Continental margin sediments play an important role in marine biogeochemical cycles, partly due to high primary production rates and efficient export of organic matter to sediments in margin environments. This thesis presents studies of solute exchange in fine-grained sediments representative of slope and rise environments, and carbon and nitrogen cycling in sandy sediments dominant in continental shelves worldwide. Results of these studies advance understanding of the role of benthic processes on marine ecosystems. In fine-grained sediments, solute exchange by diffusion, biological mixing and bioirrigation can be quantified using in situ flux chambers with inert tracer additions. Mechanistic models of chamber tracer transport across the seabed indicate that in organic-rich sediments, bioirrigation and mixing dominate over a wide range of bottom water oxygen levels, reflecting the patchiness and versatility of benthic macrofaunal communities. Positive correlations between benthic oxygen and tracer fluxes appear site-specific. Reliable chamber volume estimates derived from mechanistic models reveal that empirical fits to chamber tracer datasets may overestimate chamber volume and benthic solute fluxes. The biogeochemistry of sandy, highly permeable sediments that dominate continental shelves is largely unknown because of the difficulty in sampling and studying them under natural conditions. Novel sediment reactors were developed and used to mimic in situ porewater advection and natural sedimentary conditions. Compositional changes of natural seawater, with and without the addition of

Understanding the interactions between ocean and atmosphere in regions of oceanographic fronts is of vital importance for the improvement of numerical models for weather and climate forecasting. In the South Atlantic Ocean (SAO) the meeting between the warm waters of the Brazil Current (BC) and the cold waters of the Malvinas (Falkland) Current (MC) in the region known as the Brazil-Malvinas Confluence (BMC), results in intense mesoscale oceanic activity and, for this reason, this region is considered one of the most energetic of the Global Ocean. The interactions resulting from the thermal contrast in regions oceanographic fronts of the OAS are investigated in this work through estimates of heat fluxes based on data collected in situ and by satellite. The results of this study show that the response to the thermal contrasts found in the ocean is in the form of heat fluxes and these fluxes are critical in modulating the atmospheric boundary layer (ABL). Estimation based on data collected in situ show that in the warm side (north) of the oceanographic front the fluxes are more intense (latent heat: 62 W/m² and sensible heat: 0.6 W/m²) than in the cold side (south) (latent heat: 5.8 W/m² and sensible heat: -13.8 W/m²). In the South Atlantic Current (SAC) along the 30° S parallel, heat fluxes are directly related to the meandering characteristic of the current. The data collected in situ, in addition to allow heat flux estimates at a better spatial resolution, were used to develop a new method for estimating the heat energy exchanged between the atmosphere and the ocean caused by the presence of mesoscale oceanic structures. This methodology consists in the comparison of a radiosonde profile taken over waters of the structure of interest and another taken over waters which do not belong to this structure. The methodology was used to estimate the heat energy transfer between the atmosphere and the ocean over the top of three structures sampled in the OAS. The estimation of the heat energy transferred by a warm eddy detached from the BC points to an energy in the latent (sensible) form of 1.6 1017 J (-2.8 1016 J) which corresponds to approximately 0.011 % of the total heat energy of the eddy transferred to the atmosphere during the field experiment and 0.78 % transferred during the supposed lifetime of the eddy (3 months). Along the CSA two oceanic structures were studied: (i) a cold meander that receives from the atmosphere energy in the latent (sensible) form of 1.4 106 J/m2 (5.4 105 J/m2), and (ii) warmer waters associated with a detached eddy from the Agulhas Current (AC) that transfer to the atmosphe heat energy of approximately 4 106 J/m2 an 5.7 106 J/m2 in the latent and sensible forms, respectively. The estimation of heat energy transfer on top of mesoscale oceanic structures clearly demonstrate the importance of these structures for the heat exchanges between the ocean and the atmosphere and must be taken into account in future works about this subject in the SAO. / A compreensão das interações entre oceano e atmosfera em regiões de frentes oceanográficas é de vital importância para o melhoramento de modelos numéricos de previsão do tempo e clima. No Oceano Atlântico Sul (OAS) o encontro entre as águas quentes da Corrente do Brasil (CB) com as águas frias da Corrente das Malvinas (CM), na região denominada Confluência Brasil-Malvinas (CBM), resulta em intensa atividade oceânica de mesoescala e, por esse motivo, essa região é considerada uma das mais energéticas do Oceano Global. As interações resultantes do contraste termal ao longo de regiões de frentes oceanográficas no OAS são investigadas neste trabalho através de estimativas de fluxos de calor baseadas em dados de satélite e dados coletados in situ. Os resultados do trabalho demonstram que a resposta aos contrastes termais encontrados no oceano se dá na forma de fluxos de calor e que esses fluxos são fundamentais na modulação da Camada Limite Atmosférica (CLA). As estimativas com base em dados coletados in situ demonstram que no lado quente (norte) da frente oceanográfica os fluxos são mais intensos (calor latente: 62 W/m² e calor sensível: 0,6 W/m²) que nos lado frio (sul) (calor latente: 5,8 W/m² e calor sensível: -13,8 W/m²). Na Corrente Sul Atlântica (CSA), ao longo do paralelo de 30° S, os fluxos de calor estão diretamente relacionados a característica meandrante da corrente. Os dados coletados in situ, além de possibilitarem estimativas de fluxo de calor com uma melhor resolução espacial, foram usados no desenvolvimento de uma nova metodologia para estimativa da energia calorífica trocada entre oceano e atmosfera em virtude da presença de estruturas oceânicas de mesoescala. Essa metodologia consiste na comparação entre um perfil de radiossonda tomado sobre águas da estrutura de interesse e outro tomado sobre águas que não pertencem a essa estrutura. A metodologia desenvolvida foi utilizada para determinar a transferência de energia calorífica entre oceano e atmosfera em três estruturas amostradas no OAS. A estimativa da energia calorífica transferida por um vórtice quente desprendido da CB aponta para uma energia na forma latente (sensível) de 1,6 1017 J (-2,8 1016 J) que corresponde a aproximadamente 0,011 % da energia calorífica total do vórtice transferida durante o experimento de campo e de 0,78 % da energia do vórtice transferidos durante o tempo suposto de vida do vórtice (3 meses). Ao longo da CSA, duas estruturas oceânicas foram estudadas: (i) um meandro frio que recebe da atmosfera uma energia na forma latente (sensível) de 1,4 106 J/m2 (5,4 105 J/m2) e (ii) águas mais quentes associadas a um vórtice desprendido da Corrente das Agulhas (CA) que transferem para a atmosfera uma energia calorífica de aproximadamente 4 106 J/m2 e 5,7 106 J/m2 nas formas latente e sensível, respectivamente. As estimativas da transferência de energia calorífica sobre estruturas oceânicas de mesoescala demonstram claramente a importância destas nas trocas de calor entre o oceano e a atmosfera e devem ser levadas em consideração em trabalhos futuros sobre o tema no OAS.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This study investigates the crustal structure, and assesses the qualitative and quantitative impacts of crust-mantle dynamics on subsidence pattern, past and present-day thermal field and petroleum system evolution at the southern South African continental margin through the application of a multi-disciplinary and multi-scale geo-modelling procedure involving both conceptual and numerical approaches. The modelling procedure becomes particularly important as this margin documents a complex interaction of extension and strike-slip tectonics during its Mesozoic continental rifting processes. Located on the southern shelf of South Africa, the Western Bredasdorp Basin (WBB) constitutes the focus of this study and represents the western section of the larger Bredasdorp sub-basin, which is the westernmost of the southern offshore sub-basins. To understand the margin with respect to its present-day structure, isostatic state and thermal field, a combined approach of isostatic, 3D gravity and 3D thermal modelling was performed by integrating potential field, seismic and well data. Complimenting the resulting configuration and thermal field of the latter by measured present-day temperature, vitrinite reflectance and source potential data, basin-scale burial and thermal history and timing of source rock maturation, petroleum generation, expulsion, migration and accumulation were forwardly simulated using a 3D basin modelling technique. This hierarchical modelling workflow enables geologic assumptions and their associated uncertainties to be well constrained and better quantified, particularly in three dimensions. At present-day, the deep crust of the WBB is characterised by a tripartite density structure (i.e. prerift metasediments underlain by upper and lower crustal domains) depicting a strong thinning that is restricted to a narrow E-W striking zone. The configuration of the radiogenic crystalline crust as well as the conductivity contrasts between the deep crust and the shallow sedimentary cover significantly control the present-day thermal field of the study area. In all respects, this present-day configuration reflects typical characteristics of basin evolution in a strike-slip setting. For instance, the orientations of the deep crust and fault-controlled basin-fill are spatially inconsistent, thereby indicating different extension kinematics typical of transtensional pull-apart mechanisms. As such, syn-rift subsidence is quite rapid and short-lived, and isostatic equilibrium is not achieved, particularly at the Moho level. Accompanied syn-rift rapid subsidence and a heat flow peak led to petroleum preservation in the basin since the Early Cretaceous. Two additional post-rift thermal anomalies related to the Late Cretaceous hotspot mechanism and Miocene margin uplift in Southern Africa succeeded the syn-rift control on maturation. This thermal maturity of the five mature source rocks culminated in four main generation and three main accumulation phases which characterise the total petroleum systems of the WBB. The Campanian, Eocene and Miocene uplift scenarios episodically halted source maturation and caused tertiary migration of previously trapped petroleum. Petroleum loss related to the spill point of each trap configuration additionally occurs during the Late Cretaceous-Paleocene and Oligocene-Early Miocene. The timing and extent of migration dynamics are most sensitive to the geological scenario that combined faulting, intrusive seal bypass system and facies heterogeneity. In fact, for models that do not incorporate facies heterogeneity, predicted past and present-day seafloor leakage of petroleum is largely underestimated. This complex interplay of generation and migration mechanisms has significant implications for charging of petroleum accumulations by multiple source rocks. Due to early maturation and late stage tertiary migration, the syn-rift source rocks particularly Mid Hauterivian and Late Hauterivian source intervals significantly control the extent of petroleum accumulation and loss in the basin. Lastly, the modelled 3D crustal configuration and Mezosoic to Cenozoic thermal regime of the WBB dispute classic uniform lithospheric stretching for the southern South African continental margin. Rather, this PhD thesis confirms that differential thinning of the lithosphere related to a transtensional pull-apart mechanism is the most appropriate for accurately predicting the evolution of basin and petroleum systems of the margin. Also, the presented 3D models currently represent the most advanced insights, and thus have clear implications for assessing associated risks in basin and prospect evaluation of the margin as well as other similar continental margins around the world. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die korsstruktuur en evalueer die kwalitatiewe en kwantitatiewe impakte van kors-mantel-dinamika op insinkingspatroon, die termiese veld en petroleumstels evolusie aan die suidelike Suid-Afrikaanse kontinentale grens, in die hede en die verlede, deur die toepassing van ’n multidissiplinêre en multiskaal-geomodelleringsprosedure wat beide konseptuele en numeriese benaderings behels. Die modelleringsprosedure veral is belangrik aangesien hierdie kontinentale grens ’n komplekse interaksie van uitbreidings- en strekkingsparallelle tektoniek gedurende die Mesosoïese vastelandskeurprosesse daarvan dokumenteer. Omdat dit op die suidelike platvorm van Suid-Afrika geleë is, maak die Westelike Bredasdorp Kom (WBK) die fokus van hierdie studie uit, en verteenwoordig dit die westelike deel van die groter Bredasdrop-subkom, wat die verste wes is van die suidelike aflandige subkomme. Om die grens met betrekking tot sy huidige struktuur, isostatiese staat en termiese veld te verstaan, is ’n kombinasie benadering bestaande uit isostatiese, 3D-gravitasie- en 3D- termiese modellering gebruik deur potensiëleveld-, seismiese en boorgatdata te integreer Ondersteunend totot die gevolglike konfigurasie en termiese veld van die laasgenoemde deur middel van hedendaagse temperatuur, soos gemeet, vitriniet-refleksiekoëffisiënt en bronpotensiaal data, komskaal-begrawing en termiese geskiedenis en tydsberekening van brongesteentematurasie, is petroleumgenerasie, -uitwerping, -migrasie en -akkumulasie in die toekoms gesimuleer deur gebruik te maak van ’n 3D-kommodelleringstegniek. Hierdie hierargiese modelleringswerkvloei maak dit moontlik om geologiese aannames en hulle geassosieerde onsekerhede goed aan bande te lê en beter te kwantifiseer, veral in drie dimensies. In die hede word die diep kors van die WBK gekarakteriseer deur ’n drieledige digtheidstruktuur (met ander woorde voorrift-metasedimente onderlê deur bo- en benedekors domeine) wat dui op ’n baie wesenlike verdunning, beperk tot ’n dun O-W-strekkingsone. Die konfigurasie van die radiogeniese kristallyne kors, sowel as die konduktiwiteitskontraste tussen die diep kors en die vlak sedimentêre dekking, beheer grotendeels die hedendaagse termiese veld van die studiearea. Hierdie hedendaagse konfigurasie weerspieël in alle opsigte tipiese eienskappe van kom-evolusie in ’n skuifskeur omgewing. Byvoorbeeld, Die oriëntasies van die diep kors en verskuiwingbeheerde komsedimentasie byvoorbeeld is ruimtelik inkonsekwent en dui daardeur op verskillende ekstensiekinematika, tipies van transtensionale tensiemeganisme. As sulks, is sin-rift-versakking taamlik vinnig en kortstondig, en word isostatiese ekwilibrium nie by die Moho-vlak, in die besonder, bereik nie. Samehangende sin-rift vinnige versakking en hittevloeihoogtepunt het gelei tot petroleum behoud in die kom sedert die vroeë Kryt. Twee bykomende post-rift termiese anomalieë wat verband hou met die laat Kryt-“hotspot” meganisme en die Mioseense kontinentale grensopheffing in Suidelike Afrika het die sin-rift-beheer met maturasie opgevolg. Hierdie termiese maturiteit van die vyf gematureerde brongesteentes het in vier hoofgenerasie- en drie hoofakkumulasie fases, wat die totaliteit van die petroleumstelsels van die WBK karakteriseer, gekulmineer. Die Campaniese, Eoseense en Mioseense opheffings senarios het episodies bronmaturasie gestop en tersiêre migrasie van petroleum wat vroeër opgevang was veroorsaak. Addisioneel vind petroleumverlies gekoppel aan die spilpunt van elke opvanggebiedkonfigurasie tydens die laat Kryt-Paleoseen en Oligoseenvroeë Mioseen plaas. Die tydstelling en omvang van migrasiedinamika is die sensitiefste vir die geologiese scenario wat verskuiwing, seëlomseilingstelsel en fasiesheterogeniteit kombineer. Trouens, vir modelle wat nie fasiesheterogeniteit inkorporeer nie, is voorspellings van vroeëre en huidige seebodemlekkasie van petroleum grotendeels onderskattings. Hierdie komplekse wisselwerking van generasie- en migrasiemeganismes het beduidende implikasies vir die laai van petroleumakkumulasies deur veelvoudige brongesteentes. Vanweë vroeë maturasie en laatstadiumtersiêre migrasie, oefen die sin-rift-brongesteentes, veral middel Hauterivium- en laat Hauteriviumbronintervalle, beduidende beheer oor die omvang van petroleumakkumulasie en -verlies in die kom uit. Laastens weerspreek die gemodelleerde 3D-korskonfigurasie en Mesosoïese-tot-Senosoïesetermiese regime van die WBK ’n klassieke uniforme litosferiese rekking vir die suidelike Suid- Afrikaanse kontinentale grens. Inteendeel, hierdie PhD-proefskrif bevestig dat ’n differensiële verdunning van die litosfeer, gekoppel aan ’n transtensiemeganisme, die beste geskik is om ’n akkurate voorspelling oor die evolusie van kom- en petroleumstelsels van die kontinentale grens mee te maak. Verder, verteenwoordig die 3D-modelle, wat hier aangebied word, tans die mees gevorderde insigte, en het hierdie modelle dus duidelike implikasies vir die assessering van verwante risiko’s in kom- en petroleum teikene valuering van die kontinentale grens, so wel as van ander soortgelyke kontinentale grense regoor die wêreld.

The intrusion pathways and physical mechanisms associated with intrusions of cold, nutrient-rich South Atlantic Central Water (SACW) onto the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S-22°S), are investigated. The approach consists of analyses of a set of simplified, process-oriented, primitive-equation numerical models supported by the analyses of an independent, more realistic numerical model and available observations. The cross-isobath circulation is found to be strongly dominated by wind-driving, consistent with previous findings. In the model experiments, SACW enters the ESB shelf through two preferential pathways along the Tubarão Bight area (TB, 19.5°S-22°S). These pathways are found to be locations where an equatorward along-isobath pressure gradient force (PGFy∗) of ∼2 x 10-6 m s-2 develops in response to steady wind forcing. This equatorward PGFy∗ is essentially in geostrophic balance, and therefore induces onshore flow across the shelf edge and most of the shelf proper. The Brazil Current (BC) imparts an additional equatorward PGFy∗ on the shelf. The momentum budget reveals that the ageostrophic residue of the PGFy∗ is compensated mostly by momentum advection and bottom friction. Buoyancy arrest might be important under more intense SACW intrusion events, as suggested by the maximum observed values of the slope Burger number (0.32-0.92). Among the deep ocean forcing mechanisms considered, the intrinsic pycnocline uplifting effect of the BC seems to be responsible for ∼1.4°C colder upwelled water under steady, upwelling-favorable wind forcing, relative to a flat stratification scenario. The BC also seems to induce local intrusions by inertially overshooting the shelf edge, consistent with Rossby numbers of ∼0.3-0.5, as estimated for the area along the TB shelf edge. Finally, the planetary β-effect is also related to a background equatorward PGFy∗. In addition, the steady response of the continental shelf to a periodic (in the along-shelf direction) pressure forcing at the shelf edge is compared with the BC-forced primitive-equation numerical solutions. A simple Arrested Topographic Wave (ATW) analytical model is found to be successful in representing the general features of the numerical solutions. The cross-shelf e-folding scales of the cross-shelf velocity estimated from the numerical solutions agree in order of magnitude with the cross-shelf penetration scale q-1 = [-2r/(lfs)]½ = 10 km predicted by the ATW, where r is a linear bottom resistance parameter, l is the along-shelf wavenumber of the forcing at the shelf edge, f is the Coriolis parameter and s is the bottom slope. Furthermore, the use of quadratic bottom stress accounts for some of the relative increase in the numerical onshore penetration scales, which are predicted to be qquadratic-1 = [-2CD/(lfs)]½ [Ubot]½, where CD is a quadratic bottom friction parameter and Ubot is the near-bottom velocity magnitude. The kind of steady response to periodic deep ocean forcing examined here may provide insight into other continental shelves under the influence of western boundary currents. / Os caminhos e os mecanismos físicos associados ao fenômeno de intrusão da Água Central do Atlântico Sul (ACAS) na plataforma continental da Bacia do Espírito Santo (BES) ao largo da costa sudeste (18°S-22°S) são investigados nesta dissertação. A abordagem consiste da análise de experimentos numéricos de equações primitivas simplificados, combinados com a análise de um modelo numérico mais completo, e com análise de observações disponíveis. Conclui-se que a circulação na direção perpendicular às isóbatas é fortemente dominada pelo vento, de acordo com resultados pretéritos. Nos experimentos numéricos, a ACAS ingressa na plataforma da BES através de dois caminhos preferenciais de intrusão no Embaiamento de Tubarão (ET, 19,5°S-22°S). Estes caminhos de intrusão coincidem com áreas em que uma Força do Gradiente de Pressão na direção paralela às isóbatas (PGFy∗), com magnitude de ∼2 x 10-6 m s-2, se forma em resposta ao vento. A PGFy∗ se encontra essencialmente em balanço geostrófico, e impulsiona um escoamento na direção da costa. A Corrente do Brasil (CB) induz uma PGFy∗ adicional favorável à intrusão. O balanço de momentum revela que o resíduo ageostrófico da PGFy∗ é balanceado principalmente pela advecção de momentum e pelo atrito de fundo. O mecanismo de desligamento da camada de Ekman de fundo por empuxo (tradução livre de buoyancy arrest) pode ser importante em eventos mais intensos de intrusão de ACAS, em razão das estimativas do número de Burger de inclinação (tradução livre de slope Burger number) observado (0,32-0,92). O efeito de soerguimento da termoclina ligado à CB aparenta diminuir em ∼1,4 °C a temperatura da água que aflora em eventos de ressurgência costeira. A CB também parece produzir intrusões locais na borda da plataforma por efeitos inerciais, de acordo com as estimativas de ∼0,3-0,5 para o número de Rossby ao longo da borda da plataforma. Por fim, o efeito β planetário também é associado a uma PGFy∗ básica na direção do equador. Adicionalmente, a resposta estacionária da plataforma continental a um campo de pressão periódico ao longo da borda da plataforma é comparada com as soluções numéricas. Um simples modelo analítico do tipo Onda Topográfica Aprisionada (OTA, tradução livre de Arrested Topographic Wave) representa as características gerais das soluções numéricas. As escalas de decaimento Neperiano (e) na direção perpendicular à plataforma estimadas a partir das soluções numéricas são comparáveis à escala de penetração q-1 = [-2r/(lfs)]½ = 10 km prevista pela OTA, onde r é um coeficiente linear de atrito de fundo, l é o número de onda da forçante, f é o parâmetro de Coriolis e s é a inclinação do fundo. O uso de uma parametrização quadrática para o atrito de fundo prevê parte da diminuição da e. A escala de penetração quadrática é qquadratic-1 = [-2CD/(lfs)]½[Ubot]½, onde CD é um coeficiente quadrático de atrito de fundo e Ubot é a magnitude da velocidade próxima ao fundo. Este tipo de resposta estacionária da plataforma a uma forçante periódica ligada ao oceano profundo pode ajudar a elucidar processos físicos em outras plataformas continentais que se encontram sob a influência de correntes de limite oeste.

O objetivo do presente estudo é avaliar o uso associado dos proxies ?18O e Mg/Ca obtidos em testas de foraminíferos. Para alcançar tal objetivo foram realizadas análises de ?18O e Elemento/Ca em amostras de foraminíferos planctônicos (G. ruber e G. sacculifer) e bentônicos (Cibicidoides spp., C. corpulentus, Uvigerina spp. e H. elegans) de dois testemunhos do Atlântico Sul. Os resultados demonstraram que apesar dos proxies ?18O e Mg/Ca apresentarem perfis distintos em relação às espécies os mesmos se correlacionam de forma apropriada, sendo possível estimar a temperatura e os sinais de ?18OSW e ?18OLocal a partir dos mesmos. A partir dos dados de temperatura estimados com base em Mg/Ca foi possível identificar uma anomalia negativa das águas superficias entre o LGM e o HL de -1,5 ± 0,2 °C, enquanto que nas águas profundas observou-se uma anomali positiva de 1,7 ± 0,4 °C para o mesmo período. Os dados de ?18OSW estimados com base nos dados de temperatura e ?18O indicaram uma oscilação de 1,0 ± 0,1 ? e 2,0 ± 0,2 ? para as espécies planctônicas e bentônicas durante o LGM e o HL. Segundo o valor esperado para a variação do volume de gelo (~1,2 ?) há uma oscilação muito baixa da salinidade nas águas superficias da região de estudo, em contraste com uma oscilação bem marcada da salinidade nas águas de fundo. As estimativas de ?18OLocal indicaram uma oscilação entre o LGM e o HL muito pequena da salinidade (~0,1 ?) nas águas superficiais, com uma oscilação maior nas águas de fundo (1,0 ± 0,3 ?). O aumento da salinidade das águas de fundo durante o LGM corrobora a anomalia positiva da temperatura observada neste estudo, visto que, para a ocorrência da mesma, é necessário que a densidade das águas de fundo seja suficiente para manter a estratificação da coluna de água. / The goal of this study is to evaluate the associated use of the proxies ?18O and Mg/Ca, both analyzed in foraminifera tests. ?18O and trace metals analyses were performed in order to achieve this purpose on samples of planktonic (G. ruber and G. sacculifer) and benthic (Cibicidoides spp., C. corpulentus, Uvigerina spp. and H. elegans) species of foraminifera from two cores from South Atlantic. Despite of the fact that the proxies used on this study present distinct fits within the species they correlate very well, being possible to estimate the values of temperature, ?18OSW and ?18OLocal. Based on the temperature estimated by Mg/Ca it was possible to identify a negative anomaly of -1,5 ± 0,2 °C between the LGM and HL, meanwhile a positive anomaly of 1,7 ± 0,4 °C was observed in the deep waters for the same period. The ?18OSW data estimated by temperature and ?18O indicate an oscilation of 1,0 ± 0,1 ? and 2,0 ± 0,2 ? for planktonic and benthic species between the LGM and the HL. Based on the literature value for the ice volume signal (~1,2 ?) the superficial waters of the study area indicated a very low salinity oscilation, opposite to the high salinity oscillation in the deep waters. The ?18OLocal estimatives exhibited a very weak salinity oscillation between LGM and HL in the superficial waters (~0,1 ?), providing a much more strong oscilation in the deep waters (1,0 ± 0,3 ?). The salinity increase during the LGM in the deep waters establish the validity of the positive temperature anomaly observed in this study, since the density of the deep water needs to be adequate to maintain the water column stratification.

The intrusion pathways and physical mechanisms associated with intrusions of cold, nutrient-rich South Atlantic Central Water (SACW) onto the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S-22°S), are investigated. The approach consists of analyses of a set of simplified, process-oriented, primitive-equation numerical models supported by the analyses of an independent, more realistic numerical model and available observations. The cross-isobath circulation is found to be strongly dominated by wind-driving, consistent with previous findings. In the model experiments, SACW enters the ESB shelf through two preferential pathways along the Tubarão Bight area (TB, 19.5°S-22°S). These pathways are found to be locations where an equatorward along-isobath pressure gradient force (PGFy∗) of ∼2 x 10-6 m s-2 develops in response to steady wind forcing. This equatorward PGFy∗ is essentially in geostrophic balance, and therefore induces onshore flow across the shelf edge and most of the shelf proper. The Brazil Current (BC) imparts an additional equatorward PGFy∗ on the shelf. The momentum budget reveals that the ageostrophic residue of the PGFy∗ is compensated mostly by momentum advection and bottom friction. Buoyancy arrest might be important under more intense SACW intrusion events, as suggested by the maximum observed values of the slope Burger number (0.32-0.92). Among the deep ocean forcing mechanisms considered, the intrinsic pycnocline uplifting effect of the BC seems to be responsible for ∼1.4°C colder upwelled water under steady, upwelling-favorable wind forcing, relative to a flat stratification scenario. The BC also seems to induce local intrusions by inertially overshooting the shelf edge, consistent with Rossby numbers of ∼0.3-0.5, as estimated for the area along the TB shelf edge. Finally, the planetary β-effect is also related to a background equatorward PGFy∗. In addition, the steady response of the continental shelf to a periodic (in the along-shelf direction) pressure forcing at the shelf edge is compared with the BC-forced primitive-equation numerical solutions. A simple Arrested Topographic Wave (ATW) analytical model is found to be successful in representing the general features of the numerical solutions. The cross-shelf e-folding scales of the cross-shelf velocity estimated from the numerical solutions agree in order of magnitude with the cross-shelf penetration scale q-1 = [-2r/(lfs)]½ = 10 km predicted by the ATW, where r is a linear bottom resistance parameter, l is the along-shelf wavenumber of the forcing at the shelf edge, f is the Coriolis parameter and s is the bottom slope. Furthermore, the use of quadratic bottom stress accounts for some of the relative increase in the numerical onshore penetration scales, which are predicted to be qquadratic-1 = [-2CD/(lfs)]½ [Ubot]½, where CD is a quadratic bottom friction parameter and Ubot is the near-bottom velocity magnitude. The kind of steady response to periodic deep ocean forcing examined here may provide insight into other continental shelves under the influence of western boundary currents. / Os caminhos e os mecanismos físicos associados ao fenômeno de intrusão da Água Central do Atlântico Sul (ACAS) na plataforma continental da Bacia do Espírito Santo (BES) ao largo da costa sudeste (18°S-22°S) são investigados nesta dissertação. A abordagem consiste da análise de experimentos numéricos de equações primitivas simplificados, combinados com a análise de um modelo numérico mais completo, e com análise de observações disponíveis. Conclui-se que a circulação na direção perpendicular às isóbatas é fortemente dominada pelo vento, de acordo com resultados pretéritos. Nos experimentos numéricos, a ACAS ingressa na plataforma da BES através de dois caminhos preferenciais de intrusão no Embaiamento de Tubarão (ET, 19,5°S-22°S). Estes caminhos de intrusão coincidem com áreas em que uma Força do Gradiente de Pressão na direção paralela às isóbatas (PGFy∗), com magnitude de ∼2 x 10-6 m s-2, se forma em resposta ao vento. A PGFy∗ se encontra essencialmente em balanço geostrófico, e impulsiona um escoamento na direção da costa. A Corrente do Brasil (CB) induz uma PGFy∗ adicional favorável à intrusão. O balanço de momentum revela que o resíduo ageostrófico da PGFy∗ é balanceado principalmente pela advecção de momentum e pelo atrito de fundo. O mecanismo de desligamento da camada de Ekman de fundo por empuxo (tradução livre de buoyancy arrest) pode ser importante em eventos mais intensos de intrusão de ACAS, em razão das estimativas do número de Burger de inclinação (tradução livre de slope Burger number) observado (0,32-0,92). O efeito de soerguimento da termoclina ligado à CB aparenta diminuir em ∼1,4 °C a temperatura da água que aflora em eventos de ressurgência costeira. A CB também parece produzir intrusões locais na borda da plataforma por efeitos inerciais, de acordo com as estimativas de ∼0,3-0,5 para o número de Rossby ao longo da borda da plataforma. Por fim, o efeito β planetário também é associado a uma PGFy∗ básica na direção do equador. Adicionalmente, a resposta estacionária da plataforma continental a um campo de pressão periódico ao longo da borda da plataforma é comparada com as soluções numéricas. Um simples modelo analítico do tipo Onda Topográfica Aprisionada (OTA, tradução livre de Arrested Topographic Wave) representa as características gerais das soluções numéricas. As escalas de decaimento Neperiano (e) na direção perpendicular à plataforma estimadas a partir das soluções numéricas são comparáveis à escala de penetração q-1 = [-2r/(lfs)]½ = 10 km prevista pela OTA, onde r é um coeficiente linear de atrito de fundo, l é o número de onda da forçante, f é o parâmetro de Coriolis e s é a inclinação do fundo. O uso de uma parametrização quadrática para o atrito de fundo prevê parte da diminuição da e. A escala de penetração quadrática é qquadratic-1 = [-2CD/(lfs)]½[Ubot]½, onde CD é um coeficiente quadrático de atrito de fundo e Ubot é a magnitude da velocidade próxima ao fundo. Este tipo de resposta estacionária da plataforma a uma forçante periódica ligada ao oceano profundo pode ajudar a elucidar processos físicos em outras plataformas continentais que se encontram sob a influência de correntes de limite oeste.

O objetivo do presente estudo é avaliar o uso associado dos proxies ?18O e Mg/Ca obtidos em testas de foraminíferos. Para alcançar tal objetivo foram realizadas análises de ?18O e Elemento/Ca em amostras de foraminíferos planctônicos (G. ruber e G. sacculifer) e bentônicos (Cibicidoides spp., C. corpulentus, Uvigerina spp. e H. elegans) de dois testemunhos do Atlântico Sul. Os resultados demonstraram que apesar dos proxies ?18O e Mg/Ca apresentarem perfis distintos em relação às espécies os mesmos se correlacionam de forma apropriada, sendo possível estimar a temperatura e os sinais de ?18OSW e ?18OLocal a partir dos mesmos. A partir dos dados de temperatura estimados com base em Mg/Ca foi possível identificar uma anomalia negativa das águas superficias entre o LGM e o HL de -1,5 ± 0,2 °C, enquanto que nas águas profundas observou-se uma anomali positiva de 1,7 ± 0,4 °C para o mesmo período. Os dados de ?18OSW estimados com base nos dados de temperatura e ?18O indicaram uma oscilação de 1,0 ± 0,1 ? e 2,0 ± 0,2 ? para as espécies planctônicas e bentônicas durante o LGM e o HL. Segundo o valor esperado para a variação do volume de gelo (~1,2 ?) há uma oscilação muito baixa da salinidade nas águas superficias da região de estudo, em contraste com uma oscilação bem marcada da salinidade nas águas de fundo. As estimativas de ?18OLocal indicaram uma oscilação entre o LGM e o HL muito pequena da salinidade (~0,1 ?) nas águas superficiais, com uma oscilação maior nas águas de fundo (1,0 ± 0,3 ?). O aumento da salinidade das águas de fundo durante o LGM corrobora a anomalia positiva da temperatura observada neste estudo, visto que, para a ocorrência da mesma, é necessário que a densidade das águas de fundo seja suficiente para manter a estratificação da coluna de água. / The goal of this study is to evaluate the associated use of the proxies ?18O and Mg/Ca, both analyzed in foraminifera tests. ?18O and trace metals analyses were performed in order to achieve this purpose on samples of planktonic (G. ruber and G. sacculifer) and benthic (Cibicidoides spp., C. corpulentus, Uvigerina spp. and H. elegans) species of foraminifera from two cores from South Atlantic. Despite of the fact that the proxies used on this study present distinct fits within the species they correlate very well, being possible to estimate the values of temperature, ?18OSW and ?18OLocal. Based on the temperature estimated by Mg/Ca it was possible to identify a negative anomaly of -1,5 ± 0,2 °C between the LGM and HL, meanwhile a positive anomaly of 1,7 ± 0,4 °C was observed in the deep waters for the same period. The ?18OSW data estimated by temperature and ?18O indicate an oscilation of 1,0 ± 0,1 ? and 2,0 ± 0,2 ? for planktonic and benthic species between the LGM and the HL. Based on the literature value for the ice volume signal (~1,2 ?) the superficial waters of the study area indicated a very low salinity oscilation, opposite to the high salinity oscillation in the deep waters. The ?18OLocal estimatives exhibited a very weak salinity oscillation between LGM and HL in the superficial waters (~0,1 ?), providing a much more strong oscilation in the deep waters (1,0 ± 0,3 ?). The salinity increase during the LGM in the deep waters establish the validity of the positive temperature anomaly observed in this study, since the density of the deep water needs to be adequate to maintain the water column stratification.

<p dir="ltr">Tropical Cyclones (TCs) are intense low-pressure weather systems that acts as a meteorological monster causing severe rainfall and widespread freshwater flooding, leading to extensive damage and disruption. Quantitative precipitation estimates (QPEs) are crucial for accurately understanding and evaluating the impacts of TCs. However, QPEs derived from various modalities, such as rain gauges, ground-based merged radars, and satellites, can differ significantly and require thorough comparison. Understanding the limitations/advantages of using each QPE is essential to simulate a hydrological model especially to estimate extreme events like TCs. The objective of the dissertation is to 1) characterize the tropical cyclone precipitation (TCP) using three gridded products, 2) characterize the impact of using different QPEs in estimation of hydrological variables using a hydrology model, and 3) understand the usability of satellite-derived QPEs for eight cases of TC and its impact on the estimate of hydrological variables. The QPEs include near real-time and post-processed satellite data from NASA’s Global Precipitation Mission-Integrated Multi-sensor Retrievals for GPM Rainfall Product (IMERG), merged ground radar observations (Stage IV) from the National Centers for Environmental Prediction (NCEP), and interpolated gauge observations from the National Weather Service Cooperative Observer Program (GCOOP). The study quantifies how differences in rainfall intensity and location, as derived from these gridded precipitation datasets, impact surface hydrology. The Variable Infiltration Capacity (VIC) model and the geographic information system (GIS) routing assess the propagation of bias in the daily rainfall rate to total runoff, evapotranspiration, and flooding. The analysis covers eight tropical cyclones, including Hurricane Charley (2004), Hurricane Frances (2004), Hurricane Jeanne (2004), Tropical Storm Fay (2008), Tropical Storm Beryl (2012), Tropical Storm Debby (2012), Hurricane Irma (2017) and Hurricane Michael (2018) focusing on different regions in South-Atlantic Gulf region and land uses. The findings indicate that IMERG underpredicts precipitation at higher quantiles but aligns closely with ground-based and radar-based products at lower quantiles. IMERG reliably estimates total runoff and evapotranspiration in 90% of TC scenarios along the track and in agricultural and forested regions. There is substantial overlap ~ 70% between IMERG and GCOOP/Stage IV for the 90th percentile rainfall spatially for the case of TC Beryl 2012. Despite previous perceptions of underestimation, the study suggests that satellite-derived rainfall products can be valuable in simulating streamflow, particularly in data-scarce regions where ground estimates are lacking. The relative error in estimation is 12% and 22% when using IMERG instead of Stage IV and GCOOP rainfall data. The findings contribute to a broader perspective on usability of IMERG in estimating near real-time hydrological characteristics, paving the way for further research in this area. This analysis demonstrates that IMERG can be a reliable data product for hydrological studies even in the extreme events like landfalling TCs. This will be helpful in improving the preparedness of vulnerable communities and infrastructure against TC-induced flooding in data scare regions.</p>

Denna undersökning har studerat ett lätt infanteriförbands användning av kombinerad bekämpning som metod för verkan under en amfibieoperation samt vilka aspekter som påverkade möjligheten till kombinerad bekämpning p.g.a. operationens amfibiska karaktär. Fallet har utgjorts av Parachute Regiments två bataljoner som under Falklandskriget utkämpade tre slag vid Darwin – Goose Green, Mount Longdon och Wireless Ridge. Som analysverktyg har använts Robert Leonhards teori om den kombinerade bekämpningens tre principer. Indikatorer på principerna har varit syften med verkan hämtade ur teorin om de grundläggande förmågorna. Två av slagen befanns endast delvis kännetecknas av Leonhards två första principer, principerna om kompletterande system och dilemman. Den tredje principen om fördelaktig terräng uppfylldes inte. Det tredje slaget regementet utkämpade kännetecknades helt igenom av Leonhards två första principer medan den tredje delvis beaktades. Undersökningen konstaterar att kombinerad bekämpning som metod för verkan kan utvecklas av ett lätt infanteriförband under en amfibieoperation. Dock ledde ofördelaktig disponering av förbandet i de aktuella fallen till att kombinerad bekämpning tidvis omöjliggjordes. Leonhards tredje princip tenderade att förringas. De specifikt amfibiska aspekterna avseende möjligheten till kombinerad bekämpning utgjordes främst av tillgången till fartygsartilleri, kraven på helikoptertransporterbart fältartilleri samt bristen på lätta trossfordon. / This dissertation has investigated how a light infantry force has used combined arms during an amphibious operation, specific factors related to the operations character affecting the possibility to develop combined arms have also been highlighted. The case chosen for the study was Parachute Regiments actions during the three battles of Darwin – Goose Green, Mount Longdon and Wireless Ridge during the Falklands War. As a analytical tool Robert Leonhard’s theory about the three principles of combined arms was used together with indicators borrowed from the theory about the warfighting functions purposes of fires. Two of the battles were found to be only partially characterized by Leonhard’s first two principles, complementary systems and dilemmas. The third principle about favorable terrain was neglected. The third battle was throughout characterized by the first two principles and to a larger extent than the former by the third principle. The dissertation concludes that light infantry can use combined arms during amphibious operations. The battles studied were, however, often characterized by unfavorable disposition of the force which affected the possibilities to use combined arms. Leonhard´s third principle was usually neglected. The most important amphibious aspects affecting the possibilities to combined arms were found to be naval gunfire support, light field artillery and the scarcity of light all-terrain vehicles.