This study Is concerned with the Federal National Council (FNC) in the United Arab Emirates (U.A.E.) under the 1971 Constitution. In selecting the U.A.E. as a case study, a historical and socioeconomic perspective is adopted. The thesis analyses the U.A.E. traditional society and the effect of external factor namely its relation with Britain, and internal factor, viz, the advent of oil wealth, on the power structure in the emirates. Both factors increased the concentration of central power and decreased popular participation. The study provides a theoretical appraisal of the role and functions of the legislature in developing countries. It examines the constitutional functions namely legislative, political and financial. The study suggests new roles that the legislatures performs in Third World countries. The thesis examines the historical development of the U.A.E. constitutional system. Such development ended In 1971 when the emirates adopted a "Provisional Constitution" to the requirements of the rulers. The study explores the 1971 constitution with particular emphasis on the role of the National Council. It analyses the composition, functions, role and constitutional arrangements of the National Council In the U.A.E. The study provides an analysis of the major political and constitutional cases, In which the FNC was a part, in order to examine the practical working of the constitutional provisions in reality. Finally, the thesis attempts to explain the limitations, Imposed on the National Council, present in the existing constitutional framework and suggests some improvements to the status quo. The coimnon ground throughout the thesis is that a constitution with a democratic tendency does not necessarily establish democratic institutions and that it would be more acceptable in a developing country to introduce evolutionary rather than radical changes to its constitutional system. However, the study clarifies the difficulties of concentration of central power in developing countries.

The dominant organic phosphorus compound classes were characterized in marine samples using a new, high recovery method for isolating and concentrating bulk dissolved organic matter (DOM) called combined electrodialysis+reverse osmosis (ED/RO). In contrast to earlier studies which use ultrafiltration (UF) to recover only the high molecular weight DOM, ED/RO is capable of isolating both low molecular weight (LMW) and high molecular weight (HMW) DOM. Samples were collected from a broad range of marine environments: along a transect incorporating coastal and offshore waters off the Southeastern United States, in Effingham Inlet, a Pacific fjord located on Vancouver Island, British Columbia and in the Amundsen Sea, Antarctica. Results from phosphorus nuclear magnetic resonance (31P NMR) analysis reveals a similar abundance of P compound classes between samples, phosphate esters (80-85%), phosphonates (5-10%) and polyphosphates (8-13%). These samples contain significantly higher proportions of polyphosphate P and P esters and lower proportions of phosphonates than measured in previous studies using the UF method. The much higher levels of polyphosphate detected in our samples suggests that polyphosphate is present mainly in the LMW DOM fraction. Polyphosphates in DOM may be present as (or derived from) dissolved nucleotides or organismal polyphosphate bodies, or both. Low molecular weight P esters are likely composed of phosphoamino acids and small carbohydrates, like simple sugar phosphates and/or dissolved nucleotides. Phosphonates in DOM are more prevalent as HMW phosphonate compounds, which suggests that LMW phosphonates are more readily utilized in marine ecosystems. Overall, the investigation of DOM across a size spectrum that includes both the HMW and the LMW fractions reveals a new picture of phosphorus distribution, cycling and bioavailability.

Gravity waves have a significant dynamic effect in the mesosphere. In particular, they drive the mesospheric circulation and are the reason that the summer polar mesosphere is cooler than the winter polar mesosphere. This thesis examines whether the effects of gravity waves are largely determined by filtering effects which allow only gravity waves with certain properties to propagate into the atmosphere. The filtering of gravity waves above Scott Base, Antarctica is examined using a radiosonde derived gravity wave source function, an MF-radar derived mesospheric gravity wave climatology, and a model derived filtering function. Least squares fitting of the source function and filtering function to the observed mesospheric gravity wave climatology allows us to determine which gravity wave phase velocities and propagation direction are likely to be present in the mesosphere and the relative importance of filtering and sources in this region. It is concluded the blocking of eastward gravity waves is important in winter and westward waves in summer.

Submitted by GABRIELLE VIEIRA null (gabriellevieir@gmail.com) on 2018-04-05T12:53:30Z No. of bitstreams: 1 Metabólitos secundários de fungos da Antártica com ação antimicrobiana em Xanthomonas spp.pdf: 8795008 bytes, checksum: 0df6b298004d2d27c6a56a8a8367648b (MD5) / Approved for entry into archive by Adriana Aparecida Puerta null (dripuerta@rc.unesp.br) on 2018-04-05T14:02:49Z (GMT) No. of bitstreams: 1 vieira_g_me_rcla.pdf: 8781866 bytes, checksum: e535d140907c0db6ece0255e817ca841 (MD5) / Made available in DSpace on 2018-04-05T14:02:49Z (GMT). No. of bitstreams: 1 vieira_g_me_rcla.pdf: 8781866 bytes, checksum: e535d140907c0db6ece0255e817ca841 (MD5) Previous issue date: 2018-02-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / As bactérias do gênero Xanthomonas afetam culturas agrícolas de grande importância econômica no Brasil. O controle destas doenças realizado pela utilização de produtos químicos, entre outras práticas, causa impactos negativos na saúde e ao meio ambiente. Isso torna a busca de alternativas sustentáveis de combate a estas doenças cada vez mais importante. Uma possível alternativa aos produtos químicos que tem despertado grande interesse é a aplicação de metabólitos secundários. Suspeita-se que fungos que vivem em ambientes extremos como a Antártica podem produzir metabólitos secundários ainda desconhecidos. Dessa maneira, este projeto teve como objetivo principal investigar a potencial atividade de metabólitos secundários produzidos por 33 fungos isolados do solo contra três espécies de Xanthomonas economicamente importantes para a agricultura do país. Para tanto, foram utilizados fungos coletados em solo em expedição à Antártica (2013) no âmbito do INCT Criosfera, que estão preservados junto à Central de Recursos Microbianos da UNESP. Os extratos (n=66) foram testados contra Xanthomonas patogênicas das culturas de tomate (Xanthomonas euvesicatoria), frutas cítricas (Xanthomonas citri subsp. citri) e maracujá (Xanthomonas axonopodis pv. passiflorae). Do total de extratos brutos submetidos a bioensaio contra os fitopatógenos, 18 (27,27%) apresentaram taxa de inibição ≥ 90%. Os extratos com potencial inibitório tiveram origem em fungos identificados por sequenciamento da região ITS4 e ITS5 como pertencentes ao filo Ascomycota, gênero Pseudogymnoascus. Alguns extratos ativos foram purificados utilizando diversas técnicas cromatográficas por fracionamento bioguiado como cromatografia por exclusão molecular, cromatografia em coluna em fase normal, cromatografia em coluna de fase reversa e cromatografia líquida de alta eficiência por interação hidrofílica. As frações obtidas foram testadas frente à Xanthomonas citri subsp. citri. Duas frações, obtidas por cromatografia líquida de alta eficiência, C2F2 e C2F5 apresentaram atividade inibitória contra o fitopatógeno. / Bacteria of the genus Xanthomonas affect agricultural crops of great economic importance in Brazil. Control of these diseases is made by the use of chemicals, among other practices, that causes negative impacts on human health and the environment. This makes the search for sustainable alternatives to combat these diseases increasingly important. A possible alternative to chemicals that have aroused great interest is the application of secondary metabolites. It is suspected that fungi living in extreme environments such as Antarctica may produce secondary metabolites as of yet unknown. Therefore this study had as main objective investigate the potential activity of secondary metabolites produced by 33 fungi isolated from the soil against three economically important Xanthomonas species. For this purpose fungi previously collected in the Antarctic expedition (2013) under the INCOS Criosfera and preserved at the Microbial Resource Center of UNESP were utillized. The extracts produced by the 33 isolates (n = 66) were tested against pathogenic Xanthomonas of tomato crops: Xanthomonas euvesicatoria; citrus: Xanthomonas citri subsp. citri; and of passion fruit culture, Xanthomonas axonopodis pv. passiflorae. From the total of extracts submitted to bioassay against phytopathogens, 18 (27.27%) presented inhibition rate ≥ 90%. The extracts with inhibitory potential were produced by fungi identified through sequencing of the ITS4 and ITS5 regions as belonging to the Ascomycota phylum, genus Pseudogymnoascus. Some active extracts were purified using chromatography techniques by bioguided fractionation such as solid phase chromatography by molecular exclusion, normal phase column chromatography, reverse phase column chromatography, and high performance liquid chromatography by hydrophilic interaction . The fractions obtained by cromatography were tested for antibacterial activity in Xanthomonas citri subsp. citri. Two fractions, obtained by high performance liquid chromatography, C2F2 and C2F5, showed inhibitory activity against the phytopathogen. / FAPESP: 2015/20629-6.

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Le bilan de masse en surface de l’Antarctique (noté BMS ; résultante de l’équilibre entres les termes d’accumulation et d’ablation) contribue directement aux variations du niveau moyen des mers. Dans le contexte du changement climatique, sa détermination par les modèles atmosphériques est nécessaire pour affiner son estimation présente et future.Les vents violents en périphérie de l’Antarctique de l’Est sont responsables d’un entraînement aérodynamique de la neige en surface qui influence de façon significative le BMS. Le transport de neige par le vent est également à l’origine du développement de formes d’érosion éolienne orientées parallèlement au vent moyen au moment de leur formation et dont la distribution spatiale est un déterminant majeur de la rugosité de surface. Ces éléments de rugosité exercent en retour un effet d’obstacle à l’écoulement qui affecte directement le champ de vent en surface et, par extension, le transport éolien de la neige.Les travaux présentés dans cette thèse portent sur l’observation et la modélisation numérique de l’érosion éolienne de la neige au niveau d’une région côtière de l’Antarctique de l’Est, la Terre Adélie. Dans un premier temps, le modèle atmosphérique régional MAR, qui contient une représentation détaillée des processus de transport éolien, est mis en œuvre à une résolution spatiale de 5 km sur un domaine couvrant la Terre Adélie et comparé sur un mois d’été à des observations météorologiques incluant des mesures continues du vent et du flux éolien massique de neige aérotransportée. Il est montré que les flux éoliens de neige produits par le MAR sont hautement sensibles à la paramétrisation de la rugosité de surface, et qu’une calibration unique de ce paramètre ne permet pas de simuler avec une qualité équivalente le champ de vent en deux points de mesure distants d’à peine 100 km. À partir des observations, les interactions rugosité-érosion sont ensuite étudiées à l’échelle d’évènements individuels d’érosion éolienne. Il est mis en évidence i) que l’effet d’obstacle généré par les formes d’érosion éolienne a un impact inhibiteur sur le flux éolien de neige et ii) que cet effet d’obstacle peut être fortement diminué par l’aptitude des formes d’érosion éolienne à se réorienter parallèlement au vent dominant pendant un événement de transport. L’examen des observations sur une année révèle que ce processus d’ajustement aérodynamique est sujet à des variations temporelles majoritairement reliées à l’historique de la température. Enfin, on montre qu’une reconfiguration du modèle comprenant notamment l’introduction d’une dépendance à la température dans la paramétrisation de la rugosité de surface améliore considérablement la représentation des flux éoliens de neige par le MAR sur l’année considérée. Ces résultats suggèrent qu’une distribution spatiale et temporelle de la rugosité de surface doit être prise en compte dans les modèles atmosphériques pour une simulation réaliste du transport éolien de la neige à l’échelle de l’Antarctique. / The Antarctic ice sheet surface mass balance (SMB; the result of the balance between accumulation and ablation terms) has a direct influence on variations in the global mean sea level. In the context of climate change, atmospheric models are needed to improve its current and future estimation.Intense surface winds over the coastal slopes of East Antarctica are responsible for aerodynamic entrainment of snow at the surface, which has a significant influence on the BMS. Transport of snow by the wind also produces aeolian erosion features aligned parallel to the prevailing winds at the time of their formation. The spatial distribution of these features is a major determinant of surface roughness. On the other hand, surface roughness is an obstacle to flow and directly affects the surface wind field and, by extension, aeolian snow transport.The work presented here is based on observations and numerical modeling of aeolian snow erosion in a coastal stretch of Adélie Land, East Antarctica. First, the regional atmospheric model MAR, which includes a detailed representation of aeolian transport processes, was run at a spatial resolution of 5 km over a zone including Adélie Land and model results were compared with meteorological observations made over one month in summer, including continuous measurements of the wind and the aeolian snow mass flux. Aeolian snow mass fluxes modeled by MAR were highly sensitive to parameterization of surface roughness, and a single calibration of this parameter was not enough to simulate the surface wind field at two measurement points located only 100 km apart with the same accuracy. Consequently, roughness-erosion interactions were analyzed at the scale of individual aeolian erosion events using observations. The results of this analysis underlined that (i) the barrier effect generated by aeolian erosion features had an inhibiting impact on the aeolian snow mass flux and (ii) that the barrier effect can be strongly reduced by the ability of aeolian erosion features to realign with the dominant wind during a transport event. Examination of observations made over a period of one year revealed that this adjustment process is prone to temporal variations mainly linked to past temperatures. Finally, we showed that reconfiguring the model, including introducing temperature dependence in the parameterization of surface roughness considerably improved the representation of aeolian snow mass fluxes by the MAR model for the year concerned. These results suggest that spatial and temporal distribution of surface roughness should be included in atmospheric models for realistic simulations of aeolian snow transport over Antarctica.

Esta tese aborda a definição de um projeto estratégico-científico brasileiro para a Antártida, a partir da análise da evolução da geopolítica do Sistema do Tratado Antártico (STA). A questão antártica, conforme esta tese, se fundamenta em dois pressupostos teóricos antagônicos das relações internacionais, o realismo e o liberalismo. As premissas de cooperação científica e de uso pacífico da região, estabelecidos no Tratado da Antártida (1959), determinaram a discussão do objeto de estudo a partir de uma epistemologia liberal. A geopolítica antártica, neste início do século XXI, pende para uma dialética científico-ambiental, em detrimento da dimensão econômico–territorialista que dominou o discurso para a região austral até o emblemático ano de 1991, quando ocorreu a ratificação do Protocolo sobre Proteção Ambiental do Tratado da Antártida (Protocolo de Madri). Se o século XX foi marcado pelo advento da ciência antártica, representado pelo Ano Geofísico Internacional (1957 - 1958), o presente século se caracteriza, até o momento, como aquele em que essa ciência antártica deverá construir sua própria agenda. Os Estados-signatários, cada vez mais, reconhecem o peso político de uma ciência antártica de excelência dentro do STA. Com a instituição do Programa Antártico Brasileiro (PROANTAR), em 1982, o país passou a defender seus substanciais interesses naquela região, que, em um primeiro momento, estavam subordinados às contingências da Guerra Fria e ao Projeto do Brasil-potência. Todavia, a invocação subjetiva de tais interesses não permitiu que se delimitasse a sua real amplitude. Esse posicionamento geopolítico em relação à Antártida começou a ser referenciado a partir de 2011, quando a questão antártica, através da elaboração de um Planejamento Estratégico para o PROANTAR (2012 - 2022), passou a assumir uma relativa importância estratégica para o país; em outras palavras, o programa aproximou-se de um projeto de Estado. No referido planejamento encontram-se as diretrizes que deverão garantir ao Brasil um status político relevante dentro do STA, o que implica numa participação efetiva do país nas decisões sobre o destino daquela região. A diretriz principal desse processo é a inserção do país no seleto grupo de Estados-signatários que desenvolve pesquisas de ponta na Antártida. Ao Entender a importância estratégico-geopolítica da Antártida para o Brasil, e o protagonismo da ciência na política do STA, esta tese propõe novos desafios e paradigmas à ciência antártica brasileira, apoiando o atual Planejamento Estratégico para o PROANTAR (2012 - 2022) e o mais recente Plano de Ação para a Ciência Antártica (2013 - 2018). Assim, analisar o PROANTAR a partir da definição de um projeto estratégico-científico, e suas repercussões geopolíticas, é o objetivo maior desta tese, implicando nas seguintes metas: uma análise sobre a geopolítica antártica, o que determinou uma discussão preliminar sobre os pressupostos geopolíticos do Tratado e da ciência antártica, a partir de uma perspectiva histórica; uma análise sobre as dimensões da geopolítica da região no limiar do século XXI, identificando o ano de 1991 (ratificação do Protocolo de Madri) como o momento de inflexão do STA, no qual a dimensão científico-ambiental começou a adquirir maior relevância geopolítica; uma análise sobre a questão antártica no pensamento geopolítico brasileiro, que permitiu discorrer sobre a construção de um possível imaginário territorialista antártico, assim como a sua repercussão na dimensão científica do PROANTAR. Por fim, se analisa os novos desafios à ciência antártica brasileira no século XXI: a expansão geográfica das pesquisas do PROANTAR naquele continente, em especial as investigações no interior do manto de gelo antártico, que quebra o paradigma de uma ciência periférica, historicamente restrita à região da Península Antártica; e a instituição de uma política capaz de garantir a qualidade da produção científica, através de um adequado apoio logístico-financeiro. Vencer tais desafios é de importância fundamental para a inclusão da pesquisa antártica brasileira nas chamadas fronteiras emergentes da ciência. Todavia, à medida que se analisa as ações político-científicas, convergentes à definição de um projeto estratégico brasileiro para a Antártida, que vêm sendo implementadas desde o início deste século, mais nítida se tornam as contradições e os obstáculos à definição de tal projeto: os entraves burocráticos e a volatilidade das ações políticas, que, somados a falta de reconhecimento da importância (geo)política de uma ciência antártica de vanguarda, em particular por grande parte dos pesquisadores que atuam no PROANTAR, impedem a instituição de uma política científica e a definição de um projeto estratégico-científico para a região. / This thesis addresses the definition of a Brazilian strategic-scientific project for Antarctica from the analysis of the Antarctic Treaty System (ATS) geopolitical evolution. The Antarctic question, as discussed in this thesis, is based in two antagonistic theoretical premises taken from the foreign relations (realism and liberalism). The premises of scientific collaboration and the pacific use of the region, established in the Antarctic Treaty (1959), determined a discussion of this topic using a liberal epistemology. The Antarctic geopolitics at the beginning of the 21st century leans towards a scientific-environmental dialectics, to the detriment of the economical-territorial dimension that dominated the discourse for the Austral region up to the emblematic year of 1991, when the Protocol on Environmental Protection to the Antarctic Treaty (Madrid Protocol) was ratified. If the 20th century was marked by the arrival of the Antarctic science, represented by the International Geophysical Year (1957-1958), the current century is characterized, so far, as the one in which the Antarctic science should build its own agenda. The Signatory-States increasingly recognize the political weight of an Antarctic science of excellence within the ATS. By establishing the Brazilian Antarctic Program (PROANTAR, from the Portuguese Programa Antártico Brasileiro) in 1982, Brazil started to defend of its substantial interests in the Antarctic region. These interests, at first, were subordinated to the Cold War contingencies and the Brazil-potency Project. However, the subjective invocation of such interests did not allow the delimitation of its real extent. This geopolitical positioning in relation to Antarctica was first mentioned in 2011 when the Antarctic question, through the preparation of a Strategic Planning for PROANTAR (2012 - 2022), acquired a relative strategic importance for the country. In other words, the program became closer to a project of State. This plan contains directives that shall grant a relevant political status to Brazil within the ATS, which implies the effective participation of the country in the decisions about the fate of the region. The integration of the country into the select group of signatory States that develop cutting-edge research in Antarctica is the main directive of this plan. By understanding the strategic-geopolitical importance of Antarctica to Brazil, and the role of science in the ATS politics, this thesis proposes new challenges and paradigms to the Brazilian Antarctic science, supporting to the current Strategic Planning for PROANTAR (2012 - 2022) and the most recent Action Plan for the Antarctic Science (2013 - 2018). Thus, the analysis of PROANTAR from the perspective of the definition of a strategic-scientific project and its geopolitical repercussions are the main objetives of this thesis, which are reflected in the following goals: an analysis of the Antarctic geopolitics, which determined a preliminary discussion regarding the geopolitical premises of the Treaty and the Antarctic science from a historical perspective; an analysis of the geopolitical dimensions of the region at the benning of the 21st century, identifying the year 1991 (ratification of the Madrid Protocol) as the ATS turning point, when the scientific-environmental dimension began to acquired a greater geopolitical relevance; an analysis of the Antarctic question in the Brazilian geopolitical line of thought, which allowed the discussion about the construction of a possible Antarctic territorial imaginary, as well as its repercussion on the scientific dimension of PROANTAR. Finally, we analyze the new challenges to the Brazilian Antarctic science in the 21st century: the geographic expansion of the PROANTAR research in that continent, especially the investigations into the Antarctic ice sheet, breaking the paradigm of a peripheral science that has been historically confined to the Antarctic Peninsula region; and the institution of a policy that guarantees the quality of the scientific production through an adequate logistic-financial support. Overcoming such challenges is paramount for the inclusion of the Brazilian Antarctic research in the so-called emerging frontiers of science. Nonetheless, as we analyze the political-scientific actions, converging to the definition of a Brazilian strategic project for Antarctic, which has been implemented since the beginning of the century, it becomes clearer the contradictions and obstacles to the definition of such project become: the bureaucratic hindrances and the volatile political actions, which in addition to the lack of recognition of the (geo)political relevance of a cutting-edge Antarctic science, especially by a large part of the scientific community working at PROANTAR, prevent the institution of a the scientific politicy and the definition of a strategic-scientific project for the region.

O presente trabalho visa analisar a produção científica brasileira no contexto das pesquisas realizadas no ambiente antártico, a qual envolve cientistas e não cientistas, civis e militares. O objetivo geral desta pesquisa é analisar os fatores que constroem a ciência brasileira no contexto do Programa Antártico Brasileiro - PROANTAR, mapeando atores e instituições que formam o Programa, considerando o contexto de produção dessa ciência, bem como os aspectos sociais que permeiam a construção do conhecimento científico no PROANTAR. Analisa-se a produção científica no PROANTAR, a partir do conceito de arenas transepistêmicas de Karin Knorr-Cetina, o qual compreende a ciência como um produto das negociações de cientistas e não cientistas, cada um com seus interesses e argumentos, este atores juntos trabalham com o objetivo de realizar um projeto comum, no caso o desenvolvimento do Programa Antártico Brasileiro. É possível afirmar que há uma arena transepistêmica em torno ao Programa Antártico Brasileira, a qual mobiliza os atores que possuem interesses relativos ao PROANTAR, interesses que são relativos e próprios dos segmentos científico, logístico, ambiental e político e na busca pela realização destes estabelecem negociações na arena. Por outro lado, há o trabalho conjunto das distintas epistemes da arena para que seja possível manter as atividades brasileiras na Antártica. / This study aims to analyze the Brazilian scientific production in the context of research conducted in the Antarctic environment, which involves scientists and nonscientists, civil and military. The general aim of this research is to analyze the factors that build the Brazilian science in the context of the Brazilian Antarctic Program, mapping out actors and institutions that make up the Program, considering the context of production of this science and the social aspects that underlie the construction of scientific knowledge in PROANTAR. Scientific production in PROANTAR is analyzed by the concept of transepistemic arenas of Karin Knorr Cetina, which understand science as a product of negotiations by scientists and nonscientists, each one with their concerns and arguments, this actors work together in order to accomplish a joint project, the development of the Brazilian Antarctic Program in this context. We will approach the scientists as members of a scientific community that is heterogeneous. In addition to a literature review on the topic, this paper presents the analysis of interviews with scientists and non-scientists linked to PROANTAR as well as the analysis of documents produced by the bodies responsible for the Program. It is expected that this work can contribute to the planning of the new directions of PROANTAR, through an analysis of negotiations and interests among the actors in the transepistemic arenas of PROANTAR.

Le bilan d'énergie de surface du Plateau Antarctique est essentiellement contrôlé par les propriétés physiques des premiers centimètres du manteau neigeux. Or l'évolution de cette neige de surface est complexe car elle dépend de processus fondamentalement imbriqués: vitesse de métamorphisme, profils de température, pénétration du rayonnement solaire, précipitations, transport de neige par le vent, etc. L'objectif de ces travaux de thèse est d'étudier ces diverses composantes et leur couplage afin de simuler l'évolution de la densité de la neige et de la taille de grain (surface spécifique) sur le Plateau Antarctique. Pour représenter de manière physique l'absorption de l'énergie solaire à l'intérieur du manteau, un modèle de transfert radiatif à fine résolution spectrale (TARTES) a été implémenté dans le modèle de manteau neigeux détaillé Crocus. TARTES permet de calculer le profil vertical d'absorption d'énergie dans un manteau stratifié dont les caractéristiques sont connues. Parmi elles, la forme des grains, explicitement prise en compte dans TARTES, a été peu étudiée jusqu'à présent. C'est pourquoi une méthode de détermination expérimentale de la forme optique des grains est proposée et appliquée à un grand nombre d'échantillons de neige. Cette méthode, basée sur des mesures optiques, des simulations TARTES, et l'inférence bayésienne, a permis de déterminer la forme la plus adéquate pour simuler les propriétés optiques de la neige, et a mis en évidence le fait que représenter la neige par un ensemble de particules sphériques conduisait à surestimer la profondeur de pénétration du rayonnement d'environ 30%. L'impact de l'absorption en profondeur du rayonnement sur les profils de température dans le manteau et son métamorphisme est ensuite étudié par des approches analytique et numérique, mettant en valeur la sensibilité des profils aux propriétés de la neige proche de la surface. En particulier, la densité de la neige sur les premiers centimètres est cruciale pour le bilan d'énergie du manteau car elle impacte à la fois la profondeur de pénétration du rayonnement et la conductivité thermique du manteau. Puisque le modèle Crocus tient compte de ce couplage entre propriétés optiques et physiques du manteau, il est utilisé pour estimer l'influence des conditions météorologiques sur la variabilité temporelle des propriétés physiques de la neige de surface à Dôme C. Ces simulations sont évaluées au regard d'un jeu de données collectées lors de missions de terrain et de mesures automatiques de l'albédo spectral et de la pénétration du rayonnement dans la neige. Ces observations mettent en évidence le rôle primordial des précipitations dans les variations rapides de taille de grain en surface et l'existence d'un cycle saisonnier de cette taille de grain. Ces variations sont bien simulées par Crocus lorsque le forçage atmosphérique qui lui est imposé est adéquat. En particulier, l'impact du vent sur l'évolution du manteau est fondamental car il contrôle la densité de surface par le biais du transport de neige. Ce transport est aussi à l'origine de la variabilité spatiale des propriétés de la neige observée à Dôme C. C'est pourquoi une modélisation stochastique de l'érosion et du transport de neige dans Crocus est proposée. En plus d'expliquer la variabilité spatiale de la densité et de la taille de grain, elle permet de reproduire celle de l'accumulation annuelle ainsi que les variations rapides de hauteur de neige liées à des épisodes de vent. Ces travaux ont permis une meilleure représentation des processus physiques qui contrôlent les variations des propriétés de la neige de surface à Dôme C, tout en soulignant le rôle primordial du vent, dont l'impact sur le manteau est particulièrement complexe à simuler. / The surface energy balance of the Antarctic Plateau is mainly governed by the physical properties of the snowpack in the topmost centimeters, whose evolution is driven by intricated processes such as: snow metamorphism, temperature profiles variations, solar radiation penetration, precipitation, snow drift, etc. This thesis focuses on the interactions between all these components and aims at simulating the evolution of snow density and snow grain size (specific surface area) on the Antarctic Plateau. To physically model the absorption of solar radiation within the snowpack, a radiative transfer model with high spectral resolution (TARTES) is implemented in the detailed snowpack model Crocus. TARTES calculates the vertical profile of absorbed radiation in a layered snowpack whose characteristics are given. These characteristics include snow grain shape, a parameter that has been seldom studied. For this reason, an experimental method to estimate the optical grain shape is proposed and applied to a large number of snow samples. This method, which combines optical measurements, TARTES simulations and Bayesian inference, is used to estimate the optimal shape to be used in snow optical models. In addition, it highlights that representing snow as a collection of spherical particles results in overestimation of the penetration depth of solar radiation. The influence of the penetration of solar radiation on the snow temperature profiles is then investigated with analytical and numerical tools. The results point out the high sensitivity of the temperature profiles to surface snow physical properties. In particular, the density of the topmost centimeters of the snowpack is critical for the energy budget of the snowpack because it impacts both the effective thermal conductivity and the penetration depth of light. To simulate the evolution of snow physical properties at Dome C by taking into account their interdependence with snow optical properties, the model Crocus is used, driven by meteorological data. These simulations are evaluated against a set of data collected during field missions as well as automatic measurements of snow spectral albedo and penetration depth. These observations highlight the influence of weather conditions on the temporal variability of surface snow properties. They show the existence of a slow decrease of snow grain size at the surface during summer. Rapid changes are also observed, essentially due to precipitation. These variations are well simulated by Crocus when forced by an appropriate atmospheric forcing. In particular, the impact of wind on the evolution of the snowpack is crucial because it controls the surface density through snow transport. This transport is also responsible for the spatial variability of snow properties observed at Dome C. That is why a stochastic representation of snow erosion and transport in Crocus is proposed. It explains well the observations of the spatial variability of density and grain size, and reproduces the variability of the annual accumulation as well as rapid changes in snow height resulting from drift events. This study improves our understanding of the physical processes which drive the properties of snow close to the surface on the Antarctic Plateau, and also points out the critical role of wind, the impact of which is very difficult to account for in models yet.

Apesar da pequena influência antrópica direta em seu território, a Antártida não pode ser considerada livre do alcance de poluentes. No presente estudo, avaliou-se a distribuição e transferência de poluentes orgânicos (PCBs, pesticidas organoclorados e PBDEs) em compartimentos abióticos (neve e água de degelo) e bióticos (liquens, musgos, invertebrados, peixes, ovos de aves e tecidos de aves e pinípedes, para os quais também foi aplicada análise isotópica de nitrogênio-15 e carbono-13) do ecossistema da Baía do Almirantado. Os compartimentos abióticos tiveram concentrações entre 1,4 e 156 pg L-1, apenas para grupos de organoclorados, com variação intra-sazonal importante e compatibilidade com níveis tróficos inferiores e amostras de vegetação, que por sua vez refletiram a importância de fontes secundárias de poluentes. Nos animais, grosso modo, os compostos prevalecentes (em ng g-1 peso úmido) foram PCBs, (6,82-1821), HCB (0,060-136) e DDTs, (0,410-524), níveis de duas a três ordens de grandeza superiores aos encontrados em vegetação. PBDEs ocorreram, de modo geral, em níveis uma ou duas ordens de grandeza abaixo dos organoclorados. A análise isotópica mostrou-se útil como ferramenta indicadora de nível trófico e origem de matéria orgânica consumida, correlacionando-se quantitativa e qualitativamente com os poluentes orgânicos pela indicação de fatores como stress nutricional e mudança de área de forrageio e/ou de dieta. Como alternativa, foi proposto um novo indicador de biomagnificação baseado no peso molecular dos PCBs, que apresentou resultados estatisticamente superiores ao ?15N na maioria dos casos. / Despite the small antropic direct influence on its territory, Antarctica cannot be considered out of pollutants\' reach. The present study evaluated the distribution and transfer of organic pollutants (PCBs, organochlorine pesticides and PBDEs) in both abiotic (snow and melting water) and biotic (lichens, mosses, invertebrates, fishes, bird eggs and bird and pinnipeds\' tissues, for which was also applied carbon-13 and nitrogen-15 stable isotopes analyses) compartments of the ecosystem from Admiralty Bay. Abiotic compartments showed concentrations between 1,4 and 156 pg L-1, only for organochlorine groups, with considerable intraseasonal variation and compatibility with lower trophic levels and vegetation samples, which in turn reflected the importance of secondary pollutants sources. In animal samples, grosso modo, the prevailing compounds were (in ng g-1 wet weight) PCBs (6,82-1821), HCB (0,060-136) and DDTs, (0,410-524), levels from two to three orders of magnitude superior to the ones found in vegetations. PBDEs occurred, in a general way, in levels from one to two orders of magnitude lower than the organochlorines. Stable isotope analyses proved useful as an indicator tool for trophic level and consumed organic matter, correlating itself in a qualitative and quantitative way with the organic pollutants by indication of factors as nutritional strees and variation in foraging areas and/or diet. As an alternative, a new biomagnifications indicator based on PCBs molecular weight was proposed, showing results statistically superior to the ?15N in the majority of the cases.