The strength of the Atlantic meridional overturning circulation (AMOC) is believed to be associated with changes in surface buoyancy in the subpolar North Atlantic, which naturally leads to a notion that the AMOC has been weakening under global warming. Yet, a variety source of observations and its assimilation into ocean circulation models have not supported such an AMOC decline so far. In this study, an aspect that has not been paid attention, regarding the maintenance of the AMOC strength, is explored: storm activity in the subpolar North Atlantic (NA). An analysis using reanalysis data shows that the wintertime turbulent heat flux variability in the LS deep convection region is largely controlled by a small number of extreme heat flux event days, suggesting a pivotal role of winter storms in prompting LS deep-water formation. A set of forced ocean-ice model simulations, in which synoptic winter storm activity associated with these event days is either suppressed or doubled over the subpolar NA, confirms the above analysis as the altered storm activity results in a substantial change in LS convection and the AMOC strength. These experiments also show an upward AMOC trend during the late twentieth century, the degree of which is to some extent related to the intensity of storm activity in the LS. The upward AMOC trend found in the first part of the dissertation opposes to a downward AMOC trend in the twentieth century coupled model simulations employing the identical ocean component. An analysis suggests that contrast to the ocean-ice model, storm activity in the LS convection region and associated heat flux decreases during the late twentieth century. Although there is also a buoyancy increase over the LS, the wintertime heat flux decrease appears to be a more dominant factor for a decrease in convection in the LS, as an increasing freshwater input from Arctic/Subarctic Ocean bypasses the interior LS along the western boundary current. Therefore, the downward AMOC trend in the coupled model can be linked ultimately to the decreasing storm activity over the LS. This study therefore suggests that storm activity over the major convection regions needs to be paid further attention in assessing AMOC variations, including long-term trend in response to a warming scenario, in future studies.

Data de aprova??o retirada da vers?o impressa do trabalho. / ?rea de concentra??o: Produ??o Vegetal. / Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-08-14T22:18:43Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) camila_rodrigues_costa.pdf: 5661319 bytes, checksum: b9deab885dfc53d90534a8a979f8d00d (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-10-05T19:35:26Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) camila_rodrigues_costa.pdf: 5661319 bytes, checksum: b9deab885dfc53d90534a8a979f8d00d (MD5) / Made available in DSpace on 2018-10-05T19:35:26Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) camila_rodrigues_costa.pdf: 5661319 bytes, checksum: b9deab885dfc53d90534a8a979f8d00d (MD5) Previous issue date: 2018 / Funda??o de Amparo ? Pesquisa do estado de Minas Gerais (FAPEMIG) / As turfeiras s?o ambientes de transi??o entre os ecossistemas terrestres e aqu?ticos, formados pela acumula??o sequencial de mat?ria org?nica. Extremamente sens?veis as mudan?as nos padr?es de precipita??o e temperatura, as turfeiras s?o consideradas verdadeiros arquivos da evolu??o do ambiente ao seu redor. Nas depress?es das ?reas dissecadas da Serra do Espinha?o Meridional, Minas Gerais, ocorrem ambientes propicios para forma??o de turfeiras. Dentre elas encontra-se a turfeira do Rio Preto (18?14'5,25"S e 43?19'7,24" WGS, 1.593 m.s.m) inserida no Parque Estadual do Rio Preto. A turfeira do Rio Preto ? colonizada por diferentes fisionomias do Bioma Cerrado principalmente o Campo ?mido e Campo Rupestre, sendo encontrados ainda redutos de Floresta Estacional Semidecidual (Cap?es de Mata). O objetivo deste trabalho foi reconstituir as mudan?as paleoambientais ocorridas desde o final do Pleistoceno Tardio. Para isto foi utilizada uma abordagem multi-proxy, consistindo em estratigrafia do perfil do solo da turfeira, an?lises palinol?gicas, de is?topos est?veis (13C e 15N), de composi??o geoqu?mica e data??es radiocarb?nicas. A idade mais antiga, obtida da base do testemunho, foi de 23.037 anos cal. AP, indicando que a forma??o da turfeira se deu a partir do Pleistoceno Tardio. A partir da an?lise conjunta dos proxys foi poss?vel inferir cinco principais fases de mudan?as paleoambientais: RP-I, entre ~ 23.037 e 13.500 anos cal. AP, clima bastante ?mido e frio, possibilitando a presen?a de indicadores de Floresta Montana e o empobrecimento do sinal isot?pico. Este foi um per?odo de bastante instabilidade na bacia hidrogr?fica da turfeira, inferida pelo alto teor de Si, indicador de sinal de material mineral local; RP-II, entre ~13.500 e 11.700 anos cal. AP, ligeiro aumento da temperatura e queda na umidade levando a redu??o de indicadores de clima frio e a expans?o da vegeta??o campestre. No entanto as condi??es ainda eram mais ?midas e frias que as atuais, e a ind?cios de diminui??o do sinal de material mineral local; RP-III, entre ~11.700 e 8.500 anos cal. AP, tend?ncia de aumento da temperatura e diminui??o da umidade em conjunto com a mudan?a da vegeta??o de plantas C3 para C4, causando a forte retra??o das Floresta Estacional Semidecidual e Floresta Montana, em conjunto aumento do fluxo de sinal de material mineral local; RP-IV, entre ~8.500 e 7.000 anos cal. AP, condi??es de clima ainda mais seco e quente, causando o desaparecimento dos indicadores de clima frio, retra??o do Campo ?mido e expans?o do Campo Rupestre. Per?odo de bastante estabilidade da bacia hidrogr?fica da turfeira, sugerido pelo baixo conte?do de material mineral; RP-V, de 7.000 anos cal. AP at? o presente, clima era novamente mais ?mido e temperaturas mais amenas, semelhante ?s condi??es atuais, aumento na acumula??o de turfa, possibilitando o reaparecimento dos indicadores de Floresta Montana e Floresta Estacional Semidecidual junto com a retra??o do Campo, e diminui??o da entrada de material mineral. Flutua??es no clima influenciaram fortemente as mudan?as na paleovegeta??o e na estrutura sedimentar do registro da turfeira do Rio Preto. Devido ? import?ncia das turfeiras, n?o s? como arquivo de mudan?as paleoambientais, mas tamb?m pelos seus servi?os ambientais (armazenamento de ?gua e de carbono), estes ambientes precisam ser melhores protegidos. / Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Produ??o Vegetal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2018. / The peatlands are transitional environments between terrestrial and aquatic ecosystems, formed by the sequential accumulation of organic matter. Extremely sensitive to changes in precipitation and temperature patterns, peatlands are real archives of the evolution of the environment around them. In Serra do Espinha?o Meridional, Minas Gerais State, Brazil, in depressions of the dissected areas occurs an environment conducive to formation of peatlands. Among them the peatland of Rio Preto (18?14'5,25"S e 43?19'7,24" WGS, 1.593 m.s.m), located in the Rio Preto State Park. The area is colonized by different vegetation physiognomy of the Cerrado Biome, mainly Rupestre Fields and Wet Fields, beyond of redoubts of Semidecidual Stationary Forests, called Capon Forests. The area is colonized by different vegetation physiognomy of the Cerrado Biome, mainly Rupestre Fields and Wet Fields, beyond of redoubts of Semidecidual Stationary Forests, called Capon Forests. The objective of this work was to reconstruct the paleoenvironmental changes that have occurred since the Late Pleistocene. The work was constituted by the application of a multi-proxy approach, such as peatland soil stratigraphy, palynological analyzes, stable isotopes (13C and 15N), geochemical composition analyzes and 14C dating. The oldest age obtained at the base of the peatland profile was 23.037 cal. years BP, indicating that the formation of the peatland occurred during the Late Pleistocene. In this study it was possible to infer five main stages of paleoenvironmental changes: RP-I ~23.000-13.500 cal. years BP, very cold climate and very humid, presence of Montana Forest indicators and impoverishment of the isotopic signal, period of instability in hydrographic basin of the peatland; RP-II ~13.500-11.700 cal. years BP, small increase in temperature and decreased humidity, reduction of the indicators of cold climate and the expansion of the field vegetation, however the climatic conditions were more humid and cooler than the current, decrease of the entrance of local mineral material; RP-III ~11.700-8.500 cal. years BP, trend of increased temperature and decreased humidity, change in vegetation from C3 to C4 plants, reduction of the Semideciduous Seasonal Forest and Mountain Forests, increased flow of local mineral material; RP-IV ~8.500-7.000 cal. years BP, drier and hotter weather, causing the disappearance of the indicators of cold weather, retraction of the Wet Field and expansion of Rupestre Field. Period of very stability in the watershed of the peatland; RP-V 7.000 cal. years BP until present, increased humidity and decrease in temperature, as current conditions, increased accumulation of peat, reappearance of the indicators of Montana Forest and Seasonal Semideciduous Forest and retraction of the Field, decrease of regional and local dust. Fluctuations in the climate influenced changes in paleovegetation and the sedimentary structure of the peatland Rio Preto. Given the value of peatlands as archives of paleoenvironmental changes and their environmental functions, these environments need to be better protected.

Made available in DSpace on 2016-06-02T19:29:26Z (GMT). No. of bitstreams: 1 3113.pdf: 7591482 bytes, checksum: 45160b07f4c8f5a70b6480fc6a52d7f3 (MD5) Previous issue date: 2009-11-05 / This study aimed to describe the hydro-ecological aspects of Mariana Hydrographic Basin, tributary of the river Taxidermista, Alta Floresta, MT, Brazil. Therefore, studies were performed on the morphometry of the basin; land use; floristic, vegetation structure and correlation with the distribution of tree species and soils of the riparian forest; dynamics of runoff; water physical-chemical aspects; and socio-economy aspects. These results indicate the strong structural drainage control of basin, however the current land use, dominated by cattle farm and deforestation, contribute to erosion. Furthermore, the riparian vegetation is in secondary successional stage probably due to preterit human disturbance. Soil and tree species correlation showed soil texture as attribute greater importance in the distribution of plant groups. The dynamics of runoff showed a low capacity of water storage basin. The water physical-chemical aspects results were directly related to the land use, and the parameters Color, Turbidity and Total Phosphorus presented themselves as the most suitable for monitoring water quality and environmental degradation. The basin is occupied by colonos from the process of private colonization occurred in the mid 1970 s and is predominated by small farms, many over-used, the average monthly income is directly related to its size. The failure of agriculture established at the time of colonization conditioned the uncontrolled deforestation for pasture and, since then, extensive cattle farming is predominant. Thus, the current land use, and the settlement historical processes of the region caused important environmental changes that are directly related to basin s sustainability, especially those related to water shortage. Therefore, it is necessary to implement recuperation and restructuring degraded areas program and the strengthening of family agriculture, aiming to economic and environmental sustainability. / O presente trabalho teve como objetivo descrever hidro-ecologicamente a Bacia Hidrográfica Mariana, afluente do rio Taxidermista, Alta Floresta, MT. Para tanto, foram realizados estudos sobre a morfometria da bacia hidrográfica; uso e cobertura da terra; florística, estrutura e correlação com a distribuição das espécies arbóreas e os solos da mata ciliar; dinâmica do escoamento superficial; aspectos físico-químicos da água; e aspectos sócioeconômicos. Os resultados demonstraram haver um forte controle estrutural da drenagem da bacia hidrográfica, entretanto o atual uso e cobertura do solo, predominado pela pecuária e o desmatamento, contribuem para processos erosivos. A vegetação ciliar encontra-se em estágio sucessional secundário muito provavelmente em função de perturbações antrópicas pretéritas. A correlação entre o solo e as espécies arbóreas evidenciou a textura do solo como atributo de maior importância na distribuição dos grupos vegetais. A dinâmica do escoamento superficial demonstrou a baixa capacidade de armazenamento hídrico da bacia. Os aspectos físico-químicos da água apresentaram resultados diretamente relacionados com o uso e cobertura da terra, sendo que os parâmetros Cor, Turbidez e Fósforo Total apresentaram-se como os mais indicados para o monitoramento da qualidade da água e da degradação ambiental. A bacia é ocupada por colonos provenientes do processo de colonização privada ocorrida em meados na década de 1970 com predomínio de pequenas propriedades, muitas delas sobre-utilizadas, onde a renda média mensal é diretamente relacionada com o tamanho das mesmas. O insucesso da agricultura implantada no momento da colonização condicionou o desmatamento desordenado para a produção de pastagens e, desde então, a pecuária extensiva é predominante. Assim, o atual uso e cobertura da terra, e os processos históricos de ocupação da região causaram alterações ambientais importantes e que estão diretamente relacionados com a sustentabilidade da bacia, principalmente aquela relacionada com a escassez hídrica. Portanto, é necessário a implantação de um programa de recuperação e reestruturação de áreas degradadas e do fortalecimento da agricultura familiar, com vistas a sustentabilidade econômica e ambiental.

The social transformations in the South Levantine Neolithic show two basic tendencies: 1) complex social structures are replaced by less complex ones, before more complex social structures develop; and 2) most likely connected to that: heterarchical and hierarchical patterns are linked together in varying ways; the more needs for social regulation appear, the more heterarchical elements trigger corporate, hierarchical and central structures, and new sedentary types of conflict occur. The development of family and communal life modes moved as shifting waves through the ecozones of the southern Levant: core household structures (MPPNB) are replaced by corporate extended families households (LPPNB) which then again are replaced by core household structures (FPPNB-PNA-B); heterarchical communities (PPNA) get replaced by hierarchical (MPPNB-LPPNB) communities, before pastoral-heterarchical communities develop (FPPNB-PNA-B) and exist together with the hierarchical permanent settlements of the FPPNB-PNA-B. The qualities and momentum of this general development may differ according to regional ecological conditions, including reversible and conservative regional developments. / Las transformaciones sociales del Neolítico en el Levante meridional denotan dos tendencias básicas: 1) las estructuras sociales complejas son reemplazadas por otras de características menos elaboradas en una etapa previa al despliegue de estructuras sociales más complejas, y 2) probablemente en forma paralela, se entrelazan principios heterárquicos y jerárquicos del orden social en proporciones cambiantes. Con la creciente demanda de una regulación de los elementos heterárquicos, estos desaparecen para ser sustituidos por estructuras jerárquicas corporativas y centrales, por lo que aparecen nuevas formas sedentarias de conflicto. El desarrollo de las formas de vida familiares y comunales atravesó, a manera de olas consecutivas, los diferentes paisajes del Levante meridional: estructuras familiares nucleares (en el PPNB Medio) fueron reemplazadas por estructuras familiares extensas corporativas (PPNB Tardío) y volvieron, luego, a su estado inicial (PPNB Final a PNA-B). Las comunidades heterárquicas (PPNA) se convirtieron en jerárquicas (PPNB Medio a PPNB Tardío) antes del surgimiento de comunidades heterárquicas pastoriles (PPNB Final a PNA-B) que coexistieron, en forma paralela, con asentamientos jerárquicos permanentes (PPNB Final a PNA-B). Las cualidades y la velocidad de este proceso general dependen, en forma especial, de factores ecológicos regionales e incluyen desarrollos regionales de carácter tanto reversible como conservador.

Nesta tese vou apresentar novos dados sobre padrões de ocupação dos Jê Meridionais e minhas interpretações sobre a história deste povo, com base em meu estudo de caso, do Alto Rio Canoas, região de Urubici, em Santa Catarina, Brasil. No planalto, os camposde altitude e a mata de araucária dominam a paisagem. Nas serrarias de Urubici, as nascentes de vários arroios e rios começam em zonas húmidas, com solos rasos e pedregosos, na área dos campos, a cerca de 1800m de altitude. Estas águas correm através de vales incisos florestados pela mata de araucária criando cachoeiras e corredeiras, que acabam por se transformar no meândrico Rio Canoas, que flui no meio de um vale largo e plano, em torno de 1000m acima do nível do mar. A montanhosa região de Urubici foi intensamente pesquisada na década de 60, mas depois disso, a pesquisa ficou estagnada. Os principais pontos deste projeto foram: Primeiro, foram revisadas e atualizadas as pesquisas anteriores, revisitando a maioria dos sítios arqueológicos mapeados na década de 60, atribuindo-lhes coordenadas geográficas, fotos e mapas, e descrições ambientais recentes. Segundo, além da visita aos sítios mapeados previamente, foi realizado um mapeamento oportunista de novos sítios, baseado em entrevistas com membros da comunidade local, o que gerou um novo mapa arqueológico da região. Terceiro, com base nessas informações e nas novas escavações em sítios específicos, iniciou-se a reflexão sobre as paisagens Jê do Sul, com o objetivo de compreender a história de longo prazo e o sistema de assentamento da tradição arqueológica Taquara-Itararé. Quarto, a partir das análises de grãos de amido de fitólitos, a partir de restos carbonizados de alimento aderidos a parede da cerâmica coletada na escavação do sítio Bonin, foram obtidos novos dados, importantíssimos para pensar novas formas de interpretação na arqueologia da tradição Taquara-Itararé. Tais análises trouxeram evidências de produção de alimentos como Zea mays, Cucurbitasp., Manihotsp., e o consumo alimentar de Phaseolussp. e Dioscoreasp. entre outros, o que, sem dúvida, é uma chave para pensar em outro tipo de organização social, mobilidade e economia para os povos proto-Jê Meridional. Em quinto lugar, no sentido de pensar uma \"estratigrafia paisagem do Jê Meridional\" um banco de dados SIG foi utilizado como uma ferramenta para criar modelos virtuais de, por exemplo, a análise visibilidade acumulada entre sítios e análise de rotas de menor custo. / In this thesis I will present new data on Southern Jêsettlement patterns, and my interpretations regarding the history of these people, based on my case study, from the Upper Canoas River, Urubici region, in Santa Catarina state, Brazil. On the highland plateau, the High Altitude Grasslands (or Campos) and the Paraná Pine Forest dominate the landscape. In the Urubici hills, various headwaters begin in wetland areas, with shallow and rocky soils, on Campos, around 1800m altitude. These waters flow through incised valleys forested by Paraná Pine and create waterfalls and rapids, which eventually turn into the meandering Canoas River that flows in the middle of a wide and flat valley, around 1000m above sea level. The mountainous Urubici region was intensively researched in the 60\'s, but after that, research wasstagnated. The main points of this project were: First, I reviewed and updated previous research, which involved relocating the sites mapped in the 60\'s, assigning them geographical coordinates, photos and maps, and improving environmental descriptions. Second, I carried out an inspection of previously recorded sites and carried out opportunistic survey, based on interviews with members of the local community, looking for new sites, and making a new archaeological map of the region. Third, based on this information and my new excavations at targeted sites, I aimed to think about the Southern Jê landscapes, with a view to understanding the long-term history and the settlement pattern of the Taquara-Itararé archaeological tradition. Fourth, starch grain and phytoliths analysis from charred food remains founded in pottery, collected at Bonin site excavation, achieved important new data for new interpretive ways on Taquara-Itararé archaeology, bringing to us food production evidences of Zea mays, Cucurbitasp., Manihotsp., and food consumption of Phaseolussp.,Dioscoreasp. and others, what is a key to think another kind of social organization, mobility and economy for southern proto-Jê people. Fifth, in a way to think the \"southern Jê landscape stratigraphy\" aGIS database were used like a tool to create virtual models of, for example, cumulative viewshed analysis and least coast pathway analysis.

Les cils motiles et statiques jouent d’importants rôles dans la détermination de l’axe gauche-droite (GD) qui, en général, est mis en place par l’intermédiaire de flux directionnels générés dans des structures spécialisées appelées organisateurs gauche-droite (OGD). C’est ce point clé du développement qui dictera une organogenèse asymétrique. Dans mon projet de thèse, nous avons développé une méthode, appelée 3D-Cilia Map, et analysé l’organisation tridimensionnelle de l’implantation des cils afin d’extraire les paramètres clés responsables de la mise en place du flux directionnel et par conséquent de l’asymétrie GD. En résumé, nos résultats suggèrent qu’un mécanisme de signalisation chimique serait le plus plausible pour induire la rupture de la symétrie GD. Plus tard, les cellules réguleront intrinsèquement l’orientation asymétrique des cils à leur surface. Le travail présenté ici contribue de façon importante à nos connaissances actuelles concernant le comportement des cils et les mécanismes de sensation des flux dans l’établissement de l’axe gauche droite au sein de l’organisateur gauche-droite du poisson zèbre. / Both motile and immotile cilia play important roles in left-right (LR) axis determination, which generally involves cilia-mediated directional flows in organized structures (LR organizers, LRO) in which the LR symmetry is broken, thus driving asymmetric organogenesis in the developing embryos. In my PhD project we aimed to developed a method (3D-Cilia Map) and analyze the three-dimensional organization of ciliary implantation in order to extract the key parameters modulating the directional flow involved in breaking the axis of symmetry in the zebra fish LRO. Altogether, our results suggest the initial mechanism to break the LR symmetry is most likely to be based on the transport of achemical signal, while later, cells intrinsically provide their cilia the cues to orient asymmetrically. The work presented here represents an important contribution to our current understanding of cilia behaviors and flow-sensing mechanisms in the establishment of the left-right axis in the zebra fish LRO.

Equatorial plasma bubbles (EPBs) are large structures consisting of depleted plasma that generally form on the nightside of Earth's ionosphere along magnetic field lines in the upper thermosphere/ionosphere. While referred to as `bubbles', EPBs tend to be longer along magnetic latitudes and narrower along magnetic longitudes which are on the order of thousands and hundreds of kilometers, respectively. EPBs are a well documented occurrence with observations spanning many decades. As such, much is known about their general behavior, seasonal variation of occurrences, increasing/decreasing occurrences with increasing/decreasing solar activity, and their ability to interact and interfere with radio waves such as GPS. This dissertation expands on this understanding by focusing on the detection and tracking of EPBs in the upper thermosphere/ionosphere along equatorial to low latitudes. To do this, far ultraviolet (FUV) emission observations of the recombination of O$^+$ with electrons via the Global-Scale Observations of the Limb and Disk (GOLD) mission are analyzed. GOLD provides consistent data from geostationary orbit with the eastern region of the Americas, Atlantic, and western Africa. The optical data can be used to pick out gradients in brightness along the 135.6 nm wavelength which correlate with the location of EPBs in the nightside ionosphere. The dissertation provides a novel method to look at and analyze 2-dimensional data with inconsistent time-steps for EPB detection and tracking. During development, preprocessing of large scale (multiple years) data proved to be the largest time sync. To that end, this dissertation tests the possibility of using convolution neural networks for detection of EPBs with the end goal of reducing the amount of preprocessing necessary. Further, data from the Ionospheric Connection Explorer's (ICON's) ion velocity meter (IVM) are compared to EPBs detected via GOLD to understand how the ambient plasma around the EPBs behave. Along with the ambient plasma, zonal and meridional thermospheric winds observed by ICON's Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument are analyzed in conjunction with the same EPBs to understand how winds coincident with EPBs behave. An analysis of winds before EPBs form is also done to observe the potential for both zonal and meridional winds' ability to suppress and amplify EPB formation. / Doctor of Philosophy / Equatorial plasma bubbles (EPBs) are large structures that generally form during post- sunset along Earth's magnetic equator. While referred to as `bubbles', EPBs tend to be thousands of kilometers from north to south and hundreds of kilometers from east to west and well over a thousands kilometers in altitude. EPBs are a well documented occurrence with observations spanning many decades. This includes their ability to interfere with radar and GPS. This dissertation expands on the scientific community's understanding by focusing on the detection and tracking of EPBs along the magnetic equator. To do this, observations from the NASA Global-Scale Observations of the Limb and Disk (GOLD) mission are analyzed. GOLD provides consistent observations looking over the eastern region of the Americas, Atlantic, and western Africa. A unique method to look at and analyze this data for EPB detection and tracking is developed. This dissertation also tests the possibility of using machine learning for detection of EPBs. Further, data from the NASA Ionospheric Connection Explorer (ICON) mission is compared to EPBs detected via GOLD to understand how the behavior of the upper atmosphere and the conductive region therein, known as the ionosphere, interact with the EBPs themselves.

La circulation méridienne de retournement (MOC) de l’Atlantique Nord est une composante clé du système climatique global, via son rôle dans la redistribution de chaleur, d’eau douce et de propriétés chimiques entre hautes et basses latitudes. Aux moyennes et hautes latitudes, le Courant Nord-Atlantique(NAC) forme la branche haute de la MOC. Il s’écoule vers le nord-est à la frontière des gyres subpolaire et subtropical, et se divise en deux branches principales dans l’est du gyre subpolaire : une branche nord qui recircule vers l’ouest dans le gyre subpolaire et une branche sud qui alimente les mers Nordiques.Une simulation réaliste haute résolution (ORCA025-G70, 1/4°) est combinée à un outil d’analyse Lagrangienne pour étudier la variabilité de la MOC (1965-2004) à travers la section A25-Ovide qui joint le Portugal au Groenland. Deux cellules de retournement vertical sont identifiées : une cellule subtropicale connectant les hautes et basses latitudes et une cellule interne aux régions subpolaires. La variabilité décennale de la MOC est associée à des changements synchronisés des apports subtropical et subpolaire dans la NAC. Ce dernier subit d’importantes restructurations horizontales caractérisées par la variabilité opposée de ses deux branches. Ces modifications de la distribution horizontale du transport sont principalement régies par la variabilité de l’afflux subtropical.Les variations du transport de chaleur à travers A25-Ovide sont la cause principale de la variabilité du contenu de chaleur observée dans l’est du gyre subpolaire (1965-2004). La variabilité du transport de chaleur résulte d’un déséquilibre entre des changements opposés de ses composantes « vitesse » et « température ». Les anomalies de vitesse et température sont en partie reflétées dans des déplacements verticaux d’isopycnes, potentiellement associés à la proportion changeante de masses d’eau subtropicales et subpolaires transportées par la branche nord du NAC.Enfin, une circulation surface-fond moyenne calculée depuis des mesures hydrographiques répétées et des mesures altimétriques indique une contribution mineure de la mer du Labrador pour la MOC global. Cependant, l’intensité du retournement diapycnal à AR7W a presque diminué de moitié entres les 1990’s et les 2000’s, confirmant l’importance de la région pour la variabilité basse-fréquence de la MOC. / The meridional Overturning Circulation (MOC) of the North Atlantic ocean is a key component of the global climate system, through its role in redistributing heat, freshwater end chemical properties between low and high latitude regions. In mid-high latitude regions, the North Atlantic Current (NAC) forms the upper limb of the MOC. It flows northeastward at the subtropical/subpolar boundary, and splits into two main branches in the eastern subpolar gyre: a northern branch that recirculates within the subpolar region and a southern branch that feed the Nordic Seas.A realistic eddy-permitting simulation (ORCA025-G70, 1/4°) is combined with a Lagrangian analysis tool (ARIANE) to investigate the MOC variability (1965-2004) across the A25-Ovide line, which joins Greenland to Portugal. Two vertical overturning cells are identified: a subtropical cell connecting low and high latitudes (12Sv) and a cell internal to the subpolar gyre (4Sv). The decadal MOC variability is associated with synchronized transport changes of the subtropical and subpolar inflow within the NAC. The latter undergoes important horizontal restructuring with opposed transport changes of its northern and southern branches. Those horizontal transport changes are largely induced by the horizontal variability of the subtropical inflow.Changes in oceanic heat transport across A25-Ovide are largely responsible for the observed heat content changes in the eastern subpolar gyre (1965-2004). Heat transport variability at A25-Ovide results from an imbalance between opposed changes in its velocity and temperature components. Both temperature and velocity anomalies are partly reflected in large scale heaves of isopycnals, and potentially relate to the varying proportion of warm subtropical waters and cold subpolar waters advected within the northern NAC branch.A 2000’s mean full-depth circulation computed along the merged AR7W/A25-Ovide line from repeated hydrographic profile and altimetry data indicates a minor contribution of the Labrador Sea to the basin wide mean MOC. However, the strength of the diapycnal overturning at AR7W has almost halved between the 1990’s and the 2000’s, confirming the importance of the region for the low-frequency MOC Variability.

Le but de cette thèse est d’analyser les impacts de la variabilité atmosphérique grande échelle sur la circulation océanique. Ceci a déjà fait l’objet de nombreuses publications, dans lesquelles la variabilité atmosphérique est analysée en termes de modes de variabilité, déterminés par analyse en composantes principales (EOF en anglais) des anomalies de pression de surface. Ces modes sont l’Oscillation Nord-Atlantic (NAO), le Pattern Est-Atlantique (EAP) et le Pattern Scandinave (SCAN). La décomposition en EOF implique que les modes sont orthogonaux et symétriques. Cette dernière hypothèse a été montrée comme étant invalide pour la NAO. Par conséquent, un nouveau concept est proposé dans cette étude pour estimer la variabilité atmosphérique, celui des régimes de temps. Ces derniers sont des structures spatiales de grande échelle, récurrents et quasi-Stationnaires qui permettent de capturer la variabilité des forçages atmosphériques. De plus, ils permettent de séparer les patterns spatiaux des deux phases de la NAO. Ces régimes de temps sont donc une alternative prometteuse pour l’analyse de la variabilité océanique forcée par l’atmosphère. A partir d’observation et de modèles numériques (réalistes ou idéalisés), nous avons montré que les régimes Atlantic Ridge (AR), NAO− et NAO+ induisent une réponse rapide (échelles mensuelles à interannuelles) des gyres subtropical et subpolaire (via un mécanisme de Sverdrup topographique) et de la cellule de retournement (MOC, ajustement aux anomalies de transport d’Ekman). Aux échelles décennales, le gyre subpolaire s’intensifie lors de conditions NAO+ et BLK persistantes via un ajustement barocline aux flux de flottabilité et s’affaiblit pour AR via un ajustement barocline aux anomalies de rotationnel de vent. Ce dernier mécanisme explique aussi l’augmentation du gyre subtropical pour une NAO+ persistante et son affaiblissement pour un AR persistant. La réponse des gyres pour des conditions de NAO− persistantes est un déplacement vers le sud des gyres (l’intergyre gyre). L’intensité de la MOC est augmentée pour des conditions de NAO+ et BLK persistantes, dû à l’augmentation de la formation d’eau dense en mer du Labrador, et inversement pour NAO− et AR. Finalement, des bilans de contenu de chaleur dans la gyre subpolaire et les mers nordiques ont été effectués dans quatre modèles océaniques globaux. Les moyennes d’hiver de convergence océanique de chaleur dans la partie ouest de la gyre subpolaire sont positivement corrélées aux occurrences d’hiver de NAO−, ce qui est dû à la présence de l’intergyre, tandis que cette convergence est négativement corrélée aux occurrences d’AR, ce qui est dû à la réduction des deux gyres qui lui est associée. Les flux de chaleur vers l’océan dans la gyre subpolaire sont négativement corrélés aux occurrences d’hiver de la NAO+ et inversement pour la NAO−. Dans les mers Nordiques, ils sont positivement corrélés aux occurrences de BLK et, dans une moindre mesure, aux occurrences de AR. De plus, nous suggérons que la variabilité du contenu de chaleur dans la partie ouest du gyre subpolaire est la réponse décalée (lag de 6 ans) à l’intégration temporelle du forçage lié au régime NAO+, due à la combinaison de la réponse en phase (0-Lag) des flux de chaleur et à la réponse décalée (lag de 3 ans) de la convergence de chaleur. / The aim of the PhD is to investigate the impacts of the large-Scale atmospheric variability on the North- Atlantic ocean circulation. This question has already been addressed in a large number of studies, in which the atmospheric variability is decomposed into modes of variability, determined by decomposing sea-Level pressure anomalies into Empirical Orthogonal Function (EOFs). These modes of variability are the North-Atlantic Oscillation (NAO), the East-Atlantic Pattern (EAP) and the Scandinavian Pattern (SCAN). EOF decomposition assumes that the modes are orthogonal and symmetric. The latter assumption, however, has been shown to be inadequate for the NAO. Hence, a different framework is used in this study to assess the atmospheric variability, the so-Called weather regimes. These are large-Scale, recurrent and quasi-Stationary atmospheric patterns that have been shown to capture well the interannual and decadal variability of atmospheric forcing to the ocean. Furthermore, they allow to separate the spatial patterns of the positive and negative NAO phases. Hence, these weather regimes are a promising alternative to modes of variability in the study of the ocean response to atmospheric variability. Using observations and numerical models (realistic or in idealised settings), we have shown that the Atlantic Ridge (AR), NAO− and NAO+ regimes drive a fast (monthly to interannual) wind-Driven response of the subtropical and subpolar gyres (topographic Sverdrup balance) and of the meridional overturning circulation (MOC, driven by Ekman transport anomalies). At decadal timescales, the subpolar gyre strengthens for persistent NAO+ and Scandinavian Blocking (BLK) conditions via baroclinic adjustment to buoyancy fluxes and slackens for persistent AR conditions via baroclinic adjustment to wind-Stress curl anomalies. The latter mechanism also accounts for the strengthening of the subtropical gyre for persistent NAO+ conditions and its weakening for persistent AR conditions. The gyres response to persistent NAO− conditions reflects the southward shift of the gyre system (the intergyre gyre). The MOC spins-Up for persistent NAO+ and BLK conditions via increased deep water formation in the Labrador Sea, and conversely for the NAO− and AR regimes. Last, heat budget calculations in the subpolar gyre and the Nordic Seas have been performed using four global ocean hindcasts. The winter averaged heat convergence in the western subpolar gyre is positively correlated with the NAO− winter occurrences, which is due to the intergyregyre circulation, while it is negatively correlated with AR winter occurrences, because of the wind-Driven reduction of both gyres. Downward surface heat flux anomalies are negatively correlated with NAO+ occurrences, and conversely for the NAO−. In the Nordic Seas, they are positively correlated with BLK and to a lesser extent AR occurrences. Furthermore, we suggest that the heat content variability in the western subpolar gyre is the signature of the delayed response (6-Year lag) to the time-Integrated NAO+ forcing, due to the combination of the immediate (0-Lag) response of surface heat flux and the lagged (3 year lag) response of ocean heat convergence.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The distribution of arboreal and shrub species is related to different environmental conditions. The general goal of this study was to evaluate the influence of environmental factors in structure of communities and dynamics of the natural regeneration in Deciduous Seasonal Forest stretch, located in Quarta Colônia State Park, Agudo, RS, Brazil. The specific goals were to differentiate the structure and floristic of clusters (floristic groups) of the arboreal component, determining which environmental variables influenced the forest structure, identifying what changes have occurred in a year of natural regeneration monitoring and identifing which variables limited or facilitated the establishment of arboreal and shrub populations. Three levels of inclusion were used for sampling forest communities: arboreal component (diameter at breast height (DBH) ≥ 5 cm), sampled in 33 plots of 20 m x 20 m (1.32 ha); natural regeneration Class I (1 cm ≤ DBH < 5 cm), sampled in sub-plots of 4 m x 10 m (0.132 ha); and natural regeneration Class II (DBH < 1 cm and height ≥ 20 cm), sampled in sub-plots of 4 m x 2.5 m (0.033 ha). Cluster II showed the highest average diameter (40.0 cm) and the basal area (1.353 m2 plot-1= 33.825 m2 ha-1). The highest richness (70 species) occurred in Cluster I. The two clusters showed negative exponential diameter distribution, common to the forests with self-regeneration capacity. The species with more developed structure in natural regeneration was Trichilia elegans, Cupania vernalis and Actinostemon concolor, and Trichilia clausseni, Nectandra megapotamica and Allophylus edulis in arboreal component. The species of arboreal component showed association with relief, chemical and textural properties of soil and canopy characteristics, of which only the texture was not related to the regenerating species. The species with the highest value of Natural Regeneration Relative (RNR) kept their posts at the end of the measurements. Different values of Ingrowth Rate (IR), Mortality (MR) and Regeneration (RR); and height growth were detected. For example, the species Myrsine umbellata (TI = 58.3%; TM = 100%) and Annona rugulosa (TM = 37.5%; TM = -37.5%) have excelled in relation to the number of individuals fluctuations, while Baccharis sp. (73.3 cm) and Cabralea canjerana (2.5 cm) showed antagonistic values of height growth. Such changes have been influenced by ecological aspects, light dependence and dispersal strategy, and variables such as thickness (height) of accumulated litter and exposure of relief. The analysis of environmental correlations of the most abundant species indicated, for example, that Actinostemon concolor and Sorocea bonplandii were tolerant to shallow soils, with higher levels of stoniness, recurrent situation in forests of edge of the Southern Plateau, while Cupania vernalis and Nectandra megapotamica were correlated negative with these variables. The different relationships observed show that the use of shrub and tree species in ecological restoration should be based on the analysis of potentially favorable or limiting environmental variables. / A distribuição de espécies arbustivas e arbóreas está relacionada às diferentes condições ambientais. Nesse contexto, o objetivo geral deste estudo foi verificar a influência de fatores ambientais na estrutura de comunidades e na dinâmica da regeneração natural de espécies arbustivas e arbóreas, em um trecho de Floresta Estacional Decidual, localizado no Parque Estadual Quarta Colônia, Agudo - RS. Os objetivos específicos foram: diferenciar a estrutura e a florística de agrupamentos (grupos florísticos) do componente arbóreo; verificar quais variáveis ambientais influenciaram a estrutura da floresta; identificar quais alterações ocorreram em um ano de monitoramento da regeneração natural; identificar quais variáveis atuaram como limitantes ou facilitadoras do estabelecimento de populações arbóreas e arbustivas. As comunidades florestais foram amostradas em três níveis de inclusão: componente arbóreo (diâmetro à altura do peito (DAP) ≥ 5 cm), em 33 parcelas de 20 m x 20 m (1,32 ha); regeneração natural Classe I (1 cm ≤ DAP < 5 cm), em sub-parcelas de 4 m x 10 m (0,132 ha); e regeneração natural Classe II (DAP < 1 cm e altura ≥ 20 cm), em sub-parcelas de 4 m x 2,5 m (0,033 ha). Constatou-se que o Agrupamento II apresentou maiores valores de diâmetro (40,0 cm) e de área basal (33,825 m2/ha), enquanto o Agrupamento I teve maior riqueza (70 espécies). Os dois agrupamentos apresentaram distribuição diamétrica exponencial negativa, indicando que a floresta tem capacidade de autorregeneração. As espécies com estrutura mais desenvolvida na regeneração natural foram Trichilia elegans, Cupania vernalis e Actinostemon concolor e no componente arbóreo foram Trichilia clausseni, Nectandra megapotamica e Allophylus edulis. As espécies do componente arbóreo apresentaram distribuição relacionada ao relevo, propriedades químicas e textura do solo e características do dossel, das quais apenas a textura não teve relação com as espécies regenerantes. As espécies com maior valor de regeneração natural relativa (RNR) mantiveram seus postos ao final das medições. Detectaram-se diferentes valores para as taxas de ingresso (TI), mortalidade (TM) e regeneração (TR), além de incrementos em altura. Por exemplo, as espécies Myrsine umbellata (TI = 58,3%; TM = 100%) e Annona rugulosa (TM= 37,5%; TM = -37,5%) se destacaram em relação às flutuações do número de indivíduos, enquanto Baccharis sp. (73,3 cm) e Cabralea canjerana (2,5 cm) apresentaram valores antagônicos de crescimento em altura. Tais alterações foram influenciadas por aspectos autoecológicos, dependência de luz e estratégia de dispersão, e algumas variáveis como espessura (altura) da serapilheira acumulada e exposição do relevo. A análise de correlações ambientais das espécies mais abundantes indicou que Actinostemon concolor e Sorocea bonplandii foram tolerantes a solos rasos, com maior grau de pedregosidade, situação recorrente nas florestas do rebordo do Planalto Meridional, enquanto Cupania vernalis e Nectandra megapotamica apresentaram correlação negativa com essas variáveis. As diferentes correlações observadas evidenciam que o uso de espécies arbustivas e arbóreas na restauração florestal deve ser baseado na análise de variáveis ambientais, potencialmente favoráveis ou limitantes.