A mistura vertical de águas profundas, ricas em nutrientes e de baixas temperaturas, características da Água Central do Atlântico Sul (ACAS), com águas de baixa d;sponibilidade nutricional, baixa biomassa fitoplanctônica e de temperaturas mais elevadas, características da Água Costeira (AC), da região de Ubatuba, foi simulada através da realização de bioensaios. As águas foram incubadas com as populações fitoplanctônicas naturais, sem enriquecimentos nutricionais, sob diferentes níveis de atenuação radiação solar incidente total (100, 30 e 10% de IL) e temperatura igual a da água do mar de superfície. o potencial quimico e biológico dos dois tipos de água (ACAS e AC) e de uma mistura equitativa de ambas, foi avaliado através do monitoramento diário de aspectos quali- quantitativos do fitoplâncton (Clorofila-a, contagem e identificação das células e taxas de produção primária) e do teor de nutrientes dissolvidos no meio, durante o período de incubação. Foram realizadas três etapas experimentais: em Jul/88, Jan/89 e Jul/89 com durações de 8, 15 e 14 dias, respectivamente. A mistura da ACAS com AC apresentou os melhores rendimentos máximos de Clorofila-a e produção primária, sob os níveis de 100 e 30 % de IL. A 10% de IL, a ACAS mostrou- se mais produtiva do que quando misturada à AC e, em termos de Cl-a integral, teve rendimento superior inclusive ao obtido pela Mistura a 100% de IL. A AC apresentou um rendimento menor que as outras duas águas sob os três niveis de luz utilizados. Sob intensidades luminosas mais altas os nutrientes foram rapidamente assimilados causando uma floração de espécies oportunistas (diatomáceas) logo no inicio do periodo de incubação, o que não foi observado sob intensidades luminosas menores. Os resultados ainda indicam que os \"lag-time\" observados no inverno foram significativamente maiores que os do verão. Foi também possivel observar a existência de uma estratificação fisiológica das populações fitoplanctônicas presentes em uma mesma massa d\' água, em função da profundidade, no inverno. Esta estratificação provavelmente deveu-se à diferentes suprimentos nutricionais de origem orgânica que estariam disponiveis apenas para as populações da água de fundo, possivelmente devido a interação da água com o sedimento. Estes resultados demostram a grande importância da água da ACAS como agente fertilizador para as águas oligotróficas da região, permitindo a ocorrência de produção nova. / The vertical mixing of the rich, low temperature, deep South Atlantic Central Water (SACW), with the low nutrient, low phytoplanktonic biomass and hiSh temperature Coastal Water (CW), irom Ubatuba region, was simulated erforming bioassays. The waters were incubated with the authoctonous phytoplankton without any nutrient addition, under ifferent attenuation levels (100, 30 and 10% ) of the total incident solar radiation and at the same temperature as the urface sea water. The chemical and biological potential of each water (SACW and CW), and of an equivalent mixture of them, wa evaluated by means of a daily monitoring of quali and quantitative phytoplankton aspects (Chl-a, cell counting and photosynthetic rates) and of the dissolved nutrient concentrations durins the incubation period. Three series of experiments were performed: Jul/88, Jan/89 and Jul/89, lasting 8, 15 and 14 days espectively. The mixing of SACW and CW presented the best maximum yield oi chlorophyll and photosyntetic rates under 100 and 30% solar radiation. Under 10% SACW alone waa more productive than mixed with CW and, considering integral chlorophyll-a during the whole period. it preaented a higher yield than the one obtained with Mixed Water under 100% oí solar radiation. CW preaented the lowest yield under the experimental light leveI used. Under high light intensi ties nutrients were quickly assimilated inducing a bloom of opportunist species (diatoms) at the begining of the incubation period, which was not observed under low light intensities.(diatoms) at the begining of the incubation period, which was not observed under low light intensities. Results also indicate that the Ias times observed during winter were ignificantIy higher than those during summer. It was possible to observe the existence of a Physiological atratification among phytoplank.tonic populations from the same water mass, as a function of depht, durins winter. This phenomenon was probably due to diatinct nutricional aupply of orsanic origen that would be avaiIabIe to deep populations only, possibly as a consequence of ater/sediment interactiona. These results demonstrate the great importance of SACW as a fertilizer agent to the oligothrophic waters of the region, allowing the occurrence of new production.

A mistura vertical de águas profundas, ricas em nutrientes e de baixas temperaturas, características da Água Central do Atlântico Sul (ACAS), com águas de baixa d;sponibilidade nutricional, baixa biomassa fitoplanctônica e de temperaturas mais elevadas, características da Água Costeira (AC), da região de Ubatuba, foi simulada através da realização de bioensaios. As águas foram incubadas com as populações fitoplanctônicas naturais, sem enriquecimentos nutricionais, sob diferentes níveis de atenuação radiação solar incidente total (100, 30 e 10% de IL) e temperatura igual a da água do mar de superfície. o potencial quimico e biológico dos dois tipos de água (ACAS e AC) e de uma mistura equitativa de ambas, foi avaliado através do monitoramento diário de aspectos quali- quantitativos do fitoplâncton (Clorofila-a, contagem e identificação das células e taxas de produção primária) e do teor de nutrientes dissolvidos no meio, durante o período de incubação. Foram realizadas três etapas experimentais: em Jul/88, Jan/89 e Jul/89 com durações de 8, 15 e 14 dias, respectivamente. A mistura da ACAS com AC apresentou os melhores rendimentos máximos de Clorofila-a e produção primária, sob os níveis de 100 e 30 % de IL. A 10% de IL, a ACAS mostrou- se mais produtiva do que quando misturada à AC e, em termos de Cl-a integral, teve rendimento superior inclusive ao obtido pela Mistura a 100% de IL. A AC apresentou um rendimento menor que as outras duas águas sob os três niveis de luz utilizados. Sob intensidades luminosas mais altas os nutrientes foram rapidamente assimilados causando uma floração de espécies oportunistas (diatomáceas) logo no inicio do periodo de incubação, o que não foi observado sob intensidades luminosas menores. Os resultados ainda indicam que os \"lag-time\" observados no inverno foram significativamente maiores que os do verão. Foi também possivel observar a existência de uma estratificação fisiológica das populações fitoplanctônicas presentes em uma mesma massa d\' água, em função da profundidade, no inverno. Esta estratificação provavelmente deveu-se à diferentes suprimentos nutricionais de origem orgânica que estariam disponiveis apenas para as populações da água de fundo, possivelmente devido a interação da água com o sedimento. Estes resultados demostram a grande importância da água da ACAS como agente fertilizador para as águas oligotróficas da região, permitindo a ocorrência de produção nova. / The vertical mixing of the rich, low temperature, deep South Atlantic Central Water (SACW), with the low nutrient, low phytoplanktonic biomass and hiSh temperature Coastal Water (CW), irom Ubatuba region, was simulated erforming bioassays. The waters were incubated with the authoctonous phytoplankton without any nutrient addition, under ifferent attenuation levels (100, 30 and 10% ) of the total incident solar radiation and at the same temperature as the urface sea water. The chemical and biological potential of each water (SACW and CW), and of an equivalent mixture of them, wa evaluated by means of a daily monitoring of quali and quantitative phytoplankton aspects (Chl-a, cell counting and photosynthetic rates) and of the dissolved nutrient concentrations durins the incubation period. Three series of experiments were performed: Jul/88, Jan/89 and Jul/89, lasting 8, 15 and 14 days espectively. The mixing of SACW and CW presented the best maximum yield oi chlorophyll and photosyntetic rates under 100 and 30% solar radiation. Under 10% SACW alone waa more productive than mixed with CW and, considering integral chlorophyll-a during the whole period. it preaented a higher yield than the one obtained with Mixed Water under 100% oí solar radiation. CW preaented the lowest yield under the experimental light leveI used. Under high light intensi ties nutrients were quickly assimilated inducing a bloom of opportunist species (diatoms) at the begining of the incubation period, which was not observed under low light intensities.(diatoms) at the begining of the incubation period, which was not observed under low light intensities. Results also indicate that the Ias times observed during winter were ignificantIy higher than those during summer. It was possible to observe the existence of a Physiological atratification among phytoplank.tonic populations from the same water mass, as a function of depht, durins winter. This phenomenon was probably due to diatinct nutricional aupply of orsanic origen that would be avaiIabIe to deep populations only, possibly as a consequence of ater/sediment interactiona. These results demonstrate the great importance of SACW as a fertilizer agent to the oligothrophic waters of the region, allowing the occurrence of new production.

Ocean optical studies have been conducted extensively in open ocean waters but less so in coastal waters where the influence of human population is increasing dramatically. The waters of the Strait of Georgia, British Columbia, Canada, are very important to the rearing of young salmon and herring, and to the fishing industry of British Columbia overall. The oceanography and plankton communities of the Strait have been researched extensively, however the forces behind the frequent occurrence of phytoplankton blooms in these waters still causes debate among researchers. In order to shed some light onto this topic and increase our knowledge of the characteristics of the waters of the Strait of Georgia, optical and bio-physical data were measured in the euphotic waters of the Strait in late spring and early summer of 2006. Hyperspectral optical data were measured for the first time in these waters using in situ optical profilers to collect inherent optical properties and radiometric quantities that were later used to derive apparent optical properties. The inherent optical properties included absorption coefficient, spectral beam attenuation coefficient, chromophoric dissolved organic matter absorption coefficient, particulate absorption coefficient, and particulate scattering coefficient. In situ irradiances and radiances were used to derive various diffuse attenuation coefficients. Water masses in the euphotic zone of the Strait of Georgia were then classified into three optical water masses according to their inherent optical properties using a clustering algorithm. OM1 waters were characterized by high and spectrally-invariant particulate scattering due to inorganic particles carried by the Fraser River plume. Absorption and scattering showed some spectral dependence in OM2 waters, with particles and chromophoric dissolved organic matter contributing equally to light absorption. The deepest waters, OM3, were the least influenced by the Fraser River, and the contribution of chromophoric dissolved organic matter to absorption was greater than in OM1 and OM2. A radiative transfer model, Hydrolight, was used to model some of the optical properties that were not collected in situ and then used to assess the magnitude of light available to phytoplankton in the Strait. Based on the minimum light requirements for photosynthesis of two of the main phytoplankton species in the Strait, the analysis presented here showed that there was enough light available for photosynthesis in the photosynthetically-available radiation range for the two phytoplankton species in all three optical water masses.

Les forçages physiques conditionnent la discontinuité dans l'espace et le temps (patchiness) du plancton dans l'océan. La thèse s'est basée sur deux exemples. Le premier concerne le nord-ouest des Sargasses où une série temporelle à du macrozooplankton a été analysée à partir du rétro signal acoustique (Sv) mesuré avec un ADCP 153-KHz. Trois types de tourbillons ont été identifiés: un tourbillon cyclonique productif, la périphérie d'un tourbillon "mode-water", et la périphérie d'un tourbillon anticyclonique. Les valeurs de Sv ont augmenté au cours du passage des tourbillons, avec une hausse plus marquée associée au bord des tourbillons cyclonique et anticyclonique, ce qui suggère une réponse biologique significative aux upwelling localisées dans la zone frontale de ces tourbillons. Dans le deuxième exemple, la distribution spatiale et temporelle du zooplancton a été étudiée au large de la Nouvelle-Calédonie au cours de deux campagnes multidisciplinaires en 2011. La variabilité du zooplancton a été évaluée à l'aide d'échantillonnage au filet ainsi qu'à partir de mesures acoustiques (ADCP embarqué, échosondeur scientifique et TAPS). Des amplitudes plus élevées de la migration verticale nycthémérale (DVM) du zooplancton étaient associées à une plus grande abondance de petit zooplancton et aux eaux froides du sud de la zone d'étude, tandis que des amplitudes de DVM plus faibles dans le nord étaient associés à des eaux plus chaudes et à de plus grande abondance des grands organismes. Ces mesures acoustique ont clairement mis en évidence le rôle des forçage physique, notamment des structures à méso-échelle, sur la répartition spatiale et temporelle du zooplancton. / Physical forcing drives the space and time discontinuity (patchiness) of plankton in the ocean. The thesis was focused on the role of these forcing on the zooplankton, studied using both acoustic and traditional methods with net sampling. The study was based on two examples. The first one concerns the northwestern Sargasso Sea where high resolution time-series data on 0-200m macrozooplankton abundance and distribution off Bermuda was estimated from volume backscattering strength (Sv) measured with a 153-Khz ADCP. Three types of eddies were identified: a productive cyclonic eddy, the periphery of a mode water eddy, and the periphery of an anticyclonic eddy. Sv values increased during passage of theses eddies, with a more pronounced increase associated with the edge of the cyclonic and the anticyclonic eddies, suggesting a significant biological response to localized upwelling in the high velocity boundary of these eddies. In the second example, spatial and temporal distribution of zooplankton off New Caledonia was studied during two multidisciplinary cruises in 2011. Zooplankton variability was assessed using net sampling together with acoustic measurements (shipborne ADCP, scientific echosounder and TAPS). Higher amplitudes of diel vertical migration (DVM) of zooplankton were associated with higher abundance of large zooplankton and cold waters to the south of the study area, while lower DVM amplitudes in the north were associated with warmer waters and higher abundance of small organisms. These acoustic measurements clearly evidenced the role of physical forcing, particularly mesoscale features, in shaping zooplankton space and time distribution.

La recherche porte sur les patrons de distribution longitudinale (amont-aval) et transversale (rive nord - rive sud) des communautés de crustacés planctoniques qui ont été analysés le long du fleuve Saint-Laurent entre le lac Saint-François et la zone de transition estuarienne, à deux hydropériodes en mai (crue) et en août (étiage). Les données zooplanctoniques et environnementales ont été récoltées à 52 stations réparties sur 16 transects transversaux en 2006. Au chapitre 1, nous présentons les principaux modèles écosystémiques en rivière, une synthèse des facteurs influençant le zooplancton en rivières et les objectifs et hypothèses de recherche. Au chapitre 2, nous décrivons la structure des communautés de zooplancton dans trois zones biogéographiques du fleuve et 6 habitats longitudinaux, ainsi que les relations entre la structure du zooplancton et la distribution spatiale des masses d’eau et les variables environnementales. Au chapitre 3, nous réalisons une partition de la variation des variables spatiales AEM (basées sur la distribution des masses d’eau) et des variables environnementales pour évaluer quelle part de la variation du zooplancton est expliquée par les processus hydrologiques (variables AEM) et les conditions locales (facteurs environnementaux). Le gradient salinité-conductivité relié à la discontinuité fleuve-estuaire a déterminé la distribution à grande échelle du zooplancton. Dans les zones fluviales, la distribution du zooplancton est davantage influencée par la distribution des masses d’eau que par les facteurs environnementaux locaux. La distribution des masses d’eau explique une plus grande partie de la variation dans la distribution du zooplancton en août qu’en mai. / The research aims to determine the distribution patterns of crustacean plankton along the longitudinal (west-east) and transversal (north shore - south shore) axes of the St. Lawrence River between Lake Saint-François and the estuarine transition zone, during two hydroperiods in May (high discharge) and August (low discharge). The zooplankton samples and the environmental data were collected at 52 stations distributed along 16 transversal transects in 2006. In chapter 1, we present the theoretical concepts of river ecosystem models, and a synthesis on the generative processes driving zooplankton spatial patterns in rivers. We also present our research objectives and hypotheses. In chapter 2, we describe spatial patterns of the zooplankton community structure in three biogeographic zones of the St. Lawrence and 6 longitudinal habitats, together with the relationships between zooplankton spatial structure and water masses spatial distribution and environmental characteristics. In chapter 3, we perform a variation partitioning procedure on spatial variables AEM (based on water masses spatial distribution) and environmental variables in order to assess how much of the zooplankton variation is explained by hydrological processes (AEM variables) and local conditions (environmental factors). The salinity-conductivity gradient related to the fluvial-estuary discontinuity determines the large-scale spatial patterns of the crustacean zooplankton. In the fluvial zones, the zooplankton distribution patterns are more influenced by the water masses spatial structure than by local environmental factors. The spatial distribution of the water masses explained more of the spatial structure of zooplankton communities in August than in May.

Les tendances climatiques récentes montrent un réchauffement et un adoucissement des couches de surface dans la région du courant circumpolaire antarctique (ACC).Sur la même période, les vents d'ouest pilotant la circulation de l'océan Austral ont significativement augmentés. Cette augmentation est en partie liée à l'intensification du mode annulaire austral (SAM), principal mode de variabilité atmosphérique au sud de 20°S. Dans cette thèse, on s'intéresse à comprendre les effets de la tendance positive du SAM sur les propriétés des masses d'eau formées dans la région de l'ACC.A cette fin, on met en place une stratégie de simulations régionales couplées océan-glace de mer et forcées par une série de scénarios atmosphériques perturbés. Les scénarios atmosphériques sont construits à partir de réanalyses atmosphériques afin de décrire les différentes composantes (dynamiques et thermodynamiques) des changements liés au SAM.En réponse à l'intensification du SAM, les simulations montrent une forte salinisation de la couche de mélange océanique ainsi que des eaux modales (SAMW) et intermédiaires (AAIW).L'essentiel de ces changements peut être attribué aux composantes dynamiques du SAM. Dans les régions saisonnières englacées, les composantes thermodynamiques du SAM peuvent jouer un rôle important (en particulier en mer d'Amundsen et en mer de Weddell). Les simulations montrent également le rôle clef joué par la glacede mer dans la médiation des changements atmosphériques vers l'océan intérieur. Ces résultats de simulations suggèrent que le SAM ne serait pas le seul pilote des tendances climatiques récentes dans l'océan Austral. / Recent climate trends show a warming and freshening of the surface layers in the region of the Antarctic Circumpolar Current (ACC). Over the same period, the westerlies driving the circulation of the Southern Ocean have significantly increased. This increase is partly due to the intensification of the Southern Annular Mode (SAM), the main mode of atmospheric variability south of 20°S. In this thesis, we are interested in understanding the effects of the positive trend of the SAM onto the properties of water masses formed in the region of the ACC. To do so, we implement a strategy of regional coupled ocean-sea ice simulations forced by a series of atmospheric disturbance scenarios.These scenarios are constructed from atmospheric reanalyses in order to describe the various components (dynamic and thermodynamic) of the changes related to the SAM. In response to the increase of the SAM, the simulations show a significant salinification of the ocean mixed layer and of the mode water (SAMW) and intermediate water (AAIW).Most of these changes can be attributed to the dynamic components of the SAM. In Seasonal Ice Zone, the thermodynamic components of the SAM can play an important part (especially in Amundsen Sea and Weddell Sea). The simulations also show the key role played by sea ice in mediating atmospheric changes toward the interior ocean.These simulation results suggest that SAM is not the only driver of recent climate trends in the Southern Ocean.

La recherche porte sur les patrons de distribution longitudinale (amont-aval) et transversale (rive nord - rive sud) des communautés de crustacés planctoniques qui ont été analysés le long du fleuve Saint-Laurent entre le lac Saint-François et la zone de transition estuarienne, à deux hydropériodes en mai (crue) et en août (étiage). Les données zooplanctoniques et environnementales ont été récoltées à 52 stations réparties sur 16 transects transversaux en 2006. Au chapitre 1, nous présentons les principaux modèles écosystémiques en rivière, une synthèse des facteurs influençant le zooplancton en rivières et les objectifs et hypothèses de recherche. Au chapitre 2, nous décrivons la structure des communautés de zooplancton dans trois zones biogéographiques du fleuve et 6 habitats longitudinaux, ainsi que les relations entre la structure du zooplancton et la distribution spatiale des masses d’eau et les variables environnementales. Au chapitre 3, nous réalisons une partition de la variation des variables spatiales AEM (basées sur la distribution des masses d’eau) et des variables environnementales pour évaluer quelle part de la variation du zooplancton est expliquée par les processus hydrologiques (variables AEM) et les conditions locales (facteurs environnementaux). Le gradient salinité-conductivité relié à la discontinuité fleuve-estuaire a déterminé la distribution à grande échelle du zooplancton. Dans les zones fluviales, la distribution du zooplancton est davantage influencée par la distribution des masses d’eau que par les facteurs environnementaux locaux. La distribution des masses d’eau explique une plus grande partie de la variation dans la distribution du zooplancton en août qu’en mai. / The research aims to determine the distribution patterns of crustacean plankton along the longitudinal (west-east) and transversal (north shore - south shore) axes of the St. Lawrence River between Lake Saint-François and the estuarine transition zone, during two hydroperiods in May (high discharge) and August (low discharge). The zooplankton samples and the environmental data were collected at 52 stations distributed along 16 transversal transects in 2006. In chapter 1, we present the theoretical concepts of river ecosystem models, and a synthesis on the generative processes driving zooplankton spatial patterns in rivers. We also present our research objectives and hypotheses. In chapter 2, we describe spatial patterns of the zooplankton community structure in three biogeographic zones of the St. Lawrence and 6 longitudinal habitats, together with the relationships between zooplankton spatial structure and water masses spatial distribution and environmental characteristics. In chapter 3, we perform a variation partitioning procedure on spatial variables AEM (based on water masses spatial distribution) and environmental variables in order to assess how much of the zooplankton variation is explained by hydrological processes (AEM variables) and local conditions (environmental factors). The salinity-conductivity gradient related to the fluvial-estuary discontinuity determines the large-scale spatial patterns of the crustacean zooplankton. In the fluvial zones, the zooplankton distribution patterns are more influenced by the water masses spatial structure than by local environmental factors. The spatial distribution of the water masses explained more of the spatial structure of zooplankton communities in August than in May.