Com o presente trabalho contribuiu-se para o estudo das composições químicas das estrelas simbióticas do hemisfério sul, muito pouco exploradas na literatura. Apresenta-se um conjunto completo de simbióticas amarelas austrais extraído do catálogo de Belczynski [Belczynski]. Alguns dos objetos analisados não possuem nem sequer dados espectroscópicos na literatura. Obtém-se os dados deste trabalho com o telescópio de 1.6 m do LNA e da base de dados do satélite I.U.E. Calcula-se o avermelhamento a partir das linhas de recombinação do H, aplicando os valores de extinção interestelar obtidos dos espectros no visível aos do U.V. A partir das razões entre as linhas do [OIII] e [NII] e supondo uma temperatura eletrônica de 12 000 K (Nussbaumer [NussbuamerNP]) encontra-se as densidade eletrônicas presentes nas nebulosas dos sistemas simbióticos. Com estes dados, mais os os fluxos das linhas derivam-se as abundâncias químicas das nebulosas dos sistemas simbióticos; C, N, O no U.V. e He, Ar, S, O e N no visível. Comparam-se as abundâncias no visível com as das simbióticas na direção do bojo (Luna [Luna]) e com nebulosas planetárias (Escudero [Escudero]). Nota-se que em geral as simbióticas são mais enriquecidas em N e He do que as planetárias isto ocorre provavelmente porque as progenitoras das estrelas simbióticas são mais massivas do que a das planetárias. No entanto, para elementos como O, Ar e S encontram-se abundâncias muito próximas entre simbióticas e planetárias. Comparam-se também, as abundâncias das simbióticas amarelas desta amostra com a de planetárias do disco extraídas do trabalho de Pottasch [Pottasch84] , cefeidas de Luck e Lambert [Luck], abundâncias das gigantes G,K e M obtidas a partir de Lambert e Ries[Lambert], as anãs G e K de Reddy et al [Reddy], as gigantes M de Smith e Lambert[Smith90], abundâncias das estrelas Ba extraídas de Smith [Smith84], as estrelas mild Ba dos tipos espectrais G8 a K3 de Berdyugina [Berdyugina] , as early R de Dominy [Dominy], estrelas C de Lambert et al [Lambert86] e por fim as estrelas M e S (MS) de Smith & Lambert [Smith90]. Pode-se distinguir dois grupos de simbióticas amarelas a partir dos diagramas C/N-O/N. Um grupo apresenta produtos do ciclo CN e situa-se próximo à curva de baixa metalicidade e metalicidade solar. O outro grupo, encontra-se próximo da curva C/O=1, que consiste de objetos enriquecidos em carbono (Schmid & Nussbaumer[Nussbaumer01]). As estrelas simbióticas amarelas enriquecidas em C não estão univocamente associadas as estrelas Ba ou early R. Estes dois grupos representam as simbióticas amarelas tipo s e d' respectivamente. Por fim, conclui-se que os sistemas simbióticos amarelos analisados neste trabalho confirmam o modelo de que seriam estrelas AGBs iluminadas por alguma fonte quente de radiação. / The present work is a contribution to the study of chemical composition of southern symbiotic stars, scarcely studied in literature. We present a complete set of yellow southern symbiotic stars extracted from Belczynski. Some of the objects analyzed had no spectroscopic data in literature. The data were obtained using 1.6m telescope in LNA, Brazil and the IUE satelite database. The reddening was calculated from Hydrogen recombination lines. From the ratio fluxes of the lines of [OIII] and [NII] and a hypothetical electronic temperature of 12 000K (Nussbaumer) we estimated the eletronic density of the nebulae present in the symbiotic system. With this data plus the fluxes of lines observed we obtained the chemical abundances in symbiotic nebulae; C,N,O in U.V. and He, Ar, S, O and N in visible. The abundances of the yellow symbiotic stars were compared to planetary disc nebulae extracted from Pottasch, cefeids form Luck & Lambert, G, K and M giant abundances from Lambert & Ries, G and K dwarfs from Reddy et. al., M giants from Smith & Lambert, Ba star abundances from Smith, mild Ba stars type G8 and K3 from Berdygina, early R from Dominy, C stars form Lambert et. al. and M and S (MS)stars from Smith & Lambert. We can distinguish two types of yellow symbiotic groups. One group presents CN cycle products and is situated near the low metalicity and solar metalicity curve. The other group is found near the C/O=1 curve that is made of rich carbon objects (Schmid & Nussbaumer).The yellow symbiotic stars enriched in carbon are not univically asociated with Ba or early R stars. These two groups represent respectively the yellow s and d' symbiotics. The yellow symbiotic stars analyzed in this work confirm the model in which they would be AGB stars iluminated by some hot source radiation.

Les modifications environnementales qui affectent aujourd'hui les milieux marins recouvrent des problématiques scientifiques et sociétales majeures, d'autant que ces changements devraient s'accélérer au cours du 21ème siècle. Comprendre et anticiper la réponse de la biodiversité marine à ces changements représente un enjeu scientifique d'actualité. Les approches biogéographiques et macroécologiques constituent un cadre scientifique dans lequel il est possible d'étudier, de décrire, et de comprendre les motifs de distribution des espèces à large échelle et d'estimer leur évolution possible face aux changements environnementaux. C'est notamment le cas dans l'océan Austral où les effets du changement climatique se font déjà sentir et où les modifications environnementales associées pourraient avoir des effets profonds sur la structure et le fonctionnement des écosystèmes. Malgré de récents efforts d'échantillonnage, nos connaissances sur la distribution des espèces dans l’océan Austral comptent encore de nombreuses lacunes attribuables au caractère récent des découvertes, à l'isolement et à l'éloignement de cet océan d'accès difficiles. Dans ce contexte, les objectifs de cette thèse consistaient à mieux comprendre les motifs de distribution d'espèces à l’échelle de l’océan Austral, à mettre en évidence les facteurs qui en sont à l’origine et enfin, à évaluer l’impact du changement climatique sur leur distribution. Pour cela,différents types de modèles de niche écologique (MNE) ont été employés. Les échinides (oursins), organismes communs des communautés benthiques de l’océan Austral ont servi de modèle d'étude pour ce travail. Afin de générer des MNE, notamment de type corrélatif, une base de données d’occurrence des espèces d'échinide a été actualisée. L’effort d’échantillonnage a ainsi pu être cartographié et quantifié pour l'ensemble de l'océan Austral ;il s'est révélé très hétérogène, principalement concentré aux abords des zones peu profondes et des bases scientifiques. Cela peut générer des biais dans la qualité et la performance prédictive des MNE ainsi que dans les projections spatiales associées. La robustesse des MNE corrélatifs a donc été testée au regard de l’effort d’échantillonnage mais aussi en tenant compte de la taille des niches écologiques des espèces étudiées ainsi que des contraintes biogéographiques existantes. Cette approche a permis de souligner l’importance de certains facteurs abiotiques pour expliquer la distribution des espèces à large échelle. Il apparaît aussi qu’une meilleure qualité d'échantillonnage génère des MNE plusrobustes mais que les résultats sont fortement dépendants de la taille des niches écologiques et de la présence de barrières biogéographiques.Ces MNE individuels réalisés pour de nombreuses espèces ont été combinés entre eux et ont permis de définir dix écorégions à l'échelle de l'océan Austral qui se distinguent par leur composition faunique et leurs caractéristiques environnementales. Les résultats montrent une forte individualisation des faunes antarctiques par rapport aux régions subantarctiques ainsi que l'existence de liens fauniques entre l’Amérique du Sud et les îles subantarctiques d'une part, ainsi qu’entre la nouvelle Zélande et la mer de Ross de l'autre. Ils soulignent également l’importance de facteurs environnementaux comme la température de fond, la profondeur et la géomorphologie pour expliquer les motifs de distribution des espèces. Enfin, des modèles prédictifs futurs ont été produits sur la base du scénario RCP 8.5 du GIEC. Ils montrent que les régions subantarctiques pourraient être particulièrement impactées par les changements environnementaux y compris au sein du réseau d’Aires Marines Protégées (AMP) mis en place dans l’océan Austral. Les MNE corrélatifs ont fait l’objet de critiques récurrentes dans la littérature scientifique du fait de leur incapacité à prendre en compte les dynamiques biologiques liant espèce et environnement, et de leurs limites pour l'extrapolation des données et la production de projections futures. Des MNE de types mécanistiques reposant sur l'approche des Dynamic Energy Budget ont donc été produits pour l'espèce Sterechinus neumayeri (Meissner, 1900) grâce aux nombreuses connaissances acquises sur le développement et la croissance de l'espèce. La comparaison entre MNE corrélatifs et mécanistiques a permis d’apprécier leur complémentarité et de proposer des projections robustes pour la période actuelle. En revanche, les projections futures ont montré de fortes divergences entre modèles, soulignant la nécessité d'utiliser plusieurs approches de modélisation pour mieux comprendre la distribution des espèces à large échelle et évaluer l’impact du changement climatique sur la biodiversité marine de l’océan Austral. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

En los últimos 150 años la humanidad incrementó la emisión de CO2, acelerando el calentamiento atmosférico global. La retención de carbono orgánico en los suelos (COS) mitiga dicho efecto y contribuye a mejorar la calidad del recurso. Los factores que regulan el COS pueden analizarse desde la perspectiva pedológica utilizando la ecuación de estado, que postula que modificaciones en los factores formadores (FF) producirán variaciones en los procesos pedogenéticos (PP) y cambios en las propiedades de los suelos. Los objetivos de la presente tesis fueron: i) Cuantificar los niveles de COS en regiones geográficas homogéneas y establecer su variación a través del paisaje; ii) Evaluar efectos por cambio en la condición climática sobre COS en suelos de granulométrica homogénea y similar relieve; iii) Establecer efectos sobre COS por cambios en los materiales parentales (MP) en condiciones análogas de relieve y clima; iiii) Determinar la acción antrópica por diferentes usos de la tierra e intensidades de uso agrícola. El área de estudio se ubicó en la Pampa Austral, abarcando 110 perfiles en los que se evaluaron 15 variables de sitio, morfológicas, físicas, químicas, biológicas y taxonómicas. Los resultados indicaron que el relieve fue el FF de mayor influencia sobre COS y que la incidencia del resto de los FF varió en función del mismo. Las llanuras de inundación presentaron los más altos contenidos de COS, superando a los valles interserranos y paleocauces, seguidos de planos normales o cóncavos, lomadas y laderas. El análisis jerárquico permitió una mayor comprensión de los FF, PP y mejor predicción del COS. El clima ejerce una acción positiva afectada por el relieve y el MP. En suelos de sedimentos loéssicos y en planos normales la precipitación media anual y la profundidad efectiva en conjunto explicaron un 49 % de la variabilidad del COS (P <0,01). Los MP ejercieron influencia regional sobre COS (r= 0,28, P <0,05, N= 110), aún con la interferencia de otros FF. Los sedimentos aluviales presentaron elevados niveles de COS (171 Mg ha-1), seguido por los sedimentos loéssicos (108 Mg ha-1) y sedimentos eólicos recientes (81 Mg ha-1). El uso produjo cambios en el carbono de 0-25 cm y en el carbono orgánico de 0-1 m. El uso forestal mostró los más altos contenidos de CO0-25 en todos los materiales parentales. La intensidad del uso impactó de manera diferencial sobre el COS en función de la granulometría. Bajo agricultura extractiva los suelos de texturas gruesas presentaron mermas del 60 % en CO. La inclusión de siembra directa y pasturas puede lograr retenciones de 0,7 Mg ha-1 año-1. Se ha demostrado que el relieve es el FF que regula los niveles de COS de la región, modificando el balance de los PP. COS mostró respuesta a la intensidad de la melanización. Los PP modificaron su relación en función de la profundidad efectiva: los suelos someros presentaron melanización intensa, mientras que los suelos profundos redujeron la misma a favor de la iluviación o la alcalinización. La clasificación taxonómica a nivel de familia reflejó claramente los principales FF y PP que ocurren en la Pampa Austral. Las taxas de suelos segregadas y los contenidos de carbono orgánico presentaron una fuerte asociación, lográndose a partir de ellas una mayor certidumbre en la explicación de la variabilidad del COS. Palabras claves: Carbono orgánico del suelo, factores formadores, procesos pedogenéticos, usos del suelo, retención de carbono, Pampa Austral. / Human activity increased CO2 emissions in the last 150 years, accelerating global atmospheric warming. Soil organic carbon storage (SOC) mitigates warming and helps to improving soil quality. Factors that regulate SOC can be analyzed from the pedological approach using the equation of state factors, says changes in the soil forming factors (FF) and their interactions produce variations in pedogenic processes (PP) and changes in soil properties. The objectives of this thesis were: i) measure SOC levels in homogeneous geographic region and analyzing variability across landscape; ii) measure effects of change climatic condition of SOC in soils with similar parent material (PM) and relief; iii) quantify effects on SOC for changes in PM to similar conditions of relief and climate; iiii) determine antropic effects by different land uses and management practices. The study area was located in Austral Pampa, using 110 soil profiles in which 15 site, morphological, physical, chemical, biological and taxonomic variables were evaluated. Results indicated that relief was the most influential FF on SOC, and the incidence of the remaining FF varied according to the same. Flood-plains showed the highest SOC level, followed by saw-valleys and paleo-valleys, normal flats, concave flats, hills and slopes. Hierarchical analysis showed greater understanding of the FF, PP and better prediction of SOC. The climate has a positive effect modified by relief and PM. In soils of loess sediments located in normal flats annual average rainfall and the effective depth explained 49% of the SOC variability (P <0.01). PM presented a regional effect on COS (r = 0.28, P <0.05, N= 110), despite the interference from other FF. Alluvial sediments showed high COS levels (171 Mg ha-1) followed by loess sediments (108 Mg ha-1) and recent aeolian sediments (81 Mg ha-1). Land use produced changes in 0-25 cm and 0-1 m organic carbon. Forest use showed the highest organic carbon content in 0-25 cm on all parent materials. Tillage systems and management practices impacted differently on the SOC in relation to soil texture. Intensive farming in coarse soils showed declines of 60% in CO. No-tillage and pasture showed retention rates of 0.7 Mg ha-1 yr-1. Relief is the main FF regulating COS levels in the region and the balance of the PP, and responded to intensity of melanization. PP changed their relationship as a function of effective depth: shallow soils showed intense melanization, whereas deep soils reduced melanization in favor of illuviation or alkalinization. Soil Taxonomy family level reflected clearly the main FF and PP occurring in the Austral Pampa. Soil taxas segregated and organic carbon contents showed a strong association, improving the explanation of SOC variability. Keywords: Soil organic carbon, soil forming factors, pedogenetic processes, land use, carbon retention, Austral Pampa.

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.

Neste trabalho é apresentado um estudo sobre a estrutura vertical e massas d\'água presentes na região oeste e norte da Península Antártica. Foram utilizados dados de temperatura, salinidade e pressão (profundidade) coletados por plataformas de coleta de dados (PCDs) fixadas em elefantes-marinhos do sul (EMS) pelo Projeto MEOP-BR, coordenado pela Profª Dra Mônica M. C. Muelbert, no período de fevereiro a novembro de 2008. Estes dados são transmitidos via sistema de satélites ARGOS a uma taxa de 2.91+/-0.25 vezes ao dia, distância média entre cada perfil coletado é de 14.43 +/- 12.28 km resultando em uma resolução espacial de 41.61 km/dia. Estes dados permitiram uma descrição detalhada da estrutura vertical e identificação de massas d\'água durante diferentes meses do ano de 2008. São comparados perfis verticais em diferentes estações do ano em regiões de plataformas de gelo marinho, do Estreito de Bransfield (EB) e norte da Península Antártica (PA), comparados transectos da porção oeste da PA coletados durante o verão e inverno de 2008 e são apresentados transectos através do Mar da Escócia (ME) nos meses de Setembro a Outubro de 2008. Os valores de temperatura potencial coletados estiveram na faixa entre -1.89ºC e 2.32ºC, os valores mínimos estão relacionados a áreas de formação de gelo marinho e os máximos a investidas através da Corrente Circumpolar Antártica (CCA) em mar aberto e em direção as Ilhas Georgia (IGS). Os valores de salinidade possuem variações entre 32.36 e 35.03 psu, estes valores resultam de diferentes processos, sendo os extremos relacionados a regiões de derretimento e formação de gelo marinho, respectivamente. Graças à grande área utilizada pelos EMS para forrageio durante o x período analisado, diversas massas d\'água são identificadas através de diagramas -S, são elas: Água Profunda Circumpolar (CDW), Água de Inverno (WW), Água de Plataforma de Baixa Salinidade (LSSW), Água Superficial Antártica (AASW), Água de Plataforma de Alta Salinidade (HSSW), Água Profunda Circumpolar Superior e Inferior (UCDW e LCDW), Água de Plataforma (SW), Água de Plataforma de Gelo (ISW), Água Profunda Cálida (WDW) e Água Profunda Cálida Modificada (MWDW). / To study the termohaline structure and water masses in the north and west sides of Antarctic Peninsula, 10 southern elephant seals (EMS) were equipped with highaccuracy conductivity-temperature-depth satellite-relayed data loggers (CTDSRDLs) by the MEOP-BR Project in beginning of 2008 at Elephant Island. Here, we show that measurements collected by these long-ranging, deep-diving predators allow oceanic vertical structure and water masses of the Southern Ocean to be mapped in regions and at times of year not sampled by other oceanographic instruments. These data are transmitted by the ARGOS satellite system at a rate of 2.91+/-0.25 times per day, mean distance between each profile collected is 14.43+/- 12.28 km, resulting in a spatial resolution of 41.61km/day. Vertical profiles are compared at different seasons in sea ice platforms regions, Bransfield Strait (EB) and northern tip of Antarctic Peninsula (PA). Are compared transects at the western side of the PA collected during summer and winter of 2008 and are presented transects across the Scotia Sea (ME) in the months of September and October of 2008. The collected potential temperature values were in the range from -1.89º C to 2.32ºC, the minimum values are related to areas of sea ice formation and the maximum amounts to dives through the Antarctic Circumpolar Current (ACC) in the open sea and towards the South Georgia Islands. The salinity values have variations between 32.36 and 35.03 psu, these values result from different processes, being related to melting and formation of sea ice. The large region sampled allowed us to identify during the study period several water masses from -S diagrams, they are: Circumpolar Deep Water (CDW), Winter Water (WW), Low Salinity Shelf Water xii (LSSW), Antarctic Surface Water (AASW), High Salinity Shelf Water (HSSW), Upper and Bottom Circumpolar Deep Water (UCDW and LCDW), Shelf Water (SW), Ice Shelf Water (ISW), Warm Deep Water (WDW) and Modified Warm Deep Water (MWDW).

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.

Neste trabalho é apresentado um estudo sobre a estrutura vertical e massas d\'água presentes na região oeste e norte da Península Antártica. Foram utilizados dados de temperatura, salinidade e pressão (profundidade) coletados por plataformas de coleta de dados (PCDs) fixadas em elefantes-marinhos do sul (EMS) pelo Projeto MEOP-BR, coordenado pela Profª Dra Mônica M. C. Muelbert, no período de fevereiro a novembro de 2008. Estes dados são transmitidos via sistema de satélites ARGOS a uma taxa de 2.91+/-0.25 vezes ao dia, distância média entre cada perfil coletado é de 14.43 +/- 12.28 km resultando em uma resolução espacial de 41.61 km/dia. Estes dados permitiram uma descrição detalhada da estrutura vertical e identificação de massas d\'água durante diferentes meses do ano de 2008. São comparados perfis verticais em diferentes estações do ano em regiões de plataformas de gelo marinho, do Estreito de Bransfield (EB) e norte da Península Antártica (PA), comparados transectos da porção oeste da PA coletados durante o verão e inverno de 2008 e são apresentados transectos através do Mar da Escócia (ME) nos meses de Setembro a Outubro de 2008. Os valores de temperatura potencial coletados estiveram na faixa entre -1.89ºC e 2.32ºC, os valores mínimos estão relacionados a áreas de formação de gelo marinho e os máximos a investidas através da Corrente Circumpolar Antártica (CCA) em mar aberto e em direção as Ilhas Georgia (IGS). Os valores de salinidade possuem variações entre 32.36 e 35.03 psu, estes valores resultam de diferentes processos, sendo os extremos relacionados a regiões de derretimento e formação de gelo marinho, respectivamente. Graças à grande área utilizada pelos EMS para forrageio durante o x período analisado, diversas massas d\'água são identificadas através de diagramas -S, são elas: Água Profunda Circumpolar (CDW), Água de Inverno (WW), Água de Plataforma de Baixa Salinidade (LSSW), Água Superficial Antártica (AASW), Água de Plataforma de Alta Salinidade (HSSW), Água Profunda Circumpolar Superior e Inferior (UCDW e LCDW), Água de Plataforma (SW), Água de Plataforma de Gelo (ISW), Água Profunda Cálida (WDW) e Água Profunda Cálida Modificada (MWDW). / To study the termohaline structure and water masses in the north and west sides of Antarctic Peninsula, 10 southern elephant seals (EMS) were equipped with highaccuracy conductivity-temperature-depth satellite-relayed data loggers (CTDSRDLs) by the MEOP-BR Project in beginning of 2008 at Elephant Island. Here, we show that measurements collected by these long-ranging, deep-diving predators allow oceanic vertical structure and water masses of the Southern Ocean to be mapped in regions and at times of year not sampled by other oceanographic instruments. These data are transmitted by the ARGOS satellite system at a rate of 2.91+/-0.25 times per day, mean distance between each profile collected is 14.43+/- 12.28 km, resulting in a spatial resolution of 41.61km/day. Vertical profiles are compared at different seasons in sea ice platforms regions, Bransfield Strait (EB) and northern tip of Antarctic Peninsula (PA). Are compared transects at the western side of the PA collected during summer and winter of 2008 and are presented transects across the Scotia Sea (ME) in the months of September and October of 2008. The collected potential temperature values were in the range from -1.89º C to 2.32ºC, the minimum values are related to areas of sea ice formation and the maximum amounts to dives through the Antarctic Circumpolar Current (ACC) in the open sea and towards the South Georgia Islands. The salinity values have variations between 32.36 and 35.03 psu, these values result from different processes, being related to melting and formation of sea ice. The large region sampled allowed us to identify during the study period several water masses from -S diagrams, they are: Circumpolar Deep Water (CDW), Winter Water (WW), Low Salinity Shelf Water xii (LSSW), Antarctic Surface Water (AASW), High Salinity Shelf Water (HSSW), Upper and Bottom Circumpolar Deep Water (UCDW and LCDW), Shelf Water (SW), Ice Shelf Water (ISW), Warm Deep Water (WDW) and Modified Warm Deep Water (MWDW).

Du fait de l’isolement géographique de l’océan austral et des conditions météorologiques qui y règnent, la collecte de données océanographiques par les moyens conventionnels est particulièrement couteuse dans cette région du globe. Pour pallier à ces difficultés, l’utilisation d’enregistreurs électroniques embarqués sur des prédateurs marins, et notamment sur les éléphants de mer austraux, s’est révélée être une approche intéressante. Les femelles éléphants de mer s’alimentent en grande partie de petits poissons méso-pélagiques bioluminescents, les myctophidés. Leur forte abondance et leur comportement de migration nycthémérale confèrent à ces organismes un rôle écologique de première importance dans l’océan austral. Cependant, la distribution spatiale des proies de l’éléphant de mer, et les processus physiques et biologiques qui influent sur la dynamique de cette distribution sont encore mal connus. Cette thèse se propose d’enquêter sur ces sujets à partir des données à haute fréquence d’échantillonnage collectées par des femelles éléphants de mer. L’analyse du comportement de plongée des femelles éléphants de mer, en relation avec les variations du taux de rencontre de proie dont les données d’accélération permettent d'avoir une estimation, est au cœur des différents travaux développés dans cette thèse. Les résultats obtenus suggèrent notamment, (1) une diminution de l’abondance des proies avec la profondeur ainsi qu’une homogénéisation de leur distribution, (2) une distribution en couches de cette ressource, (3) l’intervention de contraintes verticales délimitant l’étendue verticale de ces couches et ainsi capable de moduler leur densité, (4) au sein des couches, une dispersion relativement importante des proies en comparaison de la portée des capacités de perception du prédateur, et enfin (5) un rôle significatif des tourbillons méso-échelle et de leur bordure sur la structuration de la distribution des ressources alimentaires de l’éléphant de mer durant l’été austral. / Because of the remoteness and harsh meteorological conditions of the southern ocean, data sampling is more costly in this area. Use of electronic devices attached to marine predators (Bio-logging), such as southern elephant seals, has emerged as an interesting approach to cope with this problem. Female southern elephant seals primarily feed on small bioluminescent meso-pelagic fishes called myctophids. Because of their large abundance and of their diel vertical migration behaviour, these organisms have a major ecological importance in the southern ocean. However, the spatial distribution of the elephant seals prey, as well as the bio-physical processes affecting the dynamics of this distribution, are still poorly known. This thesis intends to investigate this issue using high sampling frequency bio-logging data collected by female southern elephant seals. This work is based on the analysis of elephant seals diving behaviour in relation to changes in the occurrence of prey encounter events detected from acceleration data. Our results suggest that (1) prey abundance decreases with depth and that their distribution tend to standardize, (2) prey are distributed into layers, (3) vertical constraints could modulate the prey density by acting on the vertical spread of these layers, (4) prey items are well dispersed in comparison to the perception range of elephant seals, and finally (5) that meso-scale eddies, notably their edges, play a structuring role in the prey distribution during the austral summer.

We investigate the silicon (Si) cycle in the Southern Ocean through two isotopic approaches: (1) 30Si-incubation experiments and (2) natural silicon isotopic composition (ä30Si). 30Si-spiked incubation allows to discriminate the short-term (~ 1 day) net Si-uptake flux in bSiO2 production and dissolution. ä30Si of both biogenic silica and dissolved silicon integrates at seasonal/annual scale bSiO2 production or dissolution and mixing.<p>(1) A new mass spectrometer method (HR-SF-ICPMS) has been developed for 30Si-isotopic abundance measurements. This methodology is faster and easier than the previous available methodologies and has the same precision. A complete set of incubation was coupled with parallel 32Si-incubations and the two methodologies give not significantly different bSiO2 production rates. In the Southern Ocean, especially in the southern Antarctic Circumpolar Current, the large silicic acid concentration degrades the sensitivity of the method with Si dissolution fluxes staying generally below the detection limit. In contrast, the 28Si-isotopic dilution was sensitive enough to assess low biogenic silica dissolution rates in silicic acid poor waters of the northern ACC. We show that large accumulation of detrital dissolving biogenic silica after productive period implies really efficient silicon loop with integrated (euphotic layer) dissolution:production ratio equal or larger than 1.<p> (2) We largely expand the silicic acid isotopic data in the open ocean. Relatively simple mass and isotopic balances have been performed in the Antarctic Zone and have allowed to apply for the first time ä30Si in a quantitative way to estimate regional net silica production and quantify source waters fueling bSiO2 productivity. We observe that at the end of the productive period as suggested with 30Si-incubation, large accumulation of detrital biogenic silica in the surface waters increase the D:P ratio and subsequently dampens the bSiO2 production mediated isotopic fractionation with residual biogenic silica carrying heavier ä30Si than expected. Seasonal isotopic evolution is simulated and seems in agreement with our observations. These simulations strongly suggest working with non-zero order equations to fully assess the seasonal expression of the different processes involved: mixing, uptake, dissolution. Si-isotopes are also tracking the origin and fates of the different ACC pools across the Southern Ocean meridional circulation. Moreover during the circumpolar eastward pathway, the bSiO2 dissolution in deep water decreases the corresponding ä30Si values and this imprint is further transmitted via the upper limb of the meridional circulation in the intermediate water masses.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

. Résumé en français: Le modèle climatique régional RegCM3 est utilisépour examiner les effets direct et semi-direct des aérosols sur le climat du sud de l'Afrique pendant l'hiver austral (juin-septembre). La sensibilité des effets simulés aux différents inventaires d'émissions de combustion de biomasse et aux différentes conditions aux limites est evaluer, afin d'estimer l'incertitude associée à ces paramètres. La sensibilité aux conditions aux limites derivées de réanalyses est modeste, mais le forçage radiatif des aérosols varie linéairement en réponse au différents inventaires testées jusqu'à un facteur deux. Le forçage radiatif est toujours négatif, alors que le forçage radiatif au sommet de l'atmosphère est negatif sur la plupart du domaine sauf au-dessus les régions de savane ou le contenu atmosphérique d'aérosols est élevée. Même si la magnitude du forçage radiatif varie, les simulations pour la période présente montrent des impacts climatiques comparables. La température de surface diminue sur la plupart de la région, ce signale qui réduit le biais du modèle sur l'ouest du sous-continent. L'échauffement en altitude est lié à la charge d'aérosols absorbants et cela, en combinaison avec la réduction de température en surface, mène à la stabilisation de la basse atmosphère. Toutefois, dans la moyenne troposphère de la zone équatoriale (entre 8°N et 5°S) cet échauffement à pour résultat un effet de 'pompe à chaleur en altitude'. Cet effet augmente la convection, les précipitations et l'humidité du sol, en accélérant le cycle hydrologique dans cette région. Une étude de la variabilité interannuelle des effets climatiques des aérosols montre que les changements des précipitations en moyenne saisonnière sont plus variables d'un an à l'autre que les changements de température de surface. Par contre, malgré des différences significatives entre les conditions synoptiques, la variabilité synoptique des impacts climatiques des aérosols est faible.