Using simulation data of a regional ocean model, Nardini et al. applied pathline predicates for a detailed post-hoc analysis of the Benguela upwelling system. In this work, we evaluate the accuracy of this technique. Using different temporal samplings, we aim at finding minimum requirements for the temporal resolution of the flow data in the context of retroactive particle pathline techniques. Besides the flow field, our simulation data contains synthetic tracer fields for different tracer source regions. Using the flow data, dense trajectories are computed to enable deriving ”emulated tracer fields” based on the local ratio of pathline particles originating from tracer source regions to other ones, which can then be compared to the original tracer fields. We find that the emulated tracer concentrations are overestimated in comparison to the original ones. However, the shape of the regions with high tracer concentration can be reproduced.

Beca JAE-Predoctoral CISC; Proyecto LARECO CTM2011-25929

Cette thèse s'intéresse à la dynamique océanique induite par les échelles spatiales et temporelles de l'atmosphère, et du vent en particulier, dans les régions d'upwelling du Benguela et des Canaries. Ces régions sont sous l'influence d'un vent local ou régional, soufflant parallèlement à la côte. "Moteur" principal de la résurgence d'eau froide, ce vent est modulé par des processus physiques à des échelles spatio-temporelles variées. La nature des interactions avec l'atmosphère, l'océan et le continent environnants diffère selon les processus. Depuis deux décennies, des efforts remarquables portent sur la description par télédétection des champs atmosphériques à la surface de l’océan. Un nombre croissant de missions spatiales et des améliorations techniques majeures ont permis de raffiner la résolution horizontale et temporelle des produits disponibles à l'échelle globale. La disponibilité de multiples mesures diffusiométriques grillées, traitées et distribuées par le LOSCERSAT,nous amène dans un premier temps à comparer et analyser la richesse et la finesse des échelles retranscrites par différents produits. Ainsi, plusieurs gammes d'échelles de vent sont différenciées et leurs signatures sur l'upwelling côtier sont étudiées. L'intensité des anticyclones subtropicaux (Sainte Hélène et Açores) module la saisonnalité de l'upwelling le long des côtes Ouest africaines. Les régions centrales des upwellings de l’Atlantique, sous l'influence permanente de ces centres de haute pression, sont ainsi les cellules d'upwelling les plus intenses de chacun des systèmes en termes de pérennité et d'intensité (cellule de Lüderitz et cellule de Dakhla respectivement dans l'hémisphère Sud et l'hémisphère Nord). À l'échelle régionale, ou l'échelle des sous-bassins (O(1000 km)), la variabilité intrasaisonnière du vent est contrôlée par le renforcement ou l'atténuation des anticyclones entraînant à la côte l'activation ou la relaxation d'événements d'upwelling. À des échelles plus petites (O(100 km)), le front caractéristique de température de surface (SST) entre la côte et le large façonne la structure spatiale du vent par des processus de stabilisation/déstabilisation de la colonne d'air. Un vent soufflant en direction de l'équateur et parallèlement à un front de SST aura tendance à diminuer (augmenter) sur le flanc froid (chaud) de ce front. Le rotationnel (la divergence) du vent est directement impacté(e) et répond linéairement, au premier ordre, à la composante du gradient de SST normale (tangentielle) à la direction du vent. Ces rétroactions océaniques sont caractérisées par une échelle temporelle allant de l'hebdomadaire au mensuel. Enfin, de fines échelles du vent sont couramment observées dans les premiers kilomètres de l’océan au voisinage de la côte. L’interface entre le large et le continent est en effet associée à un affaiblissement significatif des vents. L'extension zonale de cette transition (O(10 km)) dépend notamment de l'orographie et de la rugosité de surface du continent adjacent. L'impact d'une telle réduction du vent sur la structure des upwellings côtiers, la dynamique sous-jacente et le transport côte-large de particules est appréhendé à l'aide d'analyses numériques eulériennes et lagrangiennes. / This study focuses on the oceanic response to fine atmospheric spatial and temporal scales, and especially fine wind patterns in the Benguela and Canary upwelling systems. These regions are under the influence of local or regional wind, blowing parallel to the coast. Thewind is the main driver of the cold-water upwelling and is modulated by several physical processes at various scales. The nature of the interactions with the atmosphere, the ocean and the adjacent continent differs according to these processes. For the past 20 years, outstanding efforts have been made in the description and understanding of the atmospheric conditions at the sea surface. An increasing number of space missions and major technical improvements have allowed refinement of the horizontaland temporal resolution of the products available at global scale. The availability of multiple gridded scatterometer measurements,processed and distributed by the LOS-CERSAT, brings us first to compare and analyze the richness and fineness of the scales of a few products. We differentiate several wind scales and study their signatures on coastal upwelling dynamics. The intensity of the subtropical anticyclones (Saint Helena andAzores) modulates the seasonality of the upwelling along the Africanwest coast. The central regions of both upwelling systems are permanently under the influence of these atmospheric highs and,thus, are the most intense upwelling cells of each system, both interms of durability and intensity (Lüderitz and Dakhla cells for the southern and the northern hemisphere, respectively). On a regional scale, or basin scale (O(1000 km)), the intraseasonal wind variability is driven by the strengthening or weakening of these anticyclones, causing the activation or relaxation of upwelling events at the coast.At smaller scales (O(100 km)), the characteristic sea surface temperature (SST) front between the coastal and open ocean shapes the spatial structure of the wind by stabilization/destabilization of the air column. An equatorward-blowing wind parallel to an SST front tends to decrease (increase) on the cold side (warm) of this front. The curl (divergence) of the wind is directly impacted and the first order response varies linearly with the crosswind (downwind) SST gradient. This oceanic feedback is characterized by weekly to monthly temporal scales. Finally, small-scale wind structures are frequently observed in the first kilometers of the coastal ocean. Indeed, the interface between the open ocean and the continent is associated with a significant wind drop-off. The zonal extension of this transition (O(10 km) depends on the orography and on the surface roughness of the adjacent continent. The impact of such a wind reduction on the structure of the coastal upwelling, the underlying ocean dynamics and the cross-shore transport of particles is diagnosed with both Eulerian and Lagrangian numerical analyses.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2018-03-12T17:39:30Z No. of bitstreams: 1 Tese Manuel Moreira.pdf: 26683391 bytes, checksum: 22f4cca548ed444677c5428a580b351d (MD5) / Made available in DSpace on 2018-03-12T17:39:30Z (GMT). No. of bitstreams: 1 Tese Manuel Moreira.pdf: 26683391 bytes, checksum: 22f4cca548ed444677c5428a580b351d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / A acumulação dos elementos-traço nos sedimentos desempenha um importante papel na ciclagem destes elementos nos ambientes marinhos, associado a variáveis formas de retenção no reservatório sedimentar, em diferentes escalas temporais. No presente estudo foi avaliado o fracionamento geoquímico de Fe, Mn, As, Cd, Co, Cr, Cu, Mo, Ni, Pb e Zn entre as frações solúveis em HCl, associada à pirita (FeS2) e associada à fração orgânica, como forma de elucidar os processos que determinam a acumulação destes elementos nos sedimentos da plataforma continental do Sistema de Ressurgência de Cabo Frio (SRCF) nos últimos 8.000 anos. Foi observado que o fracionamento dos elementos Fe, Mn, As, Cr, Ni, Pb e Zn apresenta uma maior proporção na fração solúvel em HCl nos três testemunhos sedimentares coletados ao longo da plataforma continental. O Cu em todas as estações apresentou uma maior proporção na fração da matéria orgânica. O Cd (plataforma interna) e o Pb (plataforma externa) apresentaram uma fração da matéria orgânica importante. O Mo apresentou uma fração pirítica mais importante. O fracionamento geoquímico demonstrou que as formas nas quais os elementos foram acumulados, indicam fortemente influência da diagênese sedimentar. As concentrações de Fe e de S pirítico não foram fatores limitantes no grau de piritização dos elementos-traço. A associação de elementos-traço, tanto à fração ligada à MO quanto à fração ligada à pirita, contribuiu para determinar a retenção de elementos nos sedimentos. Quanto mais intensos foram os processos de re-oxidação do ciclo do S (indicados pela assinatura isotópica da pirita, δ34S), maior foi o grau de piritização do Pb, ao contrário do encontrado para Fe, Cu e Mo, em áreas específicas da plataforma. A estabilização do nível do mar foi o principal evento paleo-oceanográfico determinando a variação vertical da acumulação nos últimos 8.000 anos cal AP, sendo que a variabilidade dos fluxos dos elementos estudados (em relação ao somatório das frações não-detríticas obtidas na extração sequencial) não tendeu a acompanhar a variabilidade do fracionamento geoquímico. Mesmo sob condições oxidantes da coluna d’água, pode ser encontrado um sinergismo da associação à MO e à pirita, contribuindo para determinar a retenção de elementos como Cd, Co, Cu, Mo e Pb nos sedimentos / The accumulation of trace elements in the sediments plays an important role in the cycling of these elements in marine environments, associated with different forms of retention in the sedimentary reservoir, at different time scales. In the present study, the geochemical fractionation of Fe, Mn, As, Cd, Co, Cr, Cu, Mo, Ni, Pb and Zn was evaluated between the fractions soluble in HCl, associated with pyrite (FeS2) and associated with the organic fraction, To elucidate the processes that determine the accumulation of these elements in sediments of the continental shelf of the Cabo Frio Upwelling System (CFUS) in the last 8,000 years. It was observed that the fractionation of the elements Fe, Mn, As, Cr, Ni, Pb and Zn presents a higher proportion in the soluble fraction in HCl in the three sediment cores collected along the continental shelf. Cu in all seasons presented a higher proportion in the fraction of organic matter. The Cd (inner shelf) and the Pb (outer shelf) presented a fraction of the important organic matter. Mo presented a more important pyritic fraction. Geochemical fractionation has shown that the forms in which the elements are being accumulated are strongly influenced by sedimentary diagenesis. The concentrations of Fe and S pyritic were not limiting factors in the degree of piritization of trace elements. The association of trace elements to the fraction bound to the MO and to the fraction bound to pyrite contributed to determine the retention of elements in the sediments. The more intense the S-cycle re-oxidation processes (indicated by the isotopic signature of pyrite, δ34S), the higher the Pb pyritization degree, as opposed to Fe, Cu and Mo, in specific areas of the shelf. The stabilization of the sea level was the main paleo-oceanographic event determining the vertical variation of the accumulation in the last 8,000 years BP. The variability of the fluxes of the elements studied (in relation to the sum of the non-detrital fractions obtained in the sequential extraction) did not tend to follow the variability of the geochemical fractionation. Even under oxidizing conditions of the water column, a synergism of the association with OM and pyrite can be found, contributing to determine the retention of elements such as Cd, Co, Cu, Mo and Pb in the sediments

Le Système d’Upwelling Péruvien (PUS) et la Zone à Oxygène minimum (OMZ) qui y est associée font partie des régions les plus marquées par les variations climatiques de type El Niño Southern Oscillation (ENSO), tant à l’échelle interannuelle qu’à l’échelle décennale. Or, peu d’enregistrements de l’impact de l’ENSO sur cette zone géographique atteignent ces résolutions temporelles, malgré des conditions propices à la conservation de dépôts sédimentaires laminés.Nous avons analysé ces archives sédimentaires à l’échelle de la lamine et en utilisant des marqueurs sédimentologiques, micro paléontologiques et géochimiques afin de retracer les variations de tous les paramètres susceptibles de répondre aux changements climatiques(précipitations, productivité, dénitrification, températures océaniques de surface). Cette approche nous a permis de disposer d’un enregistrement complet des conditions environnementales dans l’OMZ du Pérou à des échelles pluri-annuelle à multidécennale, ce qui est inégalé sur des périodes au-delà du dernier millénaire. Nous avons ainsi pu mettre en évidence une forte empreinte de la circulation de Walker sur le PUS. Cet impact est modulé par les régions extra tropicales de l’hémisphère Nord, en particulier par l’Oscillation Nord-Atlantique (NAO) à l’échelle multidécennale, par la circulation thermohaline à l’échelle centennale et par l’Anticyclone Sibérien à l’échelle millénaire. / The Peruvian Upwelling System (PUS) and the corresponding Oxygen Minimum Zone (OMZ) are part of the regions where the imprint of climatic variations due to El Niño Southern Oscillation (ENSO) at the interannual and multidecadal timescales is the strongest. However,only a few records of ENSO-like climatic variability reach such short timescales in thisgeographical area, despite prevailing conditions favorable to the preservation of laminatedsediments. We analyzed these sedimentary archives at the scale of the lamination, using sedimentology, micropaleontology and geochemistry. The aim was to trace variations in all parameters responding to climatic changes (rainfall, productivity, denitrification, sea surfacetemperatures). This approach has provided a full record of environmental conditions in thePeruvian OMZ at multiannual and multidecadal timescales for the first time on time intervals exceeding the last millennium. We thus evidenced a strong imprint of the Walker circulation on the PUS. This impact is paced by the extratropical northern hemisphere, especially by the North Atlantic Oscillation (NAO) at the multidecadal timescale, by the thermohaline circulation at the centennial timescale and by the Siberian High at the millennial timescale.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-04-13T15:18:33Z No. of bitstreams: 1 Mestrado Manuel Moreira.pdf: 7413069 bytes, checksum: 0f15055b235c438ffd4fac6dde85f099 (MD5) / Made available in DSpace on 2016-04-13T15:18:33Z (GMT). No. of bitstreams: 1 Mestrado Manuel Moreira.pdf: 7413069 bytes, checksum: 0f15055b235c438ffd4fac6dde85f099 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências-Geoquímica. Niterói, RJ / Elementos-tarços são freqüentemente utilizados como indicadores das condições redox e da paleoprodutividade marinha, que podem afetar a distribuição e o fracionamento geoquímico destes elementos. O potencial efeito do ciclo re-oxidativo da pirita sedimentar sobre o grau de piritização destes indicadores (degree of trace metal pyritization – DTMP) não tem sido anteriormente avaliado. Esta avaliação foi realizada em testemunhos sedimentares da plataforma continental sob influência do Sistema de Ressurgência de Cabo Frio (RJ). A relação do DTMP com a assinatura isotópica do S na pirita (δ34S), que se torna mais leve em resposta ao ciclo re-oxidativo da pirita na área de estudo, sugere que a influência pode ser alta (para Pb, As, Cd e Mn), baixa (para Zn e Cu) ou desprezível (para Cr e Ni), dependendo do elemento considerado. Sedimentos mais antigos e ricos em pirita possibilitaram a identificação de um aparente limiar para o efeito da re-oxidação, após o qual os elementos Pb, As, Cd, Mn e Zn apresentaram maior piritização. Um testemunho em posição intermediária na plataforma apresentou correlações negativas das concentrações reativas de Mn, Cu, Ni e Pb com as concentrações de Fe na pirita, assim como outros dois testemunhos apresentaram em relação a Mn e Pb. Isto sugere um consumo de óxidos de Mn (e metais associados) em reação com a pirita, contribuindo para explicar o alto DTMP apresentado pelo Pb, que discorda das predições termodinâmicas e de cinética de incorporação deste metal pela pirita. As assinaturas isotópicas da pirita na área de estudo (que apresenta condições óxicas), foram semelhantes às de ambientes sedimentares anóxicos e euxínicos reportadas na literatura, sugerindo que o ciclo re-oxidativo pode afetar a susceptibilidade de incorporação e a preservação dos elementos na pirita em uma ampla variedade de condições sedimentares. A abordagem metodológica proposta pode subsidiar a melhor interpretação do processo de piritização e suas aplicações para a indicação de condições paleo-redox e de paleo-produtividade / Potential effects of sedimentary pyrite re-oxidative cycling on the degree of trace metals pyritization (DTMP) were evaluated in four sediment cores from the continental shelf under the influence of a tropical upwelling system (Cabo Frio, Brazil). The DTMP relation with stable isotope signals (δ34S) of chromium reducible sulfur, which became lighter in response to intense pyrite re-oxidative cycling in the study area, suggests high (Pb, As, Cd and Mn), low (Zn and Cu) or negligible (Cr and Ni) re-oxidation influences. Oldest pyrite-richer sediments provide an apparent threshold for intense pyrite re-oxidation, after which most trace elements (Pb, As, Cd, Mn and Zn) presented more accentuated DTMP. A middle shelf core presented negative correlations of reactive Mn, Cu, Ni and Pb with pyrite iron, suggesting Mn oxide (and associated metals) depletion in reaction with pyrite. This contributes to explain the observed high degree of Pb pyritization in disagreement with predictions derived from both thermodynamics and water exchange reaction kinetics. Pyrite δ34S signatures under the oxic bottom water from the study area were similar to those from euxinic sedimentary environments, suggesting that pyrite re-oxidative cycling can affect trace element susceptibility to be incorporated and preserved into pyrite in a wide range of sedimentary conditions