A Subcorrente Norte do Brasil (SNB) é a corrente de contorno oeste que fecha o Giro Equatorial do Oceano Atlantico em sua porc¸ ao austral. É uma corrente vigorosa, com núcleo atingindo 1ms1 em profundidades de 150ma 250 m. Trabalhos pretéritos reportam que esta corrente transporta mais de 20 Sv (1 Sv = 106 m3 s1). Ao receber o aporte de volume de ramos da Corrente Sul Equatorial (CSE), em torno de 4 S 5 S, a SNB adquire núucleo em superfície e passa a ser denominada Corrente Norte do Brasil (CNB). Entretanto, nao há relato do padrao contínuo da SNB entre 11 S e as proximidades da linha do equador, por observacões de velocidade, na literatura. O objetivo desta dissertação é justamente o mapeamento sinótico e descrição da SNB e das estruturas de mesoescala associadas na faixa latitudinal supracitada. Para tanto, combinamos dados de ADCP de casco e de hidrografia. Os dados sao oriundos das comissoes OCEANO NORDESTE I (ONEI, verao 2002) e OCEANO NORDESTE II (ONEII, primavera 2004), realizadas a bordo do NOc Antares da Marinha do Brasil. Através de cálculo de velocidades geostróficas relativas a 1.150 m, análise dos dados de velocidades perfiladas pelo ADCP de casco e cálculo de velocidades geostróficas absolutas referenciadas pelos dados de ADCP a 160 m, obtivemos uma descrição da SNB que confirma e estende esforços anteriores de pesquisa. A SNB aparece como uma corrente robusta e presente ao longo de todas as radiais analisadas. Entre 11 S e as proximidades do Cabo Calcanhar (RN), o comportamento da corrente revela pouco meandramento, seguindo o talude continental nordestino. A exceção é um ramo ciclonico em torno de 4 S que cede volume para originar a Subcorrente Sul Equatorial (SSE) em nível subpicnoclínico. A SNB, provalvemente tentando conservar vorticidade potencial, frente à abrupta mudança de orientação da margem continental em 5 S, também desenvolve vii um meandro anticiclonico frontal centrado na longitude da cidade de Macau (RN) e com cerca de 150 km de raio. Como há evidencia do anticiclone nas duas comissões, especulamos tratar-se de uma estrutura semipermanente. Por tratar-se de um relato original, decidimos denominá-lo Vórtice de Macau (VM). Outro resultado relevante foi a documentação do processo de transformação da SNB em CNB, com avaliação do núcleo se tornando mais raso em direção ao equador. No cenário da ONEII, observamos a retroflexao picnoclínica da CNB, ocorrida no hemisfério boreal e a origem da Subcorrente Equatorial (SE) na área de estudo. Também como resultado inédito, os dados de velocidade observada mostraram que também há cessao de volume pela SNB para SE em torno de 1 S. / The North Brazil Undercurrent (NBUC) is the western boundary current that closes the Equatorial Gyre of the Atlantic Ocean in its austral portion. The NBC is a vigorous current with a core that reaches 1 m s1 at depth of 150 m to 250 m. Previous works reported that this current transports more than 20 Sv (1 Sv = 106 m3 s1). As branches of the South Equatorial Current (SEC) reaches the western boundary at around 4 S 5 S, the NBUC core surfaces and the new current is referred as the North Brazil Current (NBC). However, there is no report in the literature about a continuous pattern of the NBUC in the latitude range between 11 S and the vicinities of the equator from observed velocities. The main goal of this thesis is just to obtain a synoptic map of NBUC and the associated mesoscale features in the latitude range mentioned above. In order to do so, we combined vessel-mount ADCP and hydrographic data from two cruises conducted by the R/V Antares of the Brazilian Navy: the OCEANO NORDESTE I (ONEI, summer 2002) and the OCEANO NORDESTE II (ONEII, spring 2004). We calculated geostrophic velocities relative to 1.150 m, analyzed ADCP observed velocity data as well computed absolute geostrophic velocities, referenced by the ADCP data at 160 m. Hence, we were able to obtain a NBC description that corroborated and extended the findings of previous research in the area. The NBUC was depicted as a robust nearly non-meandering current between 11 S and Cape Calcanhar (RN) present in all transects of both cruises. At 4 S, the NBUC develops a cyclonic branch and originates the South Equatorial Undercurrent (SEUC). Possibly as an attempt to conserve potential vorticity as the NBUC faces the abrupt change in the continental margin orientation at 5 S, the current develops a 150 km radius anticyclonic frontal meander. As there are evidence of the anticyclone ix in both cruises, we speculate that it can be a semipermanent feature. As it is a original description, we named it the Macau Eddy. Another result that deserves to be mentioned is that the process of the transformation of the NBUC in NBC was well documented for the first time through a continuous surfacing process of the current core. Finally, in the ONEII scenario, we observed the pycnoclinic retroflection of the NBC that occurs in northern hemisphere and returns to the equator to originate the Equatorial Undercurrent (EUC). We also depicted that the NBUC feeds the forming EUC from the southern hemisphere from a cyclonic branch around 1 S.

A Corrente do Brasil (CB) se origina na bifurcac¸ ao da Corrente Sul Equatorial (BiCSE), e flui para o sul ao longo da margem continental brasileira. Inferencias sobre a origem e organizac¸ ao da CB sao baseadas em padroes de grande escala associados `a estrutura da BiCSE. H´a carencia de detalhes no que tange `a rica atividade de mesoescala possivelmente envolvida em seu processo de formac¸ ao. Sao fartas as evidencias de meandros e v´ ortices da CB na literatura ao largo das costas sudeste e sul do Brasil. A costa leste, que abriga seu s´tio de origem, permanece ainda bastante desconhecida neste ponto de vista. Motivamo-nos por esta lacuna de informac¸ oes a conduzir este trabalho. Optamos primeiramente por estimar um cen´ario m´edio do escoamento geostr ´ofico associado a BiCSE e origem da CB no per´odo de verao, atrav´es de um conjunto de dados termohalinos climatol´ogicos. Objetivamos por fim, obter uma descric¸ ao sin´ otica do escoamento geostr´ofico associado ao s´tio de origem da CB. Para tanto, dispomos de um conjunto de dados composto por amostragem quase-sin´ otica de dados termohalinos (via CTD) e de velocidade (via ADCP de casco) simultaneamente, entre os paralelos de 10S e 20S. Tais observac¸ oes sao oriundas da Operac¸ ao Oceano Leste II (OEII), realizada pela Marinha do Brasil em marc¸o de 2005. Conduzimos a investigac¸ ao a partir de um m´etodo cient´fico que entendemos nao ter sido ainda empregado para os escoamentos ao largo da costa brasileira. Tal m´etodo consiste no M´etodo Dinamico Referenciado, que combina dados termohalinos e de velocidades observadas para estimar velocidades geostr´oficas absolutas, que sao livres da dependencia de um n´vel de movimento nulo imposto pelo M´etodo Dinamico Cl´assico. Este m´etodo substitui o n´vel de movimento nulo por um n´vel de velocidades conhecidas, que correspondem `as velocidades medidas diretamente pelo ADCP de casco. Encontramos para o cen´ario climatol ´ogico de verao, a assinatura da BiCSE em 9S para superf´cie, em 12S para 200 m, vi em 20S para 500 m e em 23S para 800 m. Confirmamos informac¸ oes da literatura sobre sua migrac¸ ao meridional com o aumento da profundidade. Identificamos tamb´em o cen´ario m´edio de origem e organizac¸ ao da CB e da Sub-corrente Norte do Brasil (SNB) nos n´veis citados, os quais subsidiarao a an´alise dos campos sin´ oticos. Os campos sin´oticos confirmaram os resultados m´edios da climatologia. Em superf´cie, nao observamos sinais da BiCSE no interior da ´area de estudo, e mostramos que na ocasiao da OEII, a CB se origina ao norte de 10S e comec¸a sua organizac¸ ao ainda distante da margem continental. Em 150 m, identificamos a assinatura da BiCSE em 14,5S, e em 500 m, em 20S. Sugerimos entao que a origem da CB enquanto corrente de contorno oeste, fluindo junto `a margem continental leste brasileira, se localiza em 14,5S. Concluindo, a CB se organiza ao norte de 10S e flui distante da margem continental como uma corrente fraca e rasa, atingindo no m´aximo os 100 primeiros metros de profundidade. Esta corrente atinge o contorno oeste em 14,5S e flui em direc¸ ao ao sul seguindo as isobatim´etricas. Ao longo deste caminho, apresenta meandros vigorosos, em particular, anticiclones. Estes anticiclones parecem estar associados a feic¸ oes topogr´aficas relevantes da ´area tais quais os Bancos de Royal Charlotte e de Abrolhos. As velocidades da CB aumentam em intensidade e a corrente ganha espessura vertical at´e 20S. A SNB parece se originar em 20S, com n´ ucleo situado em 700 m. Esta corrente segue viagem rumo ao norte de forma que seu n´ ucleo se torna cada vez mais raso, e suas velocidades cada vez maiores, at´e deixar o dom´nio em 10S. Nesta latitude, seu n´ ucleo se localiza a 250 m de profundidade. / The origin of Brazil Current (BC) is associated with the bifurcation of the South Equatorial Current (BiSEC). The BC then flows south bordering the Brazilian continental margin. However, inferences on the BC origin site as well as its organization as a western boundary current are based in large scale patterns of the BiSEC. It lacks details on the location of the BC and the possible mesoscale activity related to its formation. While the BC meandering off the Southeastern and Southern Brazilian continental margin has been widely reported in the literature, no information is available for the BC structure and its meanders off the Brazilian Eastern margin. The motivation and main goal of this work is to describe the mesoscale scenario associated with the BC formation and organization as a boundary current. In order to reach this goal, we opted to first build a climatological geostrophic picture of the BiSEC and BC origin for the summer using solely temperature-salinity data. Following such investigation, we analyzed data from an oceanographic cruise conducted by the Brazilian Navy that consisted of simultaneous CTD profiling and vessel-mounted ADCP velocity measurements, also for the summer period. The quasi-synoptic data analysis was conducted using a method that has not been employed for flows along the Brazilian continental margin: the ADCP-referenced dynamic method. Unlike the traditional dynamic method, ADCP velocities are used to reference the CTD-derived baroclinic velocities and to obtain a total geostrophic velocity field. In the climatological data analysis, the relative geostrophic current patterns exhibited a BiSEC signature at 9S for surface, at 12S for 200 m, at 20S for 500 m and 23S for 800 m. We thus confirmed information of the literature about the southward migration of the BiSEC structure with depth. We also identified the summer mean scenario for the BC and North Brazil Undercurrent (NBUC) formation. The quasi-synoptic total velocity fields confirmed the relative cliviii matological fields. At surface, we found no signature of the BiSEC within the cruise sampled area. The BC was originated north of 10S and seemed to start flowing, as a weak current with vertical extension less than 100 m deep, distant from the western boundary. At 150 m (500 m), the BiSEC signature was evident at 14.5S (20S). We thus suggest that the synoptic BC origin as a western boundary current was located at around 14.5S. We can summarize our findings describing that the BC organized itself as a weak and shallow current at around 10S. At 14.5S, the BC attached itself to the continental margin and flew following the bathymetric contours. As it flows south, it meandered vigorously and frontal anticyclones were present off the main topographic features of the Eastern coast: the Royal Charlotte and the Abrolhos Banks. In its path southward, the BC was intensified and extended vertically. It seemed that NBUC was originated at around 20S with a velocity core centered at 700 m. As this undercurrent flows northward, it increased transport and its velocity core became shallower. At the northern portion of the study area, the NBUC core reached the depth of 250 m.

Made available in DSpace on 2015-03-13T17:08:34Z (GMT). No. of bitstreams: 1 CamilaHCS_DISSERT.pdf: 5199158 bytes, checksum: 3fe566edfdb484ed92ea990061bd1ccd (MD5) Previous issue date: 2012-02-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The aim of this study was the seasonal characterization of the morphology, sedimentology and hydrodynamic of the A?u, Cavalos and Conchas estuaries. These estuaries are inserted in a semi-arid climate area and form the mouth of the hydrographic basin of the Piranhas-A?u river, that represent the discharge of the largest watershed in the state. They are embedded in an environment consisting of a fluvial-marine floodplain, mangrove ecosystem, sandbanks, fields of dunes, spits and sandy beaches. Adjacent to the natural units are the main local socioeconomic activities (oil industry, salt industry, shrimp farming, fishing and tourism) are dependent on this river and its conservation. The environmental monitoring is necessary because it is an area under constant action of coastal processes and at high risk of oil spill. The acquisition and interpretation of hydrodynamic, sonographic and sediment data was conducted in two campaigns, dry season (2010) and rainy season (2011), using respectively the current profiler ADCP Doppler effect, the side-scan sonar and Van Veen sampler. In these estuaries: A?u, Cavalos and Conchas were identified the following types of bedforms: flatbed and Dunes 2-D and 3-D (small to medium size), generated at lower flow regime (Froude number <1). Structures such as ripples were observed in the A?u estuary mouth. The higher values of flow discharge and velocity were recorded in the A?u estuary (434,992 m?.s-? and 0,554 m.s-?). In rainy season, despite the record of highest values of discharge and flow velocities at the mouth, the energy rates upstream did not differ much from the data of the dry season. However, in all estuaries were recorded an increase in speed and flow, with reservation to the flow in the A?u estuary and flow at the mouth of the Conchas estuary. Sediment grain sizes tend to increase towards the mouth of the estuary and these ranged from very fine sand to very coarse sand, medium sand fraction being the most recurrent. Based on the data acquired and analyzed, the estuaries A?u, Cavalos and Conchas are classified as mixed , dominated by waves and tides. According to their morphology, they are classified as estuaries constructed by bar and according to the classification by salinity, estuaries Conchas and Cavalos were ranked as hypersaline estuaries, and A?u as hypersaline and vertically well mixed type C / Este trabalho teve como objetivo a caracteriza??o sazonal da morfologia, sedimentologia e hidrodin?mica dos estu?rios A?u, Cavalos e Conchas. Estes estu?rios est?o inseridos numa regi?o semi-?rida e comp?e a desembocadura do Rio Piranhas-A?u, maior bacia hidrogr?fica do Estado do Rio Grande do Norte. Compreendem um ambiente constitu?do por plan?cie de inunda??o fl?vio-marinha, ecossistema de manguezal, bancos arenosos, campos de dunas, pontais e praias arenosas, onde os processos costeiros atuantes s?o ressaltados principalmente pela din?mica das modifica??es nas estruturas morfol?gicas ali presentes. Adjacente as unidades naturais, as principais atividades socioecon?micas locais s?o constituidas pela ind?stria petrol?fera, salineira, carcinicultura, pesqueira e tur?stica, tamb?m dependentes deste rio e da sua conserva??o. O monitoramento ambiental desta regi?o se faz portanto necess?rio por se tratar de uma ?rea sob constante a??o dos processos costeiros e com alto risco ao derramamento de ?leo. A aquisi??o de dados hidrodin?micos, sonogr?ficos e sedimentol?gicos foi realizada em duas campanhas: uma no per?odo seco de 2010 e outra no per?odo chuvoso de 2011, utilizando respectivamente, perfilador de correntes por efeito Doppler- ADCP, sonar de varredura lateral e amostrador pontual Van Veen. Nestes estu?rios foram identificadas fei??es de fundo do tipo Leito Plano e Dunas 2-D e 3-D (pequeno a m?dio porte), geradas em regime de fluxo inferior (n?mero de Froude <1). Estruturas do tipo marcas onduladas (ripples) foram observadas somente na foz do estu?rio A?u. Os maiores valores de vaz?o e velocidade do fluxo foram registrados no estu?rio A?u (434,992 m?.s-? e 0,554 m.s-?). No per?odo chuvoso foram registrados os maiores valores de descarga e velocidades do fluxo na regi?o da foz. Entretanto, na montante as taxas de energia n?o diferenciaram muito dos dados obtidos no per?odo seco. Contudo, foi registrado nos tr?s estu?rios um aumento na velocidade e na vaz?o durante o per?odo chuvoso, com ressalva na vaz?o no estu?rio A?u e na vaz?o na foz do estu?rio Conchas. Os sedimentos presentes nos estu?rios variaram de areia muito fina a areia muito grossa, sendo a fra??o areia m?dia a mais recorrente. Em geral a granulometria aumentou em dire??o a foz dos estu?rios. Com base na an?lise e interpreta??o dos dados adquiridos os estu?rios A?u, Cavalos e Conchas foram classificados como dominados por processos misto de ondas e mar?s. De acordo com a morfologia foram classificados como estu?rios constru?dos por barra e segundo a classifica??o por salinidade, os estu?rios A?u, Cavalos e Conchas foram classificados como estu?rios hipersalinos. Adicionalmente o estu?rio A?u tamb?m foi classificado como verticalmente bem misturado do tipo C

A Subcorrente Norte do Brasil (SNB) é a corrente de contorno oeste que fecha o Giro Equatorial do Oceano Atlantico em sua porc¸ ao austral. É uma corrente vigorosa, com núcleo atingindo 1ms1 em profundidades de 150ma 250 m. Trabalhos pretéritos reportam que esta corrente transporta mais de 20 Sv (1 Sv = 106 m3 s1). Ao receber o aporte de volume de ramos da Corrente Sul Equatorial (CSE), em torno de 4 S 5 S, a SNB adquire núucleo em superfície e passa a ser denominada Corrente Norte do Brasil (CNB). Entretanto, nao há relato do padrao contínuo da SNB entre 11 S e as proximidades da linha do equador, por observacões de velocidade, na literatura. O objetivo desta dissertação é justamente o mapeamento sinótico e descrição da SNB e das estruturas de mesoescala associadas na faixa latitudinal supracitada. Para tanto, combinamos dados de ADCP de casco e de hidrografia. Os dados sao oriundos das comissoes OCEANO NORDESTE I (ONEI, verao 2002) e OCEANO NORDESTE II (ONEII, primavera 2004), realizadas a bordo do NOc Antares da Marinha do Brasil. Através de cálculo de velocidades geostróficas relativas a 1.150 m, análise dos dados de velocidades perfiladas pelo ADCP de casco e cálculo de velocidades geostróficas absolutas referenciadas pelos dados de ADCP a 160 m, obtivemos uma descrição da SNB que confirma e estende esforços anteriores de pesquisa. A SNB aparece como uma corrente robusta e presente ao longo de todas as radiais analisadas. Entre 11 S e as proximidades do Cabo Calcanhar (RN), o comportamento da corrente revela pouco meandramento, seguindo o talude continental nordestino. A exceção é um ramo ciclonico em torno de 4 S que cede volume para originar a Subcorrente Sul Equatorial (SSE) em nível subpicnoclínico. A SNB, provalvemente tentando conservar vorticidade potencial, frente à abrupta mudança de orientação da margem continental em 5 S, também desenvolve vii um meandro anticiclonico frontal centrado na longitude da cidade de Macau (RN) e com cerca de 150 km de raio. Como há evidencia do anticiclone nas duas comissões, especulamos tratar-se de uma estrutura semipermanente. Por tratar-se de um relato original, decidimos denominá-lo Vórtice de Macau (VM). Outro resultado relevante foi a documentação do processo de transformação da SNB em CNB, com avaliação do núcleo se tornando mais raso em direção ao equador. No cenário da ONEII, observamos a retroflexao picnoclínica da CNB, ocorrida no hemisfério boreal e a origem da Subcorrente Equatorial (SE) na área de estudo. Também como resultado inédito, os dados de velocidade observada mostraram que também há cessao de volume pela SNB para SE em torno de 1 S. / The North Brazil Undercurrent (NBUC) is the western boundary current that closes the Equatorial Gyre of the Atlantic Ocean in its austral portion. The NBC is a vigorous current with a core that reaches 1 m s1 at depth of 150 m to 250 m. Previous works reported that this current transports more than 20 Sv (1 Sv = 106 m3 s1). As branches of the South Equatorial Current (SEC) reaches the western boundary at around 4 S 5 S, the NBUC core surfaces and the new current is referred as the North Brazil Current (NBC). However, there is no report in the literature about a continuous pattern of the NBUC in the latitude range between 11 S and the vicinities of the equator from observed velocities. The main goal of this thesis is just to obtain a synoptic map of NBUC and the associated mesoscale features in the latitude range mentioned above. In order to do so, we combined vessel-mount ADCP and hydrographic data from two cruises conducted by the R/V Antares of the Brazilian Navy: the OCEANO NORDESTE I (ONEI, summer 2002) and the OCEANO NORDESTE II (ONEII, spring 2004). We calculated geostrophic velocities relative to 1.150 m, analyzed ADCP observed velocity data as well computed absolute geostrophic velocities, referenced by the ADCP data at 160 m. Hence, we were able to obtain a NBC description that corroborated and extended the findings of previous research in the area. The NBUC was depicted as a robust nearly non-meandering current between 11 S and Cape Calcanhar (RN) present in all transects of both cruises. At 4 S, the NBUC develops a cyclonic branch and originates the South Equatorial Undercurrent (SEUC). Possibly as an attempt to conserve potential vorticity as the NBUC faces the abrupt change in the continental margin orientation at 5 S, the current develops a 150 km radius anticyclonic frontal meander. As there are evidence of the anticyclone ix in both cruises, we speculate that it can be a semipermanent feature. As it is a original description, we named it the Macau Eddy. Another result that deserves to be mentioned is that the process of the transformation of the NBUC in NBC was well documented for the first time through a continuous surfacing process of the current core. Finally, in the ONEII scenario, we observed the pycnoclinic retroflection of the NBC that occurs in northern hemisphere and returns to the equator to originate the Equatorial Undercurrent (EUC). We also depicted that the NBUC feeds the forming EUC from the southern hemisphere from a cyclonic branch around 1 S.

A Corrente do Brasil (CB) se origina na bifurcac¸ ao da Corrente Sul Equatorial (BiCSE), e flui para o sul ao longo da margem continental brasileira. Inferencias sobre a origem e organizac¸ ao da CB sao baseadas em padroes de grande escala associados `a estrutura da BiCSE. H´a carencia de detalhes no que tange `a rica atividade de mesoescala possivelmente envolvida em seu processo de formac¸ ao. Sao fartas as evidencias de meandros e v´ ortices da CB na literatura ao largo das costas sudeste e sul do Brasil. A costa leste, que abriga seu s´tio de origem, permanece ainda bastante desconhecida neste ponto de vista. Motivamo-nos por esta lacuna de informac¸ oes a conduzir este trabalho. Optamos primeiramente por estimar um cen´ario m´edio do escoamento geostr ´ofico associado a BiCSE e origem da CB no per´odo de verao, atrav´es de um conjunto de dados termohalinos climatol´ogicos. Objetivamos por fim, obter uma descric¸ ao sin´ otica do escoamento geostr´ofico associado ao s´tio de origem da CB. Para tanto, dispomos de um conjunto de dados composto por amostragem quase-sin´ otica de dados termohalinos (via CTD) e de velocidade (via ADCP de casco) simultaneamente, entre os paralelos de 10S e 20S. Tais observac¸ oes sao oriundas da Operac¸ ao Oceano Leste II (OEII), realizada pela Marinha do Brasil em marc¸o de 2005. Conduzimos a investigac¸ ao a partir de um m´etodo cient´fico que entendemos nao ter sido ainda empregado para os escoamentos ao largo da costa brasileira. Tal m´etodo consiste no M´etodo Dinamico Referenciado, que combina dados termohalinos e de velocidades observadas para estimar velocidades geostr´oficas absolutas, que sao livres da dependencia de um n´vel de movimento nulo imposto pelo M´etodo Dinamico Cl´assico. Este m´etodo substitui o n´vel de movimento nulo por um n´vel de velocidades conhecidas, que correspondem `as velocidades medidas diretamente pelo ADCP de casco. Encontramos para o cen´ario climatol ´ogico de verao, a assinatura da BiCSE em 9S para superf´cie, em 12S para 200 m, vi em 20S para 500 m e em 23S para 800 m. Confirmamos informac¸ oes da literatura sobre sua migrac¸ ao meridional com o aumento da profundidade. Identificamos tamb´em o cen´ario m´edio de origem e organizac¸ ao da CB e da Sub-corrente Norte do Brasil (SNB) nos n´veis citados, os quais subsidiarao a an´alise dos campos sin´ oticos. Os campos sin´oticos confirmaram os resultados m´edios da climatologia. Em superf´cie, nao observamos sinais da BiCSE no interior da ´area de estudo, e mostramos que na ocasiao da OEII, a CB se origina ao norte de 10S e comec¸a sua organizac¸ ao ainda distante da margem continental. Em 150 m, identificamos a assinatura da BiCSE em 14,5S, e em 500 m, em 20S. Sugerimos entao que a origem da CB enquanto corrente de contorno oeste, fluindo junto `a margem continental leste brasileira, se localiza em 14,5S. Concluindo, a CB se organiza ao norte de 10S e flui distante da margem continental como uma corrente fraca e rasa, atingindo no m´aximo os 100 primeiros metros de profundidade. Esta corrente atinge o contorno oeste em 14,5S e flui em direc¸ ao ao sul seguindo as isobatim´etricas. Ao longo deste caminho, apresenta meandros vigorosos, em particular, anticiclones. Estes anticiclones parecem estar associados a feic¸ oes topogr´aficas relevantes da ´area tais quais os Bancos de Royal Charlotte e de Abrolhos. As velocidades da CB aumentam em intensidade e a corrente ganha espessura vertical at´e 20S. A SNB parece se originar em 20S, com n´ ucleo situado em 700 m. Esta corrente segue viagem rumo ao norte de forma que seu n´ ucleo se torna cada vez mais raso, e suas velocidades cada vez maiores, at´e deixar o dom´nio em 10S. Nesta latitude, seu n´ ucleo se localiza a 250 m de profundidade. / The origin of Brazil Current (BC) is associated with the bifurcation of the South Equatorial Current (BiSEC). The BC then flows south bordering the Brazilian continental margin. However, inferences on the BC origin site as well as its organization as a western boundary current are based in large scale patterns of the BiSEC. It lacks details on the location of the BC and the possible mesoscale activity related to its formation. While the BC meandering off the Southeastern and Southern Brazilian continental margin has been widely reported in the literature, no information is available for the BC structure and its meanders off the Brazilian Eastern margin. The motivation and main goal of this work is to describe the mesoscale scenario associated with the BC formation and organization as a boundary current. In order to reach this goal, we opted to first build a climatological geostrophic picture of the BiSEC and BC origin for the summer using solely temperature-salinity data. Following such investigation, we analyzed data from an oceanographic cruise conducted by the Brazilian Navy that consisted of simultaneous CTD profiling and vessel-mounted ADCP velocity measurements, also for the summer period. The quasi-synoptic data analysis was conducted using a method that has not been employed for flows along the Brazilian continental margin: the ADCP-referenced dynamic method. Unlike the traditional dynamic method, ADCP velocities are used to reference the CTD-derived baroclinic velocities and to obtain a total geostrophic velocity field. In the climatological data analysis, the relative geostrophic current patterns exhibited a BiSEC signature at 9S for surface, at 12S for 200 m, at 20S for 500 m and 23S for 800 m. We thus confirmed information of the literature about the southward migration of the BiSEC structure with depth. We also identified the summer mean scenario for the BC and North Brazil Undercurrent (NBUC) formation. The quasi-synoptic total velocity fields confirmed the relative cliviii matological fields. At surface, we found no signature of the BiSEC within the cruise sampled area. The BC was originated north of 10S and seemed to start flowing, as a weak current with vertical extension less than 100 m deep, distant from the western boundary. At 150 m (500 m), the BiSEC signature was evident at 14.5S (20S). We thus suggest that the synoptic BC origin as a western boundary current was located at around 14.5S. We can summarize our findings describing that the BC organized itself as a weak and shallow current at around 10S. At 14.5S, the BC attached itself to the continental margin and flew following the bathymetric contours. As it flows south, it meandered vigorously and frontal anticyclones were present off the main topographic features of the Eastern coast: the Royal Charlotte and the Abrolhos Banks. In its path southward, the BC was intensified and extended vertically. It seemed that NBUC was originated at around 20S with a velocity core centered at 700 m. As this undercurrent flows northward, it increased transport and its velocity core became shallower. At the northern portion of the study area, the NBUC core reached the depth of 250 m.

L'objectif principal de cette thèse est d'étudier la dynamique des flux hydrosédimentaires dans le bas cours de l'Orénoque à partir de la mise en œuvre de diverses techniques qui combinent directement la mesure des données in situ et la modélisation par séries chronologiques d'images satellites. Cette thèse aborde pour la première fois trois méthodologies complémentaires pour analyser les flux hydrosédimentaires dans les grands fleuves : (i) un algorithme d'inversion robuste pour l'estimation de MES à l'aide de données Landsat-8(OLI)permet de suivre de façon systématique et fiable les variations spatio-temporelles des flux hydro-sédimentaires de surface, (ii) de même, il a été montré qu'il existe une forte relation entre le coefficient de rétrodiffusion du radar (images Sentinel-1) et les segments fluviaux d'écoulement turbulent. Cette nouvelle utilisation du radar en complément des approches classiques en géomorphologie et hydro-sédimentologie permet d'identifier des sections du fleuve où les MES sont homogénéisées, ce qui est fondamental pour le calcul des flux hydro-sédimentaires en suspension, enfin, (iii) une troisième méthodologie a été mise en œuvre pour mesurer durant le cycle hydrologique, les modifications géomorphologiques d'une île semi-submergée au centre du chenal principal. Grace à des séries topo-bathymétriques fines, associées à une modélisation 3D, l'on peut dorénavant quantifier le charriage de fond. Ces trois approches combinées permettent une évaluation plus précise du bilan hydro-sédimentaire en tenant compte des matières en suspension comme du charriage de fond. Ces études pourront servir aux gestionnaires du fleuve, confrontés à de complexes, lourdes et couteuses opérations de dragage périodiques pour maintenir sa navigabilité, ce qui est d'extrême importance pour les projets de développement socio-économiques de la frange pétrolière du bas cours de l'Orénoque. / The main objective of this thesis is to study the dynamics of hydro-sedimentary flows in the lower Orinoco from the implementation of various techniques that directly combine the measurement of in situ data and the modelling of time series of satellite images. This thesis addresses for the first time three complementary methodologies for the analysis of hydro-sedimentary flows in large rivers: i) a robust inversion algorithm for estimating suspended sediment concentration (SSC) using Landsat-8 (OLI) satellite data allows a systematic and reliable monitoring of spatial and temporal variations of surface hydro-sedimentary flows, (ii) it was shown that there is a strong relationship between the radar backscatter coefficient (Sentinel-1 images) and the turbulent flow segments in the river. This new use of radar, in addition to traditional geomorphological and hydro- sedimentological approaches, allows the identification of river sections in which suspended sediments are homogenized, which is fundamental for the calculation of suspended hydro-sedimentary flows, and finally (iii) a third methodology has been implemented to measure during the hydrological regime the geomorphological modifications of a semi-submerged island in the center of the mainstream. Thanks to a high spatial resolution topo-bathymetric series, combined with 3D modeling, it is now possible to quantify and to gain better understanding of river bed transport. These three combined approaches allow a more accurate evaluation of the hydro-sedimentary equilibrium taking into account suspended solids as well as bedload. These studies can be used by those responsible for river management, who face complex, heavy and costly periodic dredging operations to maintain their navigability, which is of extreme importance for socio-economic development projects in the Orinoco oil belt in the lower Orinoco.

In glacierised regions, suspended sediment fluxes are highly responsive to climate-driven environmental change and can provide important information regarding the relationships between glacier variations, climate and geomorphic change. As a result, understanding patterns of suspended sediment transport and their relationship with meltwater delivery is of critical importance. However, studies of glacial suspended sediment transport are often limited by interpreting patterns of suspended sediment transfer based on whole-season data, allowing precise patterns to become masked. This thesis aims to contribute to the understanding of suspended sediment transfer in glacierised basins through the investigation of patterns of suspended sediment delivery to the proglacial area of Storglaciären, a small polythermal valley glacier located in the Tarfala valley, Arctic Sweden. High temporal resolution discharge and suspended sediment concentration data were collected during two summer field campaigns at Storglaciären. Interpretations of suspended sediment transport data were made using diurnal hysteresis and sediment availability data, combined with suspended sediment shape and magnitude data classified by applying principal component and hierarchical cluster analyses. Analysis of the dominant discharge generating processes at Storglaciären was also conducted using principal component analysis, allowing patterns of discharge to be better understood. This was complemented by analysis of the structure and evolution of the glacier drainage system by linear reservoir modelling and flow recession analysis. The results suggest that patterns of discharge and suspended sediment transport at Storglaciären are complex, with distinct processes and magnitudes of transport evident at both proglacial outlet streams, Nordjåkk and Sydjåkk. These processes are intrinsically linked to meteorological variables, with both ablation-driven and precipitation-driven discharge exerting influence over patterns of suspended sediment transport in the proglacial area of Storglaciären.

This study investigates the complex flow structure generated by riparian emergent vegetation along the edge of floodplain. Detailed velocity and boundary shear stress measurements were carried out for various arrangements of emergent rigid cylindric rods of 3 mm, 6 mm and 9 mm diameters and for three different rod densities. In addition, the impact of foliage on the flow field was assessed during a series of experiments where brushes were used instead of smooth rods. The results of these new experiments are first presented. In addition to the laboratory data, field data was obtained through Acoustic Doppler Current Profiler measurements for two flood events in a stretch of the river Rhône that can be approximated to a straight compound channel with vegetated banks. The analysis of the flow structure highlights the presence of strong secondary circulation and increased vorticity on the river banks. The rods on the edge of the floodplain increase significantly flow resistance, reducing velocity and decreasing boundary shear stress. Flow rate was seen to decrease with increasing vegetative density for all cases except when foliage was added. This suggests that an optimum threshold density, for which a smaller density would lead to an increased flow rate might exist. Wakes trailing downstream of the vegetation stem, planform coherent structures advected between the main channel and the floodplain, and eddying motion in the flow due to enhanced turbulence anisotropy are among the defining patterns observed in the studied compound channel flows with one line of emergent vegetation along the edge of the floodplain. The Shiono and Knight Method (SKM) was modified in order to account for the increased turbulence activity due to the rods. The drag force term was introduced in the same way as in the work of Rameshwaran and Shiono (2007). However, a new term was added to the transverse shear stress term in the form of an Elder formulation, incorporating a friction drag coefficient which can be derived from the experimental data. In this proposed version, the advection term was set to zero. Another version of the SKM, similar to Rameshwaran and Shiono (2007), was also tested with the addition of a local drag friction only applied in the rod region. The proposed SKM version without the advection term was favored as it can be more closely related to the experimental data and to physical processes. Finally, the capabilities of Telemac-2D were tested against the experimental data for various turbulence models. The Large Eddy Simulation turbulence model highlighted some unsteady flow patterns that were observed during experiments, while satisfactorily predicting the lateral velocity and boundary shear stress distributions.

To determine whether an artificial reef installation is feasible, there must be a thorough characterization of the habitat. An understanding of both small-scale and large-scale environmental processes is needed to determine factors that potentially will influence the reef. Large-scale processes include coastal circulation, wave climate, and sediment dynamics that take place over spatial scales of tens to hundreds of kilometers in the region of the reef. Small-scale processes include the physical characteristics in the immediate vicinity of the reef - the local current, wave and tide characteristics, temperature, salinity, and suspended and bottom sediments at a proposed reef site. The city of Port Richey, Florida, was considering installing an artificial reef of porcelain modules near Durney Key, a dredge spoil island just offshore. To assist in determining the feasibility of this proposal, I pursued three objectives: a) to characterize the oceanographic setting of Durney Key, including hydrodynamics, water quality and invertebrate biota; b) to investigate the potential for successful coral recruitment and growth in Durney Key waters; and c) to determine if porcelain is a suitable substrate for settlement of the larvae of coral species present in west central Florida. An array of Acoustic Doppler Current Profilers (ADCPs) were used to measure water velocity, water stage and temperature around Durney Key. ADCP data showed currents around Durney Key are tidally dominated with velocities increasing in winter due to frontal passages. Seasonal stage variation ranges from 0.29 m (11.4 in) to 0.64 m (2.1 ft) and seasonal temperature ranged from 10°C and 35°C for winter and summer, respectively. Atmospheric data from the Port Richey COMPS site showed average wind speeds were higher in winter (3.7 m/s or 12.4 ft/s) than summer (3.1 m/s or 10.2 ft/s), corresponding to increased average water velocities. Inorganic nutrients, salinity and pH were measured and compared to data from patch reefs in the Florida Keys to characterize the water quality and determine its suitability for coral recruitment and growth. Compared to Florida Keys patch reef waters, Durney Key water salinity averaged 12 parts per thousand (ppt) lower, pH was more variable with a lower minimum, and total phosphorus was much higher. Ceramic and porcelain recruitment tiles deployed to investigate larval recruitment were colonized by turf, coralline and macroalgae, with barnacles recruiting secondarily. Sediment cores revealed foraminiferal and molluscan assemblages characteristic of productive estuarine conditions. The Durney Key area was deemed not suitable for coral recruitment and growth on an inshore artificial substratum because of temperature extremes, potential for minimal water movement during summer, frequent occurrences of low salinity and pH, and high total organic phosphorus. Faunal studies demonstrated that the dominant recruitment reflects the common coastal/estuarine biota, which does not include reef-building corals.

La crue de décembre 2003, sur le Rhône en aval de Beaucaire (11 500 m3 s1) a eu une ligne d'eau plus élevée de 30 à 60 cm que la crue de référence du mois de Mai 1856 (11 640 m3 s1). Cette élévation a provoqué des inondations par surverse sur la berge gauche du Rhône entre Beaucaire et Arles et l'apparition de brèches en rive droite du Petit Rhône, entraînant des dégâts matériels considérables. Elle peut être interprétée en termes de perte de débitance, due à l'évolution géomorphologique du chenal depuis la fin du XIXe siècle.<br />Pour valider cette hypothèse, cette thèse est construite en trois parties. Dans la première, sont analysés les facteurs de la morphogenèse, à l'échelle du bassin-versant et locales (évolution des apports solides, aménagements...), sur la base d'une synthèse des données d'archives et des travaux déjà publiés. Dans la deuxième partie une analyse 2D de l'évolution de l'occupation du sol, puis 3D de la topographie de la plaine et du chenal depuis 150 ans localise et permet de quantifier les zones d'érosion et de stockage sédimentaire. Ces résultats sont discutés et mis en relation avec les forçages généraux et les contraintes locales. L'analyse des brèches du Petit Rhône pose les bases d'une méthode de détermination des zones les plus sensibles à la rupture. Enfin la troisième partie est axée sur l'évolution des flux solides en transit depuis 150 ans : modélisation et calcul de la charge de fond potentielle mise en mouvement en 1876 et en 2006, estimation des flux de MES en transit et de l'impact des aménagements sur leur piégeage ou leur remobilisation à partir de la calibration des données aDcp (dont la validation est présentée).