Dams are designed and assessed based on traditional factor of safety methodology. Several drawbacks of this approach exist; for example varying failure probability for structures where the factor of safety is the same. This traditional factor of safety methodology imposes conservative assumptions in terms of both design and analysis. A probability-based analysis has been suggested to account for the omission of uncertainties and provide a less conservative analysis (Westberg & Johansson, 2014). Through the stability analyses of three existing dam structures, a minimum level of reliability or maximum failure probability may be calculated with the ultimate goal of defining a target safety index (β-target) for buttress and gravity dams. These analyses shall in turn contribute to the formulation of a probability-based guideline for the design and assessment of Swedish concrete dams. This probability-based guideline shall be known as the ‘Probabilistic Model Code for Concrete Dams.’ The calculations carried out in this study adhere to the methodologies and specifications set out in the preliminary draft of the Probabilistic Model Code for Concrete Dams. These methodologies encompass analyses within two dominating failure modes for concrete dams; sliding stability and overturning stability. Various load combinations have been modelled for each dam structure to account for the probabilistic failure of each dam under commonly occurring circumstances. A parametric study has been carried out in order to provide insight into the contribution that existing rock bolts provide to the stability of each dam. Furthermore, a study has been carried out into the existence of a persistent rock joint or failure plane in the rock foundation and the effects its presence would have on the sliding stability of a dam. Finally a discussion had been carried out in order to provide suggestions into the formulation of a target safety index through the data envisaged by our analyses for the design and assessment of Swedish concrete dams.

The purpose of this thesis is to evaluate the contribution of grouted rock bolts on the stability of concrete dams. The load capacity of the grouted rock bolts are assessed considering eventual deteriorating processes. An additional objective was to compare the resulting load capacity with the prevailing regulations in RIDAS (the power companies’ guidelines on dam safety) and possibly suggest new guideline values. The literature study consists of two parts; concrete dams and grouted rock bolts. In the first part concrete dams are discussed and especially the inherent forces and aspects when controlling their stability. The second part treats grouted rock bolts and the theoretical focus is on their function and possible failure modes as well as on the degrading processes (primarily corrosion) that are affecting the rock bolts.  Subsequently, the theory was applied on the Swedish concrete buttress dam Storfinnforsen, which is the largest concrete dam in Sweden. The dam was selected for this study mainly because its shape is archetypical for buttress dams. In addition, a digitalized model of the dam was obtainable from previous research projects.  A numerical analysis with the finite element analysis software ABAQUS was performed in order to evaluate the stability of the dam and to support the analytical analysis. The load capacity of the grouted rock bolts was analytically evaluated with consideration to eventual degradation. Assuming a corrosion rate of 60 μm/year, the grouted rock bolts in Storfinnforsen could after 100 years be trusted with a load capacity of approximately 180 MPa. That load capacity is due to shear failure, which constitutes the most plausible failure mode for rock bolts in buttress dams. The value 180 MPa is to be seen in contrast to the current limitation of 140 MPa that is defined in RIDAS (2011). The conclusion of this thesis is accordingly, that the maximum allowed load capacity that can be assigned the grouted rock bolts in the stability calculations of concrete dams can be increased from todays 140 MPa. This conclusion is substantiated by the analytical analyses with the numerical calculations as support.

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.

Em escalas interanuais a advecção de calor, sal e nutrientes pode afetar a produtividade primária. Pode-se citar a Circulação de Revolvimento Meridional (MOC) no impacto da concentração de clorofila. Neste estudo, a partir do método Multidimensional Empirical Mode Decomposition foram obtidos tendências decadais de PAR, nitrato integrado na coluna d\'água, concentração de clorofila e fluxo de volume da MOC. Em variações de baixa frequência há uma relação entre o transporte de volume da MOC com o nitrato integrado na coluna d\'água no Atlântico Sul, e consequentemente, na concentração de clorofila. Dois possíveis cenários foram identificados sobre o efeito da MOC no nitrato integrado e na concentração de clorofila. O cenário 1 apresenta uma relação direta no sistema MOC-nitrato integrado-concentração de clorofila, enquanto o efeito do cenário 2 é indireto, com a MOC afetando outras variáveis que perturbam o sistema. Neste estudo também foi analisado a influência de teleconexões atmosféricas na MOC do Atlântico Sul. Foi achado indícios da influência da Oscilação Antártica na MOC do Atlântico Sul em escalas decadais. Conclui-se que variações de baixa frequência no fluxo de volume da MOC alteram o padrão espaço-temporal da concentração de clorofila no Atlântico Sul. / On interannual timescales the advection of heat, salt and nutrients can affect the primary production. The influence of the Meridional Overturning Circulation (MOC) over the chlorophyll concentration can be mentioned. In this study, decadal trends of PAR, integrated nitrate over the water column, chlorophyll and volume flux of the MOC were obtained using the Multidimensional Empirical Mode Decomposition method. On low frequency variations there is a relationship between the MOC volume transport with integrated nitrate over the water column in the South Atlantic, and therefore, on chlorophyll concentration. Two scenarios were identified as possible mechanisms of influence of the MOC over integrated nitrate and chlorophyll concentrations. Scenario 1 presents a direct relationship on the system MOC-integrated nitrate-chlorophyll concentration, while scenario 2 has an indirect effect, with the MOC affecting other variables that disturb the system. In this study the influence of atmospheric teleconnections on the South Atlantic MOC were also investigated. It was found evidence that the Antarctic Oscillation can affect the South Atlantic MOC on decadal timescales. It was concluded that low frequency variability on the volume flux of the MOC can alter the spatiotemporal pattern of the chlorophyll concentration on the South Atlantic.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-09-27T14:22:18Z No. of bitstreams: 1 Dissertac...pdf: 4004750 bytes, checksum: c28f16763d698bcdf286109327f4a3a0 (MD5) / Made available in DSpace on 2017-09-27T14:22:18Z (GMT). No. of bitstreams: 1 Dissertac...pdf: 4004750 bytes, checksum: c28f16763d698bcdf286109327f4a3a0 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A porção equatorial Oeste do Atlântico Sul é uma região-chave para o estudo das variabilidades climáticas, já que esta área é a principal saída de calor e sal para as altas latitudes do hemisfério norte através da Corrente Norte do Brasil. Esta transferência inter-hemisférica é um dos fatores cruciais para o funcionamento da circulação termohalina no oceano Atlântico, conhecida como Atlantic Meridional Overturning Circulation (AMOC). Baseado nisto, o objetivo deste trabalho é apresentar uma reconstrução da temperatura da superfície do mar (TSM) ao longo dos últimos 40.000 anos, em um intervalo que engloba o Ultimo Máximo Glacial (UMG) e o Holoceno. Para isto, foram empregados três testemunho sedimentares recuperados na margem Nordeste do Brasil. Dois destes testemunhos (MC 17/2 e MC 11/1) tiveram sua cronologia combinada, para juntos formarem um registro único do Holoceno. O terceiro testemunho (MC 10/3) enfoca o UMG e a fase de degelo até o início do Holoceno. Como proxies para a reconstrução paleoceanográfica da TSM foram empregados o isótopo estável de oxigênio (δ18Oc) do foraminífero planctônico Globigerinoides ruber (branco 250 – 300 μm), a Técnica do Análogo Moderno (TAM) e a análise faunística da assembleia de foraminíferos planctônicos na fração 150 μm. Os resultados para o UMG mostram a existência de dois cenários distintos que se separam em 21 k anos AP. Antes desta data condições mais frias na ordem de 2 ºC existiram na região, como ficou evidenciado pelos valores mais positivos do δ18Oc, pelas menores TSM reconstruídas pela TAM e pela maior abundância de foraminíferos planctônicos relacionados a produtividade e profundidade, como Globigerina glutinata, Neogloboquadrina dutertrei, Globorotalia truncatulinoides (dextral e sinistral) e Globorotalia inflata. Após 21 k anos AP uma forte transição ocorre no δ18Oc e na abundância absoluta de foraminíferos planctônicos, indicando a entrada de condições mais quentes na região, principalmente durante o evento Heinrich 1 (H1) e o Younger Dryas (YD). Este intervalo, que inclui a fase de degelo e parte do Holoceno é marcado pela redução das espécies relacionada a produtividade e profundidade e pelo aumento das espécies de águas quentes e superficiais. O retorno da espécie Globorotalia menardii em 21 k anos AP pode indicar a reativação do transporte de águas quentes do Oceano Índico para o Atlântico Sul realizado pela Corrente das Agulhas durante a fase de degelo. Os dados apresentados aqui demonstram que o Atlântico equatorial Oeste responde a entrada de água doce no Atlântico Norte e ao transporte de águas quentes via Corrente das Agulhas, e que o balanço destes dois fatores foi crucial para o retorno da AMOC no fim do UMG. Os resultados para o Holoceno mostraram que a região vem sofrendo um aumento progressivo da TSM da ordem de 1 ºC principalmente após o Holoceno médio, onde alterações nos padrões orbitais podem ter modificado a distribuição da energia solar no planeta. Análises espectrais sobre os dados mostram uma série de periodicidade quase cíclicas centradas em 4.1 – 3.8 kyr, 1.5 – 1.0 kyr, ~ 700 yr, 570 – 560 yr, ~ 390 yr, ~350 yr e ~ 330 yr e podem refletir a ação de forçantes climáticas externa (variabilidade solar) e internas (sistema oceano-atmosfera) transmitidas pela circulação termohalina globalmente. / The western equatorial Atlantic is a key region for the study of climate variability, as this area is the main source of heat and salt toward high latitudes of northern Atlantic through the North Brazil Current. This interhemispheric transfer is one of the crucial factors for the thermohaline circulation in the Atlantic Ocean, known as Atlantic Meridional Overturning Circulation (AMOC). Based on this, the aim of this work is to show a reconstruction of sea surface temperature (SST) over the last 40,000 years, into a range that comprises the Last Glacial Maximum (LGM) and Holocene. For this, we used three sedimentary records recovered in Northeast Brazilian margin. Two of these records (MC 17/2 e MC 11/1) were combined to generate a single record of Holocene. The last record comprises the LGM until the early Holocene. As proxies for the reconstruction of SST were employed the oxygen stable isotope (δ18Oc) of planktonic foraminifera Globigerinoides ruber (white 250 – 300 μm), the Modern Analogue Technique (MAT) and the assemblage of planktonic foraminifera in the size-fraction of 150 μm. The results for the LGM showed the existence of two different scenarios that were separated at 21 kyr BP. The heavier oxygen values recorded prior to 21 kyr BP demonstrated that the Last Glacial Maximum was up to 2ºC colder than Holocene. After 21 kyr BP, a strong shift to lighter values indicated the onset of warmer conditions during deglacial, especially during Heinrich event 1 and the Younger Dryas. The planktonic foraminifera assemblage as species related to productive or deep waters confirmed the conditions indicated by the oxygen composition; i.e., Globigerinita glutinata, Neogloboquadrina dutertrei, Globorotalia truncatulinoides (left and right coiling) and Globorotalia inflata were more abundant prior to 21 kyr BP. With the increase in the sea surface temperature after 21 kyr BP, the abundance of these species was reduced, particularly for G. glutinata and G. inflata, and the abundance of species found in warmer waters increased, especially for Globigerinella siphonifera. The species Globorotalia menardii, which was absent in the Last Glacial Maximum, reappeared after 21 kyr BP, which may have been a response to the Agulhas Leakage that released warmer waters into the South Atlantic at the beginning of deglacial. The data presented here indicate that the western equatorial Atlantic responded to the meltwater pulse at high latitudes of the northern Atlantic and to warm waters from the Indian Ocean. The balance between these two factors was crucial to the development of the Atlantic Meridional Overturning Circulation at the end of the LGM. The results of Holocene showed that the region has suffered a gradual increase in SST of around 1 ºC, mainly after the mid-Holocene, where changes orbital patterns may have changed the distribution of solar energy on the planet. Spectral analyzes on the data demonstrated a series of periodicities centered at 4.1 – 3.8 kyr, 1.5 – 1.0 kyr, ~ 700 yr, 570 – 560 yr, ~ 390 yr, ~350 yr e ~ 330 yr and can be related of climate forcing transmitted globally by the thermohaline circulation.

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.

O objetivo do presente estudo foi investigar a resposta da assembleia de foraminíferos planctônicos frente às variações paleoceanográficas superficiais na porção oeste do Atlântico Sul, o qual desempenha um papel fundamental na Célula de Revolvimento Meridional do Atlântico (AMOC, Meridional Overturning Circulation). Para esta finalidade, foi analisado um registro sedimentar marinho contínuo desde o Último Máximo Glacial até o presente, com base na assembleia de foraminíferos planctônicos, isótopos de oxigênio e na razão Mg/Ca. Adicionalmente, foram avaliadas as variações na ocorrência e na geoquímica dos dois morfotipos de G. ruber (branca), principal espécie utilizada em estudos paleoceanográficos de regiões tropicais e subtropicais. Os resultados mostraram que as diferenças geoquímicas e de abundância relativa dos morfotipos de G. ruber branca evidenciam dois grupos de espécimes ecologicamente distintos, confirmando que o morfotipo sensu stricto calcifica em menores profundidades com relação ao morfotipo sensu lato e que reconstituições paleoceanográficas baseadas no uso não-seletivo dos morfotipos poderiam ser tendenciosas. A Análise Fatorial realizada nos dados de abundância relativa dos foraminíferos planctônicos identificou 4 fatores principais: o Fator 1, representado pelas espécies G. tenella, G. calida, e G. rubescens e relacionado com a temperatura subsuperficial; o Fator 2, representado pelas espécies N. incompta, N. dutertrei e G. truncatulinoides, relacionado com a profundidade da termoclina; o Fator 3, representado pela espécie G. bulloides, associado com o processo de ressurgência e o Fator 4, representado pelas espécies G. ruber e G. glutinata, associado com a intensidade da Corrente do Brasil. As variações mais expressivas de paleotemperatura e paleosalinidade da superfície do mar e da fauna de foraminíferos planctônicos estão relacionadas com os eventos climáticos abruptos do Hemisfério Norte ocorridos durante a deglaciação, tendo sido moduladas pelas variações de arranjo e intensidade da AMOC. Durante os eventos frios Heinrich 1 e Younger Dryas, relacionados a um enfraquecimento da AMOC, foi observado um aumento das paleotemperatura e paleosalinidade e da intensidade da Corrente do Brasil (Fator 4). Contrariamente, durante o evento quente Bolling-Allerod, a paleotemperatura e a paleosalinidade diminuíram expressivamente, como resposta à retomada da AMOC, e houve aumento da produtividade e presença de uma termoclina mais rasa (Fatores 2 e 3). Sugere-se ainda, que entre 26 e 15 ka houve um deslocamento para norte da Confluência Brasil-Malvinas, possivelmente alcançando a latitude da área de estudo (∼23°S), inferido pela presença da espécie G. inflata. Durante o Holoceno, também foi registrada variação significativa na intensidade da Corrente do Brasil, indicada pelos valores máximos do Fator 4 em torno de 7 ka. O reaparecimento das espécies do plexo G. menardii se deu em 8 ka, assim como o aumento das espécies de foraminíferos planctônicos subsuperficiais, indicado pelo Fator 1. Essas mudanças no Holoceno foram atribuídas à entrada efetiva das águas quentes e salinas do Oceano Índico via vazamento das Agulhas, as quais foram essenciais para o restabelecimento da AMOC moderna. / The objective of the present study was to investigate the response of the planktonic foraminiferaassemblage to the superficial paleoceanographic variations in the western South Atlantic, which plays a key role in the AMOC. For this purpose, a continuous marine sedimentary record was analyzed from the Late Glacial Maximum to the present, based on the planktonic foraminifera assemblage, oxygen isotopes and the Mg/Ca ratio. In addition, variations in the occurrence and geochemistry of the two morphotypes of G. ruber (white) were evaluated. This is the main species used in paleoceanographic studies of tropical and subtropical regions. The results showed that the geochemical and relative abundance differences between the G. ruber morphotypes show two ecologically distinct groups of specimens, confirming that the morphotype sensu stricto calcifies at lower depths with respect to the morphotype and sensu lato, and paleoceanographic and paleoceanographic reconstructions using non-selective mixture of morphotypescould potentially be biased. The Factorial Analysis identified four factors: Factor 1, represented by G. tenella, G. calida, and G. rubescens, is related to the subsurface temperature; Factor 2, represented by N. incompta, N. dutertrei and G. truncatulinoides is related to the depth of the thermocline; Factor 3, represented by G. bulloides, is related toupwelling; and Factor 4, represented by G. ruber and G. glutinata, is related to the intensity of the Brazil Current. The results showed that the most significant variations of paleotemperature and paleosalinity and the planktonic foraminifera assemblage are related to the abrupt climatic events of the Northern Hemisphere occurred during deglaciation and were modulated by variations in AMOC arrangement and intensity. During the cold events Heinrich 1 and Younger Dryas, related to a weakening of the AMOC, an increase of paleotemperature and paleosalinity and intensity of the Brazil Current (Factor 4) in the western portion of the South Atlantic was observed. Conversely, during the hot event Bolli-Allerod, paleotemperature and paleosalinity decreased expressively, as a response to AMOC resumption, with increased productivity and presence of a shallower thermocline (Factors 2 and 3). It is also suggested that between 26 and 15 ka there was a displacement to the north of the Brazil-Malvinas Confluence, possibly reaching the latitude of the study area (∼23°S), inferred by the presence of the G. inflata. Along the Holocene, there was also a significant variation in the intensity of the Brazil Current, indicated by the maximum values of Factor 4 around 7ka. The reappearance of G. menardii plexus occurred in 8ka, as well as the increase of the species of subsurface planktonic foraminifera, indicated by Factor 1. These changes in the Holocene were attributed to the effective entrance of the hot and saline waters from the Indian Ocean via the Agulhas Leakage, which were essential for the reestablishment of the modern AMOC.

O objetivo do presente estudo foi investigar a resposta da assembleia de foraminíferos planctônicos frente às variações paleoceanográficas superficiais na porção oeste do Atlântico Sul, o qual desempenha um papel fundamental na Célula de Revolvimento Meridional do Atlântico (AMOC, Meridional Overturning Circulation). Para esta finalidade, foi analisado um registro sedimentar marinho contínuo desde o Último Máximo Glacial até o presente, com base na assembleia de foraminíferos planctônicos, isótopos de oxigênio e na razão Mg/Ca. Adicionalmente, foram avaliadas as variações na ocorrência e na geoquímica dos dois morfotipos de G. ruber (branca), principal espécie utilizada em estudos paleoceanográficos de regiões tropicais e subtropicais. Os resultados mostraram que as diferenças geoquímicas e de abundância relativa dos morfotipos de G. ruber branca evidenciam dois grupos de espécimes ecologicamente distintos, confirmando que o morfotipo sensu stricto calcifica em menores profundidades com relação ao morfotipo sensu lato e que reconstituições paleoceanográficas baseadas no uso não-seletivo dos morfotipos poderiam ser tendenciosas. A Análise Fatorial realizada nos dados de abundância relativa dos foraminíferos planctônicos identificou 4 fatores principais: o Fator 1, representado pelas espécies G. tenella, G. calida, e G. rubescens e relacionado com a temperatura subsuperficial; o Fator 2, representado pelas espécies N. incompta, N. dutertrei e G. truncatulinoides, relacionado com a profundidade da termoclina; o Fator 3, representado pela espécie G. bulloides, associado com o processo de ressurgência e o Fator 4, representado pelas espécies G. ruber e G. glutinata, associado com a intensidade da Corrente do Brasil. As variações mais expressivas de paleotemperatura e paleosalinidade da superfície do mar e da fauna de foraminíferos planctônicos estão relacionadas com os eventos climáticos abruptos do Hemisfério Norte ocorridos durante a deglaciação, tendo sido moduladas pelas variações de arranjo e intensidade da AMOC. Durante os eventos frios Heinrich 1 e Younger Dryas, relacionados a um enfraquecimento da AMOC, foi observado um aumento das paleotemperatura e paleosalinidade e da intensidade da Corrente do Brasil (Fator 4). Contrariamente, durante o evento quente Bolling-Allerod, a paleotemperatura e a paleosalinidade diminuíram expressivamente, como resposta à retomada da AMOC, e houve aumento da produtividade e presença de uma termoclina mais rasa (Fatores 2 e 3). Sugere-se ainda, que entre 26 e 15 ka houve um deslocamento para norte da Confluência Brasil-Malvinas, possivelmente alcançando a latitude da área de estudo (∼23°S), inferido pela presença da espécie G. inflata. Durante o Holoceno, também foi registrada variação significativa na intensidade da Corrente do Brasil, indicada pelos valores máximos do Fator 4 em torno de 7 ka. O reaparecimento das espécies do plexo G. menardii se deu em 8 ka, assim como o aumento das espécies de foraminíferos planctônicos subsuperficiais, indicado pelo Fator 1. Essas mudanças no Holoceno foram atribuídas à entrada efetiva das águas quentes e salinas do Oceano Índico via vazamento das Agulhas, as quais foram essenciais para o restabelecimento da AMOC moderna. / The objective of the present study was to investigate the response of the planktonic foraminiferaassemblage to the superficial paleoceanographic variations in the western South Atlantic, which plays a key role in the AMOC. For this purpose, a continuous marine sedimentary record was analyzed from the Late Glacial Maximum to the present, based on the planktonic foraminifera assemblage, oxygen isotopes and the Mg/Ca ratio. In addition, variations in the occurrence and geochemistry of the two morphotypes of G. ruber (white) were evaluated. This is the main species used in paleoceanographic studies of tropical and subtropical regions. The results showed that the geochemical and relative abundance differences between the G. ruber morphotypes show two ecologically distinct groups of specimens, confirming that the morphotype sensu stricto calcifies at lower depths with respect to the morphotype and sensu lato, and paleoceanographic and paleoceanographic reconstructions using non-selective mixture of morphotypescould potentially be biased. The Factorial Analysis identified four factors: Factor 1, represented by G. tenella, G. calida, and G. rubescens, is related to the subsurface temperature; Factor 2, represented by N. incompta, N. dutertrei and G. truncatulinoides is related to the depth of the thermocline; Factor 3, represented by G. bulloides, is related toupwelling; and Factor 4, represented by G. ruber and G. glutinata, is related to the intensity of the Brazil Current. The results showed that the most significant variations of paleotemperature and paleosalinity and the planktonic foraminifera assemblage are related to the abrupt climatic events of the Northern Hemisphere occurred during deglaciation and were modulated by variations in AMOC arrangement and intensity. During the cold events Heinrich 1 and Younger Dryas, related to a weakening of the AMOC, an increase of paleotemperature and paleosalinity and intensity of the Brazil Current (Factor 4) in the western portion of the South Atlantic was observed. Conversely, during the hot event Bolli-Allerod, paleotemperature and paleosalinity decreased expressively, as a response to AMOC resumption, with increased productivity and presence of a shallower thermocline (Factors 2 and 3). It is also suggested that between 26 and 15 ka there was a displacement to the north of the Brazil-Malvinas Confluence, possibly reaching the latitude of the study area (∼23°S), inferred by the presence of the G. inflata. Along the Holocene, there was also a significant variation in the intensity of the Brazil Current, indicated by the maximum values of Factor 4 around 7ka. The reappearance of G. menardii plexus occurred in 8ka, as well as the increase of the species of subsurface planktonic foraminifera, indicated by Factor 1. These changes in the Holocene were attributed to the effective entrance of the hot and saline waters from the Indian Ocean via the Agulhas Leakage, which were essential for the reestablishment of the modern AMOC.

In this paper I’m studying Toni Morrison’s short story Recitatif (2022) through the perspective of deconstruction. I theorise about conceptual meanings and differences that occur and can be found in structures. With deconstruction I can observe where in the text traces of metaphysics lay and what impact they have on the characters that live within the story. The study examines binary oppositions such as white and black; male and female; being rich and being poor; being somebody and being nobody. Questions are raised about found meaning in these categories, what they entail and say about perception of reality, and how all of these categories fit into one much bigger classification: the human. This study follows the text closely, exploring the story in chronological order and focuses on the two main characters, Twyla and Roberta, who symbolise two different ends of the binary opposition white and black skinned. Twyla and Roberta come to define themselves by their contrasts and that is also where deconstruction flows and exists. In the end, it’s the character Maggie – first seen as ”unimportant” – that comes to play a crucial part in the shaping of the story and Twyla and Roberta’s lives. Therefore, through deconstruction and its terms and notions, I further investigate Maggie’s character and her meaning and place in Recitatif. This study concludes with that while binary oppositions – and the perceptions they comprise – are firmly established around the characters and the world so are they not fully bound by them. / I den här uppsatsen genomför jag en läsning av Toni Morrisons novell Recitatif (2022) utifrån det teoretiska perspektivet dekonstruktion. Genom dekonstruktion synliggör, analyserar och problematiserar jag konceptuella världsuppfattningar och strukturer. Jag observerar var i texten metafysik finns och vilken påverkan det har på karaktärerna i berättelsen. I uppsatsen undersöks dikotomier och binära motsättningar såsom vit och svart; man och kvinna; rik och fattig; att vara betydelsefull och att vara oväsentlig. Till följd av dessa strukturella indelningar och inramningar väcks frågor om verklighetsuppfattning och mening samt att de därutöver ingår i en gemensam kategori: människan. Denna uppsats gör en textnära läsning och följer berättelsen i kronologisk ordning med fokus på de två huvudkaraktärerna, Twyla och Roberta, som symboliserar två olika sidor i den binära motsättningar vit och svart hudfärg. Twyla och Robertas mening och föreställning om omvälden samt identitet uppstår genom att deras likheter och olikheter ställs i kontrast mot varandra vilken dekonstruktion blottlägger. Till slut visar det sig dock att karaktären Maggie – som man först inte tror spelar en stor roll i novellen – har en betydande inverkan på berättelsen och hon kommer att omdefiniera både Tywlas och Robertas verklighetsuppfattning. Därför, genom dekonstruktionsperspektivet, undersöker jag Maggies karaktär och vilken funktion den fyller i Recitatif. Uppsatsen avslutas med slutsatsen att medan binära motsättningar – och de konceptuella världsuppfattningar som uppstår till följd av dem – starkt påverkar karaktärerna och världen är de dock inte helt och hållet bundna att förhålla sig efter dem.

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