating whether or not the BC frontal meandering dominates the subinercial current variability in the Campos Basin. The BC cross-stream parametrization followed the formulation proposed by Schmidt et al. [2007]. The BC parameters were estimated from quasi-synoptic velocity profiling sampled during the Brazilian Navy cruise OCEANO SUDESTE II (OCSEII). The surface inshore thermal front (ITF),easily detected in sea surface temperature satellite images, is taken as the inshore border of the BC jet with negligible velocities. The ITF spatial pattern is then inferred by the maximum gradient method on a chosen date or period. With the ITF location, several BC cross-strem profiles are projected normally to it. The next step is to objectively interpolate the velocity field to obtain a three-dimensional BC. The spatial variability of the BC in this map is therefore solely due to the arching of the velocity/ITF front, and therefore, the velocity patterns are due to frontal meandering only. Meandering events were identified in the IFT time series, the model computed the BC frontal patterns for two separate events in the winter of 2007 and compared with PETROBRAS\' ADCP records mounted on four oil rigs. The comparison was done using weekly composites and averages to isolate mesoscale motions. It shows that there is a very favorable agreement between between the model and the open sea velocity measurements in both magnitude and direction. This reassures that the frontal meandering, or more specifically, the S~ao Tom´e Meander formation dominates the subinertial variability over the continental slope and the S~ao Paulo Plateau. The only exception is for the ADCP mounted on an oil rig on the continental shelf. The modeled and in situ observations disagree and indicate that other phenomena, such as shelf waves, should be accounted in the coastal ocean in addition to the BC meandering.

Um modelo paramétrico regional tridimensional da Corrente do Brasil (CB) foi construído com o objetivo de investigar se o meandramento frontal da CB domina a variabilidade subinercial na Bacia de Campos. A parametrização da CB normal à costa seguiu a formulação proposta por Schmidt et al. [2007]. Os parâmetros da CB foram estimados a partir dos perfis de velocidade quase-sinóticos durante a amostragem do cruzeiro OCEANO SUDESTE II (OCSEII) da Marinha do Brasil. A frente térmica costeira (FTC), facilmente detectado na superfície do mar por imagens de satélite, é tida como a fronteira costeira do CB com velocidades desprezíveis. A FTC padrão é, então, inferida pelo método do gradiente máximo em uma data escolhida. Com a localização da FTC, várias radiais são projetadas normalmente à frente e os perfis de velocidades da CB são ajustados a estas radiais. O próximo passo é interpolar objetivamente o campo de velocidade para obter uma CB tridimensional. A variabilidade espacial da CB neste mapa é, portanto, unicamente devido à arqueamento da velocidade/ FTC, e os padrões de velocidade são devidos apenas ao meandramento frontal. Estes foram identificados nas séries temporais das FTC e o modelo foi computado para dois eventos separados no inverno de 2007 e comparados com os dados de ADCPs da PETROBRAS montados em quatro plataformas de petróleo. A comparação foi feita usando compósitos semanais e médias para isolar movimentos de mesoescala. Isso mostra que há um acordo muito favorável entre o modelo e as medições de velocidade de mar aberto em ambas as magnitudes e direções. Este assegura que os meandros frontais, ou mais especificamente, o meandro de São Tomé domina a variabilidade subinercial ao longo do talude continental e do platô de São Paulo. A única exceção é para o ADCP montado sobre uma plataforma de petróleo em plataforma continental. O modelado e as observações in situ discordam e indicam que outros fenômenos, tais como ondas de plataforma, devem ser contabilizados na parte costeira / A regional three-dimensional parametric model of the Brazil Current (BC) was built with the goal of investigating whether or not the BC frontal meandering dominates the subinercial current variability in the Campos Basin. The BC cross-stream parametrization followed the formulation proposed by Schmidt et al. [2007]. The BC parameters were estimated from quasi-synoptic velocity profiling sampled during the Brazilian Navy cruise OCEANO SUDESTE II (OCSEII). The surface inshore thermal front (ITF),easily detected in sea surface temperature satellite images, is taken as the inshore border of the BC jet with negligible velocities. The ITF spatial pattern is then inferred by the maximum gradient method on a chosen date or period. With the ITF location, several BC cross-strem profiles are projected normally to it. The next step is to objectively interpolate the velocity field to obtain a three-dimensional BC. The spatial variability of the BC in this map is therefore solely due to the arching of the velocity/ITF front, and therefore, the velocity patterns are due to frontal meandering only. Meandering events were identified in the IFT time series, the model computed the BC frontal patterns for two separate events in the winter of 2007 and compared with PETROBRAS\' ADCP records mounted on four oil rigs. The comparison was done using weekly composites and averages to isolate mesoscale motions. It shows that there is a very favorable agreement between between the model and the open sea velocity measurements in both magnitude and direction. This reassures that the frontal meandering, or more specifically, the S~ao Tom´e Meander formation dominates the subinertial variability over the continental slope and the S~ao Paulo Plateau. The only exception is for the ADCP mounted on an oil rig on the continental shelf. The modeled and in situ observations disagree and indicate that other phenomena, such as shelf waves, should be accounted in the coastal ocean in addition to the BC meandering.

Résumé : Au-delà de tous débats scientifiques actuels, un constat unanime est certainement la réduction du couvert de glace dans l’océan Arctique, associé au réchauffement planétaire. La réduction du couvert de glace aura sans doute des impacts encore imprévisibles sur le milieu marin. Nous avons, dans ce contexte, traité des données satellitaires et des données de mesures de réalité de terrain de campagnes océanographiques dans la portion sud-est de la mer de Beaufort afin d’étudier les variabilités spatiale et temporelle de la biomasse phytoplanctonique et tenter de les relier aux processus physiques existants dans ce milieu. La mer de Beaufort étant fortement influencée par les eaux douces du fleuve Mackenzie, il était probable que les algorithmes de couleur de l’eau opérationnels actuels ne permettaient pas une estimation juste de la concentration de la chlorophylle-a (chl-a) et, par conséquent, de la production primaire qui est à la base de la chaîne alimentaire marine. L’analyse des données bio-optiques a confirmé cette hypothèse montrant une surestimation de la chl-a in situ par un facteur variant entre 3 et 5. La forte contribution de la matière organique colorée dissoute et des particules non-algales à l’absorption de la lumière apparaît comme la source principale de cette surestimation. Nous avons donc proposé des algorithmes adaptés ainsi que de nouveaux algorithmes utilisant deux rapports de bandes spectrales permettant une estimation plus précise de la chl-a dans le sud-est de la mer de Beaufort. Une comparaison entre des données de réalité de terrain et des images satellitaires a aussi montré que la réflectance normalisée à la surface de l’eau, de même que le rapport bleu-vert, étaient plus précis à l’aide des données du capteur SeaWiFS que de celles des capteurs MODIS et MERIS. Nous avons procédé à une analyse des patrons de chl-a et de température de surface pour cinq sous-régions géographiques dans la mer de Beaufort à l’aide de sept années de données satellitaires SeaWiFS et AVHRR (1998-2004). Les résultats ont montré que les variabilités spatiale, temporelle et interannuelle de la biomasse phytoplanctonique sont régies par plusieurs facteurs environnementaux affectant la stratification de la colonne d’eau, soit le forçage du vent, la dynamique de la glace, la température de l’air, l’ensoleillement et les courants marins. Une approche statistique basée sur le concept de provinces non statiques a permis de partitionner la mer de Beaufort en quatre provinces biophysiques distinctes, apportant un nouvel éclairage sur les propriétés biophysiques de cette mer. L'analyse des données a aussi permis de détecter une tendance à l'augmentation de la chl-a dans deux secteurs de la mer de Beaufort : le plateau du Mackenzie et la partie sud du golfe d'Amundsen. Finalement, une analyse de gradients spatiaux, effectuée à partir d’images de température de surface de l’eau a permis de détecter des fronts thermiques récurrents. Ces structures spatiales jouent un rôle majeur dans l’écosystème marin, en particulier en raison de leur impact sur le développement de la biomasse phytoplanctonique. Nous avons mis en évidence des nouvelles structures frontales sur le plateau du Mackenzie et dans la région de la polynie du cap Bathurst. Les nouveaux fronts détectés sont principalement reliés à des particularités bathymétriques de la région, à la présence du panache du fleuve Mackenzie ainsi qu’à la gyre de Beaufort. En conclusion, la réalisation de cette étude a permis de générer de nouvelles informations sur les interactions entre les processus physiques et biologiques, permettant ainsi de mieux appréhender les conséquences biogéochimiques et écologiques résultant des modifications climatiques dans la mer de Beaufort. // Abstract : The Arctic Ocean ecosystem is experiencing significant changes such as a drastic reduction in seasonal sea-ice cover linked to global warming. These changes are likely to modify the physics, biogeochemistry and ecology of this unique environment in ways that are yet to be understood. In this context, we processed satellite data and in situ measurements in the southeastern Beaufort Sea to explore the spatial and temporal variability of phytoplankton biomass and link it to existing physical processes in this region. The optical properties of the Beaufort Sea being under the influence of the Mackenzie River plume, it was likely that operational ocean color algorithms did not allow an accurate estimate of chlorophyll-a concentration (Chl-a) that is a key indicator of phytoplankton biomass and marine productivity. Analysis of bio-optical data confirmed this hypothesis showing an overestimation of Chl-a in situ by a factor of three to five. High contribution of colored dissolved organic matter and non algal particles to the blue light absorption appears as the source of that poor performance. We propose regionally adapted and new algorithms using ratio of two spectral bands allowing better accuracy estimation of Chl-a in the southeastern Beaufort Sea. A match-up analysis of coincident in situ data and satellite overpass showed that the normalized water-leaving reflectance and the blue-to-green ratio retrieval were more accurate for SeaWiFS data than for MODIS and MERIS data. We investigated temporal and spatial linkages between physical and biological parameters to infer the boundaries of biophysical areas in the Canadian Beaufort Sea. Monthly sea surface temperature (AVHRR) data and chlorophyll a data from SeaWiFS were collected over seven years in five geographical sub-regions in the Beaufort Sea (1998-2004). Results showed that the spatial, temporal and inter-annual variability of phytoplankton biomass are driven by several environmental factors affecting the stratification of the water column : wind forcing, ice dynamics, air temperature, irradiance and currents. A cluster analysis based on the concept of non-static provinces was used to define four biophysical provinces in this sea. Positive temporal trends were detected for Chl-a over two regions of the Beaufort Sea : the Mackenzie Shelf and the southern portion of Amundsen Gulf. Finally, an analysis of spatial gradients, using 11 years of sea surface temperature images, allowed the detection of recurrent thermal fronts. These spatial structures play a major role in the marine ecosystem, particularly because of their impact on the development of phytoplankton biomass. We highlighted new frontal structures on the Mackenzie Shelf and in the Cape Bathurst polynya area. These identified new fronts are mainly related to bathymetric features of the region, the presence of the Mackenzie River plume and the Beaufort Gyre. In conclusion, this study has generated new information on the interactions between physical and biological processes to better understand the biogeochemical and ecological consequences of climate change in the Beaufort Sea.