Dissertations / Theses on the topic 'Atlantic Waters'

Generalised additive models (GAMs) were used on data for <I>L. forbesii </I>in northeast Atlantic waters to analyse patterns of reproductive and somatic investment.&nbsp; Geographic variation in the relationships, seen between Scottish males and samples from other study areas, is hypothesised to be largely attributable to local differences in environmental conditions and demonstrates that <I>L. forbesii </I>growth and maturation is variable in response to both intrinsic and extrinsic factors.&nbsp; GAMs were also applied to trawl survey data to relate squid with ecogeographic variables in order to identify the variability of the habitat preferences of <I>L. forbesii </I>in UK waters.&nbsp; Favourable values for depth, SST, salinity and sediment composition were identified and related to known biological characteristics.&nbsp; Results suggest that habitat preferences may vary from season to season, but are rather consistent across different life cycle stages of the population.&nbsp; Knowledge gained could be used by fishers for more effective species targeting, and by managers as a tool to identify spawning grounds for potential protection.&nbsp; Finally, the recent history of the directed squid fishery in the Moray Firth was reviewed using both fishers’ knowledge and fishery statistics.&nbsp; Peaks in landings and CPUE were experienced during 2003-2005, with a marked decrease in both values in 2006.&nbsp; Fishers reported egg presence during summer months, providing new evidence of summer breeding in this population.&nbsp; Ideas are presented from the fishers’ viewpoints and from a research-based fishery perspective on possible drivers behind the variability in catch, as well as preferred options for future regulatory measures.

The microbial community dominates biogeochemical cycling of the ocean, affecting global climate. The impact of physical disturbance of near surface microbial populations was studied in the northeastern tropical and subtropical Atlantic Ocean. This region lies beneath easterly trade winds, resulting in strong perturbations in terms of wind driven mixing and Aeolian dust deposition. Firstly, the region’s surface water bacterioplankton community was compared with adjacent regions in terms of metabolic activity, by measuring the uptake rates of radioactively labelled amino acids (3H-leucine and 35S-methionine) as a proxy for bacterial production. Remarkably, there was little variation in uptake rates between the two Atlantic (sub-)tropical gyres. Rates reflected regional photosynthetic biomass, except in the study region. The bacterioplankton community of this region was less metabolically active than that of the oligotrophic north Atlantic gyre, despite ocean colour data identifying the region as productive. The region’s uniqueness is probably related to the episodic Saharan dust inputs experienced. To test whether dust deposition controls microbial community structure, surface communities were compared, using flow cytometry and fluorescence in situ hybridisation, between two winter periods when either wind-driven mixing or dust deposition occurred. Wind-driven mixing was associated with domination by the ubiquitous SAR11 clade of Alphaproteobacteria, whereas key primary producers, Prochlorococcus cyanobacteria, numerically dominated during calmer conditions. Phytoplankton-associated Bacteroidetes and Synechococcus cyanobacteria were most abundant during turbulent conditions. Gammaproteobacteria, encompassing opportunistic species, were the only group to benefit from dust inputs; thus dust deposition seems to have a minor influence on the region’s bacterioplankton community compared to wind mixing, suggesting community change following dust storm events may be linked to nutrients delivered by wind mixing, as much as from dust. To test further whether changes in the SAR11 and Prochlorococcus populations varied between years due to wind- or dust-related perturbation, a method based on 35S-methionine uptake was developed for measuring the metabolic response of these groups to Aeolian dust, whilst excluding wind impacts. Subsurface seawater samples were treated with freshly collected dust, added directly or indirectly as a “leachate” after its rapid dissolution in deionised water. Prochlorococcus and SAR11 cells were sorted by flow cytometry to determine their group-specific responses. Both Prochlorococcus and SAR11 were metabolically impaired by the addition of dust, which may explain the low metabolic activity observed in the region (mentioned above). Although SAR11 showed minor positive responses to dust leachate additions, leachate proved detrimental to Prochlorococcus. Thus dust dissolution in situ appears to be more deleterious to Prochlorococcus than SAR11 and hence could initiate a compositional shift in the indigenous bacterioplankton, suggesting the observed switch from SAR11- to Prochlorococcus-domination following dust deposition (mentioned above) was indeed a result of an alternative stimulus, most likely wind stress. In conclusion, whereas dust deposition may prove beneficial to bacterioplankton species with high nutrient demands, such as some Gammaproteobacteria, it does not appear to affect the ambient dominant bacterioplankton groups of the northeast (sub-)tropical Atlantic to the same degree as wind-driven perturbations. Furthermore, large dust deposition events may prove detrimental to ambient populations, resulting in low community metabolic activity.

Doutoramento em Biologia<br>With the aim to provide new insights into operational cetacean-fishery interactions in Atlantic waters, this thesis assesses interactions of cetaceans with Spanish and Portuguese fishing vessels operating in Iberian and South West Atlantic waters. Different opportunistic research methodologies were applied, including an interview survey with fishers (mainly skippers) and onboard observations by fisheries observers and skippers, to describe different types of interactions and to identify potential hotspots for cetacean-fishery interactions and the cetacean species most involved, and to quantify the extent and the consequences of these interactions in terms of benefits and costs for cetaceans and fisheries. In addition, the suitability of different mitigation strategies was evaluated and discussed. The results of this work indicate that cetaceans interact frequently with Spanish and Portuguese fishing vessels, sometimes in a beneficial way (e.g. cetaceans indicate fish schools in purse seine fisheries), but mostly with negative consequences (depredation on catch, gear damage and cetacean bycatch). Significant economic loss and high bycatch rates are, however, only reported for certain fisheries and associated with particular cetacean species. In Galician fisheries, substantial economic loss was reported as a result of bottlenose dolphins damaging artisanal coastal gillnets, while high catch loss may arise from common dolphins scattering fish in purse seine fisheries. High cetacean bycatch mortality arises in trawl fisheries, mainly of common dolphin and particularly during trawling in water depths below 350 m, and in coastal set gillnet fisheries (mainly common and bottlenose dolphins). In large-scale bottom-set longline fisheries in South West Atlantic waters, sperm whales may significantly reduce catch rates through depredation on catch. The high diversity of cetacean-fishery interactions observed in the study area indicates that case-specific management strategies are needed to reduce negative impacts on fisheries and cetaceans. Acoustic deterrent devices (pingers) may be used to prevent small cetaceans from approaching and getting entangled in purse seines and set gillnets, although possible problems include cetacean habituation to the pinger sounds, as well as negative side effects on non-target cetaceans (habitat exclusion) and fisheries target species (reduced catch rates). For sardine and horse mackerel, target species of Iberian Atlantic fisheries, no aversive reaction to pinger sounds was detected during tank experiments conducted in the scope of this thesis. Bycatch in trawls may be reduced by the implementation of time/area restrictions of fishing activity. In addition, the avoidance of fishing areas with high cetacean abundance combined with the minimization of fishery-specific sound cues that possibly attract cetaceans, may also help to decrease interactions. In large-scale bottom-set longline fisheries, cetacean depredation on catch may be reduced by covering hooked fish with net sleeves ("umbrellas") provided that catch rates are not negatively affected by this gear modification. Trap fishing, as an alternative fishing method to bottom-set gillnetting and longlining, also has the potential to reduce cetacean bycatch and depredation, given that fish catch rates are similar to the rates obtained by bottom-set gillnets and longlines, whereas cetacean by-catch is unlikely. Economic incentives, such as the eco-certification of dolphin-safe fishing methods, should be promoted in order to create an additional source of income for fishers negatively affected by interactions with cetaceans, which, in turn, may also increase fishers’ willingness to accept and adopt mitigation measures. Although the opportunistic sampling methods applied in this work have certain restrictions concerning their reliability and precision, the results are consistent with previous studies in the same area. Moreover, they allow for the active participation of fishers that can provide important complementary ecological and technical knowledge required for cetacean management and conservation.<br>Com a finalidade de melhorar a compreensão das interações entre cetáceos e atividades pesqueiras em águas Atlânticas, esta tese analisa as interações entre cetáceos e artes de pesca Portuguesas e Espanholas a operar em águas Ibéricas e do sudoeste Atlântico. Diferentes metodologias oportunistas de investigação foram aplicadas, incluindo entrevistas com pescadores (principalmente capitães de embarcação) e observações a bordo, quer por observadores de pesca ou capitães, com o fim de 1) descrever os diferentes tipos de interações; 2) identificar potenciais hotspots de interações cetáceos-pesca e quais as espécies de cetáceos mais envolvidas; e quantificar a dimensão e consequências destas interações em termos de custos e benefícios, tanto para cetáceos como para as atividades pesqueiras. Mais ainda, a adequabilidade de diferentes estratégias de mitigação destas interações foi avaliada e discutida. Os resultados obtidos neste trabalho indicam que diferentes espécies de cetáceos interagem frequentemente com embarcações de pesca Portuguesas e Espanholas, muitas vezes com consequências positivas (por ex. com os cetáceos frequentemente indicando cardumes durante a pesca de cerco), mas maioritariamente com consequências negativas (predação pelos cetáceos, levando à perda de pescado, danificação dos aparelhos de pesca e capturas acidentais de cetáceos). No entanto, perdas económicas significativas e altas taxas de captura acidental são raramente declaradas, acontecendo apenas com alguns tipos de pesca e com certas espécies de cetáceos. Na Galiza, perdas económicas substanciais podem resultar de danos nas redes fixas artesanais pelo roaz-corvineiro (Tursiops truncatus), bem como importantes reduções das capturas por golfinho-comum (Delphinus delphis) devido à dispersão de cardumes na pesca de cerco. Altas taxas de mortalidade de cetáceos por captura acidental são declaradas na pesca de arrasto, principalmente de golfinho-comum e quando o arrasto é realizado a profundidades menores que 350 m, assim como em pescas de rede de emalhar e tresmalho em zonas costeiras (principalmente de golfinho comum e roaz-corvineiro). Em águas do Sudoeste Atlântico, cachalotes podem reduzir significativamente taxas de captura por predação em pesca comercial de palangre de fundo. A grande diversidade de interações cetáceos-pesca observadas na área de estudo indicam que estratégias de gestão especificas são necessárias para reduzir impactos negativos tanto nas pescas como nos cetáceos. vi Dispositivos de alerta (pingers) poderiam ser usados para prevenir pequenos cetáceos de se aproximarem e ficarem presos nas redes fixas e redes de cerco, sempre que possam ser possam ser excluídas situações de habituação dos cetáceos ao som dos pingers, assim como efeitos negativos em espécies de cetáceos não alvo (como exclusão de habitat) e espécies-alvo de pesca (redução de capturas). Para sardinha e carapau, duas espécies-alvo muito importantes na pesca Ibérica Atlântica, nenhuma reação negativa ao som do pinger foi detectada durante experiências em tanques conduzidas no âmbito desta tese. Capturas acidentais durante pesca de arrasto poderiam ser reduzidas com a implementação de restrições de tempo/área na atividade de pesca. Adicionalmente, a redução de interações pode ser conseguida se as embarcações evitarem áreas de pesca com grande abundância de cetáceos, integrando medidas de minimização de pistas sonoras que possam atrair cetáceos às embarcações. A depredação de cetáceos sobre capturas de palangre de fundo poderia ser reduzida recorrendo ao encapsulamento dos anzóis ("sistema guarda-chuva"), uma vez que as taxas de captura de peixe não são afectadas por esta modificação. A pesca com armadilha, como alternativa à pesca de redes de fundo fixas e de palangre de fundo tem também o potencial de reduzir a depredação e capturas acidentais de cetáceos, se taxas de captura semelhantes forem conseguidas. Incentivos económicos, como a eco-certificação de métodos de pesca não prejudiciais às populações de cetáceos, devem ser promovidos de modo que possam constituir uma fonte adicional de rendimento para pescadores afectados negativamente por estas interações, o que por sua vez poderá também aumentar a disponibilidade dos pescadores em aceitar e adoptar medidas mitigadoras. Apesar dos métodos oportunistas aplicados neste trabalho poderem ter certas restrições no que respeita à precisão e fiabilidade dos dados, os resultados são consistentes com estudos anteriores realizados na mesma área. Mais ainda, eles permitem a participação ativa dos pescadores, que podem aportar conhecimento técnico e ecológico importante necessário para a gestão e conservação de cetáceos.

The sea surface microlayer (SML; depth < 400 μm) is a physically and biogeochemically distinct interface covering the entire ocean surface. Biologically-derived surfactants are ubiquitous in the SML, where they limit air-sea gas exchange and the formation of marine boundary layer aerosols that impact atmospheric chemistry and climate. Total surfactant activity (SA) and chromophoric dissolved organic matter (CDOM) were measured in the SML, in depth profiles (≤ 100 m) and semi-continuously in sub-surface water (SSW: 7 m non-toxic seawater supply) on Atlantic Meridional Transect (AMT) cruises 24 (2014) and 25 (2015), from 50°N to 50°S. On-board estimates of the gas transfer velocity (kw) of CH4 (custom gas exchange tank) were related to SA distributions in the SML to evaluate surfactant control of air-sea gas exchange. SML and SSW SA (mg L-1 eq. T-X-100) was always higher in the Northern Hemisphere than in the Southern Hemisphere (0.10 - 1.76 in the Northern Hemisphere; 0.08 - 0.63 in the Southern Hemisphere). A constant enrichment of SA in the SML was observed at all wind speeds encountered. SA enrichment factors (EF = SASML/SASSW) ranged between 0.95 - 4.25 in the Atlantic Ocean, higher in the Northern Hemisphere than in the Southern Hemisphere. EF >1 up to the maximum mean wind speed recorded (~13 m s-1) challenges the idea that high latitude wind speeds > 12 m s-1 preclude high EFs and implies that the SML is self-sustaining concerning SA. CDOM absorption coefficient (a300) in general was higher in the Northern Hemisphere (range 0.10 - 1.52 m-1) than in the Southern Hemisphere (range 0.17 - 0.82 m-1). CDOM spectral slope (S275-295) showed an inverse correlation with CDOM (a300) and was significantly lower (t-test, p < 0.001) in the SML than in the SSW (SML; 0.033 ± 0.005 nm-1, SSW; 0.038 ± 0.007 nm-1) suggesting in-situ CDOM production in the SML and more refractory CDOM in the SSW. CH4 k660 (kw for CO2 in seawater at 20°C) derived from the gas exchange tank (6.9 - 9.8 cm h-1) gave film factors (R660´; sample kw / surfactant-free MilliQ kw) that strongly correlated with SML SA (r2 = 0.63, p = 0.001, n = 13). Corresponding R660´ suppressions ~ 25% imply a strong control of Atlantic Ocean gas exchange by surfactant.

In 2005, Atlantic salmon (Salmo salar L.) migrating to the United Kingdom exhibited swollen, haemorrhagic vents, symptoms not previously recorded. The condition was latterly termed Red Vent Syndrome (RVS), and subsequently observed across the North Atlantic. RVS has been pathognomonically associated with one of the most abundant parasites within the marine environment, the ascaridoid nematode Anisakis simplex, which also causes Anisakiasis in humans. Although A. simplex is commonly found in Atlantic salmon, heavy infestation of the vent region is novel, and the expression of RVS has not been prevalent in other fish species. Red Vent Syndrome has been well studied, however, the causes of the condition, and the reasons driving the novel site of infestation exhibited by A. simplex, have not been clarified. The aim of this PhD therefore, is to provide new information regarding the underlying factors of the infestation of the vent region by A. simplex, and the emergence of RVS. This study therefore: i) assessed the relationship between nematode burdens within the viscera and musculature, in comparison to the vent in 117 adult Atlantic salmon; ii) compared the genetic structure of A. simplex present in the vent region and the viscera using the entire nuclear internal transcribed spacer (ITS) region; iii) investigated migratory route and feeding ground of Scottish salmon populations using stable isotope analysis of dorsal muscle tissue and parasite component communities and, iv) assessed the expression of the cytokine TNF-α1 within vent muscle tissue using (q)RT-PCR, in relation to RVS severity. Phylogenetic analyses have shown that it is A. simplex sensu stricto infesting the vent region. The results show that there is a significant positive relationship between the nematodue burden in the body (viscera and musculature) and in the vent region. Isotopic signatures of salmon populations showed no significant differences, however, A. simplex intensities between populations on the East and North coasts of Scotland suggest geographical differences in A. simplex transmission pathways. Finally, the expression of TNF-α1 is not significantly different between RVS severity, and nematode burden. Out of the four studied factors, increasing nematode intensities in Atlantic salmon populations, and the significant positive relationship of nematode intensities between the body (viscera and musculature) and the vent, are likely to explain the infestation of the vent by A. simplex. The underlying causes of RVS however remain uncertain and require further research. With incidences of RVS observed across a number of populations over a large spatial area, regional and global effectors such as warming sea surface temperatures, and the North Atlantic Oscillation are expected to play key roles in its aetiology.

By means of numerical modelling the cycling of iron between its various physical (dissolved, colloidal, particulate) and chemical (redox state and organic complexation) forms in the upper mixed layer of the ocean is analysed. Using the model an initial quantitative assessment is made of how this cycling influences iron uptake by phytoplankton and its loss via particulate export. The model is forced with observed dust deposition rates, mixed layer depths, and solar radiation at the site of the Bermuda Atlantic Timeseries Study (BATS). It contains an optimised ecosystem model which yields results close to the observational data from BATS. Firstly, the results of a zero-dimensional model approach show that the mixed layer cycle strongly influences the cycling of iron between its various forms. This was mainly attributed to the light dependency of photoreductive processes and to the seasonality of primary production. The daily photochemical cycle is driven primarily by the production of superoxide and its amplitude depends on the concentration and speciation of dissolved copper. Model results are largely insensitive to the dominant form of dissolved iron introduced via dust deposition, and also to the form of iron that is taken up directly during algal growth. In the model solutions, the role of the colloidal pumping mechanism depends strongly on assumptions made regarding rates of colloid aggregation and photoreduction rate. Secondly, a one-dimensional approach of the model is coupled with the General Ocean Turbulence Model (GOTM). The combined model was able to simulate the temporal patterns and vertical profiles of dissolved iron in the upper ocean at the BATS site reasonably well. Subsurface model profiles depended strongly on the parameter values chosen for loss processes affecting iron, colloidal aggregation and scavenging onto particles. Current estimates for these parameters result in depletion of dFe. A high stability constant of iron-binding organic ligands is required to reproduce the observed degree of organic complexation below the mixed layer. Solubility of atmospherically deposited iron higher than 2% leads to dissolved iron concentrations higher than observations. Despite neglecting ultraviolet radiation, the model produces diurnal variations and mean vertical profiles of dFe which are in good agreement with observations.

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-12T15:30:43Z No. of bitstreams: 2 Leite_FS-Tese2012-DOCEAN-tt.pdf: 7355705 bytes, checksum: cdd11be57564224083c3a2b8946fb3de (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)<br>Made available in DSpace on 2015-03-12T15:30:44Z (GMT). No. of bitstreams: 2 Leite_FS-Tese2012-DOCEAN-tt.pdf: 7355705 bytes, checksum: cdd11be57564224083c3a2b8946fb3de (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-09-26<br>FACEPE<br>A exploração de óleo e gás vem apresentando um rápido crescimento em regiões de baixa latitude, mesmo assim pouquíssimos experimentos e modelagens envolvendo vazamento de gás têm sido publicados pela comunidade científica. Este estudo foi desenvolvido de modo a aumentar o conhecimento a respeito do comportamento da pluma de gás durante um vazamento acidental em águas rasas. Os métodos usados e os resultados obtidos são apresentados neste estudo, assim como um modelo para simular o transporte e a dispersão de uma pluma de gás liberada em águas rasas. Primeiramente, experimentos de campo foram realizados através da simulação de um vazamento de gás natural a aproximadamente 30 m de profundidade na costa nordeste do Brasil. Quatro cenários distintos, com variadas condições de forçantes geofísicas, foram associados a diferentes fluxos de gás (de 3000 a 9000 L.h-1) e períodos sazonais (verão e inverno). Num segundo estágio, a análise de dispersão da pluma de gás foi realizada com os dados obtidos in situ. O modelo usou um volume de controle lagrangiano para discretização e simulou a evolução da pluma de gás associando a termodinâmica e o impacto desta na hidrodinâmica da pluma de gás. De acordo com os dados coletados, o transporte predominante da corrente ocorreu para sulsudoeste (nordeste) durante o verão (inverno). A diferença no diâmetro da pluma ocorreu principalmente na camada mais próxima à superfície. A pluma de gás deslocou-se para sul-sudoeste no verão e para nordestenorte durante o inverno. Os fluxos de gás liberados no assoalho oceânico pareceram não afetar a hidrodinâmica local. O movimento da pluma foi sempre influenciado pelas forçantes de maré e meteorológica, nesta ordem. Os resultados de modelagem indicaram que, à medida que a pluma sobe na coluna de água, a mesma é deslocada horizontalmente na direção da corrente predominante. A situação extrema estabeleceu um raio crítico (máximo deslocamento horizontal) da fonte de gás de 35,2 m. A comparação entre os dados medidos e os calculados mostrou que o modelo representou satisfatoriamente as principais características da liberação de gás, tais como o deslocamento, o diâmetro e o tempo de ascensão da pluma. Apesar das plumas apresentarem a largura média da mesma ordem de magnitude entre as medições e os cálculos, melhorias podem aumentar o desempenho do modelo durante o desenvolvimento inicial das plumas. Dados importantes e únicos foram coletados durante os vazamentos de gás, os quais contribuíram para a caracterização do comportamento de diferentes fluxos em diferentes períodos. Os experimentos forneceram uma base de dados para um modelo computacional que foi capaz de reproduzir o transporte e a dispersão de uma pluma de gás no ambiente marinho. O modelo foi capaz de prever o transporte e destino do gás liberado no ambiente. O mesmo pode, portanto, ser usado como uma ferramenta para planos de contingência de vazamentos acidentais de gás no oceano.<br>Underwater oil and gas exploration has been growing fast in low latitude regions, even though very few experimental data acquisition and modeling involving gas release in tropical and shallow waters have been published by the scientific community. This study was developed to increase the knowledge concerning the gas behavior during a subsurface blowout in shallow waters. The methods used and the results obtained from this study are presented, as well as a model to simulate the transport and dispersion of a subsurface gas plume released from shallow waters. At first, field experiments were carried out by simulating a subsurface blowout with natural gas at approximately 30 m depth in the Northeast Brazilian coast. Four distinct scenarios with varied conditions of geophysical forcing were associated with different fluxes (from 3000 to 9000 L.h-1) and seasonal periods (summer and winter). As a second stage, the analysis of the gas plume dispersion was accomplished with the data obtained from the above campaigns. The model used a Lagrangian control volume for discretization and simulated the gas plume evolution, associating thermodynamics and the impact of the thermodynamics on the hydrodynamics of the gas plume. The predominant transport occurred toward the south-southwest (northeast) during the summer (winter) period. The difference in the plume width occurred mainly in the upper surface layer. The gas plume displaced toward the south-southwest (northeast-north) during the summer (winter) period. The gas flow releases seemed not to affect the local hydrodynamics. The plume movement was always influenced by the tidal and meteorological forcings, in that order. The simulation results indicated that, as the gas plume rose in the water column, the same plume was horizontally displaced toward current predominant direction. The extreme situation provided a critical radius (maximum horizontal displacement) from the gas release source of 35.2 m. The comparison between the measured and the calculated data showed that the model satisfactorily represented the main features of the gas release, such as the displacement, diameter and ascending time of the plume. Although the mean plume widths have the same order of magnitude between the measurements and the calculations, improvements may enhance the model’s performance during the earlier plume development. Important and unique data were collected during these subsurface releases, which contributed to the characterization of the behavior of different blowouts in different seasons. The experiments provided a baseline for a computational model capable of reproducing gas plume transport and dispersion in the marine environment. The model was able to predict the gas release transport and fate in the environment. Thus it can be used as a tool for contingency planning of an accidental underwater gas release.

Part one of this thesis examined the tropical oceanic cetacean community occurring between Togo and Angola (6°N-11°S latitude).  Twenty-two cetacean species were recorded during 5905.3 hr of dedicated survey effort from platforms of opportunity between 2004 and 2009.  Sperm whales (<i>Physeter macrocephalus</i>) and humpback whales (<i>Megaptera novaeangliae</i>) were the most frequently-sighted species, and exhibited significant differences in occurrence related to water depth and survey month.  Five species inhabited both neritic and oceanic waters, while the remainder were exclusively oceanic.  The habitat preferences and niches (based on depth, seabed slope, sea surface temperature (SST) and frontal strength) of eight species were examined using classification trees and a principle component analysis.  Water depth and SST appeared to be the primary variables (of those examined) explaining the presence of most species.  Part two of the thesis was a study of the Atlantic humpback dolphin (<i>Sousa teuszii</i>), a species endemic to nearshore eastern tropical Atlantic (ETA) waters.  A total of 1,626.8 km of boat- and vehicle-based effort in Namibe Province during 2008, produced 52 <i>S. teuszii </i>sightings.  Further sightings were recorded during 53.7 hr of shore-effort at Flamingos (<i>n</i>=6) and opportunistically (<i>n</i>=13). Ten individuals were photo-identified. Multiple resightings (and an absence of unmarked animals) indicated low abundance, high site fidelity and year-round occurrence.  <i>Sousa teuszii </i>produced simple (85% had a single inflection point) whistles in the 2.5-23.4 kHz fundamental frequency range and broadband click trains with repetition rates varying from 5.8-250.8 clicks/s.  The implications of the findings for the future monitoring and conservation of cetaceans in the ETA are discussed.

L’analyse combinée d’observations et de sorties du modèle opérationnel Mercator Océan (appelé PSY4) a apporté un nouvel éclairage sur les récentes conditions océaniques du Bassin Eurasien Arctique occidental. Les mesures physiques collectées par deux plateformes autonomes dans le Bassin Eurasien occidental (0-350 m) ont indiqué que la couche de surface observée en 2017 était moins salée, et la couche chaude des eaux Atlantiques était moins profonde qu’en 2007-2012 (climatologie WOA13). PSY4 a apporté des informations complémentaires sur la nature des structures de méso-échelle documentées in-situ: dans le Bassin Nansen, une structure d’eaux Atlantiques issue du courant de bord a évolué en un tourbillon anticyclonique, tandis qu’une seconde structure à l’ouest du Plateau de Yermak concordait avec une branche d’eaux Atlantiques recirculant vers le Détroit de Fram. Les 14 années de sorties PSY4 ont montré qu’en hiver, les propriétés des eaux Atlantiques ont été considérablement modifiées par la convection hivernale profonde et par l’écoulement récurrent d’eaux moins chaudes et salées venant du plateau continental. Les régions du Plateau de Yermak et du talus continental sont devenues des « Zones Marginales de Convection » avec, à partir de 2011, l’absence occasionnelle de banquise en hiver ainsi que des couches de mélanges et flux océan-atmosphère fortement variables. Enfin, PSY4 a indiqué des changements de circulation dans le Bassin Nansen occidental, avec l’intensification de la Yermak Branch allant alimenter la Return Yermak Branch sur le flanc est du Plateau. PSY4 a également souligné la mise en place de nouveaux chemins empruntés par les eaux Atlantiques: dans le Sofia Deep, une circulation anticyclonique s’est développée. En aval du Plateau de Yermak, un courant s’est mis en place le long de l’isobathe 3800 m. A l’est de 20°E, ce courant a été alimenté par l’injection régulière de structures de méso-échelles issues du courant de bord<br>Combination of observations and Mercator Ocean operational model (PSY4 hereafter) outputs provided insights on the recent oceanic conditions in the changing Western Eurasian and Nansen basins, entry region for the warm and salty Atlantic Water (AW) to the Arctic Ocean. Autonomous platforms showed that the Western Eurasian Basin exhibited a fresher surface layer and shallower warm AW layer in 2017 than in the 2005‐2012 World Ocean Atlas climatology. PSY4 brought insights on the mesoscale structures observed in the halocline and warm layer. In particular, in the Nansen Basin a large mesoscale structure of AW from the boundary current turned into an anticyclonic eddy after the platforms passage. A second AW structure northwest of the Yermak Plateau, was a branch of AW recirculating back toward Fram Strait. The performance of PSY4 was assessed using independent observations over 2007-2020 in the Western Nansen Basin (WNB). We took advantage of 14 years of fields from PSY4 to examine winter conditions in the WNB over 2007-2020. PSY4 showed that deep winter convection and recurrent outflows from troughs northeast of Svalbard dramatically modified the AW. The northern Yermak Plateau-Sofia Deep and continental slope areas became “Marginal Convection Zones" in 2011 with, from then on, occurrences of ice-free conditions and mixed layer depths deeper than 200m in winter, and highly variable ocean-to-atmosphere heat fluxes. PSY4 also showed changes in circulation in the WNB over 2008-2020, with the strengthening of the Yermak Branch, which fed the southward Return Yermak Branch along the eastern flank of the Plateau. PSY4 highlighted the onset of new AW pathways: a recurrent anticyclonic circulation established in Sofia Deep. An offshore AW circulation developed downstream of the Yermak Plateau (following the 3800m isobaths). East of 20°E, additional AW from boundary current was injected in this offshore circulation, via enhanced basin-ward mesoscale activity

La variabilité de l’intensité du flux d’eaux atlantiques et de la nature des masses d’eau de surface le long des marges occidentales de la Norvège, de la mer de Barents et du Svalbard a été reconstituée sur la base des assemblages de coccolithes et dinokystes présents dans cinq carottes sédimentaires marines représentatives de l’Holocène terminal. Les résultats sont présentés sous la forme de reconstructions qualitatives et quantitatives (fonctions de transfert MAT) à haute résolution temporelle (échelle décennale à sub-séculaire). Un travail visantà valider les traceurs micropaléontologiques utilisés a été réalisé en parallèle à l’objectif principal, et s’est en particulier nourri de la collecte et de l’examen de populations vivantes distribuées le long de plusieurs transectszonaux en mer de Norvège, mer d’Islande et à travers le détroit de Fram.Nos résultats indiquent que la partie orientale des mers Nordiques (66 à 77°N) a été sujette à une tendance globale à l’augmentation du flux d’eaux atlantiques (AW) au cours des derniers 3000 ans. La dynamique récente de ce flux méridien est supposée répondre à la modulation long-terme de la force et de la localisation de la ceinture des vents d’ouest qui est essentiellement pilotée par l’Oscillation Nord Atlantique. Ce même mécanisme atmosphérique réconcilie le déplacement zonal et contradictoire du front arctique entre le domaine ouest-norvégien, et les façades occidentales de la mer de Barents et du détroit de Fram. La variabilité rapide du flux d’AW reproduit la succession des phases climatiques historiques classiques chaudes (Période Chaude Romaine, Période Chaude Médiévale, Période Moderne : flux accentué d’AW) et froides (Période Sombre, Petit Age Glaciaire : flux réduit d’AW) des derniers 2500 ans. Un événènement rapide de renforcement du flux d’AW en mers Nordiques a été identifié pendant le Petit Age Glaciaire entre 330 et 410 ans BP (cal.). Nos résultats indiquent que les variations d’intensité du flux d’AW vers l’Océan Arctique ont eu un impact majeur sur la distribution de la glace de mer arctique au cours du dernier millier d’années, les variations reconstruites de l’extension du couvert de glace à l’echelle de l’océan arctique étant parfaitement corrélées (échelle subséculaire) avec nos reconstructions qualitatives de la dynamique de l’AW au large du Svalbard et de la mer de Barents. La diminution importante de l’extension de la banquise durant le 20ème siècle est synchrone d’un flux record d’AW à travers le détroit de Fram, flux qui, d’après nos données, est sans précédent pour les derniers 3000 ans<br>Five marine sediment cores distributed along the Norwegian, western Barents Sea, and Svalbard continental margins have been investigated in order to reconstruct late Holocene changes in the poleward flow of the Norwegian Atlantic Current (NwAC) and West Spitsbergen Current (WSC) and the nature of the upper surface water masses within the eastern Nordic Seas. This research project is based on the use of dinocyst and coccolith assemblages for qualitative and quantitative reconstructions of surface water conditions from high resolution sediment cores, and involve upstream investigations on proxy reliabilities. The investigated area (66 to 77°N) was affected by an overall increase in the strength of the AW flow from 3000 cal. yrs BP to the Present. The long-term modulation of westerlies strength and location which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of the AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic Front between the area off western Norway and the western Barents Sea-eastern Fram Strait region. Submillenial changes in AW flow are organised according to known pre-Anthropocene warm (RWP, MCA and the Modern period: strong poleward flow) and cold (LIA, DA: weak poleward flow) climatic spells. A sudden short pulse of resumed high WSC flow interrupted the LIA in the eastern Nordic Seas from 330 to 410 cal. yrs BP. Our results are indicative of a major impact of AW flow dynamics on the Arctic sea ice distribution during the last millenium, when changes in reconstructed sea-ice extent are negatively correlated with the strength of the WSC flow off western Barents Sea and western Svalbard. The extensive decrease in sea ice extent during the last century is synchronous with an exceptional increase in AW flow. The previously reconstructed high amplitude warming of surface waters in eastern Fram Strait at the turn of the 19th century was therefore primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 years

Tese de Doutoramento apresentada á Universidade dos Açores, Horta<br>In this thesis the evolutionary relationships of the inshore fish fauna of the northeastern Atlantic and Mediterranean were assessed. Twelve coastal fish species from six families: Blenniidae, Labridae, Pomacentridae, Scaridae, Sparidae and Tripterygiidae, were studied using mitochondrial and nuclear molecular markers. Results were analyzed applying phylogeographic and histórical demography approaches. Species revealed four distinct phylogeographic patterns that were supported by genetic diversity and demographic parameters of the different populations: i) two distinct groups of populations (sometimes considered different species), one including the Mediterranean and the Atlantic coast of western Europe, and another including the Atlantic archipelagos of Canaries, Madeira and Azores (Chromis chromis/ C. limbata, Parabiennius sanguinolentus/ P. parvicornis and the two lineages of Trípterygion delaisi); ii) no appreciable genetic differentiation between any of the populations (Sparisoma cretense, Thalassoma pavo and Diptodus sargus); iií) marked differentiation of the Azorean population (Lipophrys phoíis and Coryphoblennius galeríta) and a clear divergence between Mediterranean and western European íocations as well as Madeira and Canaries (Coryphoblennius galeríta); and iv) one form in the Mediterranean and in the northeastern Atlantic coast (Parabiennius gattorugine) and another one in the Atlantic islands and European coasts (R ruber), thus in sympatry with P. gattorugine. These distinct phylogeographic patterns can be explained by a cornbination of differential effects of the Pleistocene glaciations in several areas of the Atlantic and Mediterranean and the particular thermal tolerances and dispersal capabilities of the species. The species conforming to the first pattern are warm water species that would not have been able to survive the colder glacial periods in the more affected areas such as western Europe,. eastern Canaries, the Azores and most of the Mediterranean. These species might have survived the cold periods in warmer refuges such as Madeira, the western Tropical coast of África and some southern pockets of the Mediterranean. After warmer conditions were restored, fishes surviving the glaciations in the western Tropical coast of África would have expanded northwards colonizing the northern coast of África and the Macaronesian islands, while fishes from the south of Mediterranean invaded the entire Sea and the adjacent European Atlantic coast. Isolation between the two refuges might have promoted divergence and eventually speciation. Colonization of the Azores woulid have been possible by fishes that survived in Madeira, and also in the western coast of África, with the intermediate islands of Canaries and Madeira acting as stepping stones. Species that conform to the pattern of no genetic differentiation among the populations are species with higher dispersal ability, which might have promoted a very fast mixing of the populations after warmer conditions were restored, erasing the signs of population differentiation. The third pattern was depicted for the two cold-water species studied. These species might have persisted during the Pleistocene cooling episodes in the less affected areas, among which are the Azores. The long term persistence of these species coupled with their limited dispersal ability Vera S. Domingues would have promoted the genetic differentiation of the more isolated locations such as the Azores and the Mediterranean. The fourth pattern pointed to a speciation in the Azores or Madeira followed by an invasion of the European shores. Concerning the Atiantic-Mediterranean transition, only one species, the blennild Coryphoblennius galerita, showed a clear and strong genetic differentiation between the two basins, that was accompanied by morphological differentiation. Historical isolation caused by sea level lowering at the Gibraltar Strait during the Pleistocene glaciations might have promoted the divergence between the two basins. The complex pattern of gyres and eddies of the Alboran sea can also constitute an effective physical barrier between the two regions. Other factors such as rirval behavior and the superficial currents during C. gaíeríta's spawning season my also have influenced the segregation of the two divergent lineages. Within the Mediterranean Thaíassoma pavo and Chromis chromis showed a restriction to gene flow south of the Greek Peloponnese, where a permanent anticyclonic gyre has been identified. This study contributes to further our knowledge on the evolutionary relationships of the coastal fauna of the Atlantic-Mediterranean, pointing out that features like thermal tolerances and dispersal ability of the species are amongst the important forces shaping the phylogeographic patterns of the species. ------ RESUMO ------ Nesta tese são analisadas as relações evolutivas da fauna piscícola costeira do Atlântico nordeste e do Mediterrâneo. Foram estudadas doze espécies de peixes costeiros pertencentes a seis famílias: Bienníidae, Labridae, Pomacentridae, Scaridae, Sparidae e Tripterygiidae, utilizando marcadores moleculares mitocondriais e nucleares. Os resultados foram analisados através de métodos filogeográficos e de demografia histórica. As espécies revelaram quatro padrões filogeográficos distintos, suportados peias diversidades genéticas e demografias históricas das diferentes populações: i) dois grupos distintos de populações (por vezes considerados espécies diferentes), um incluindo o Mediterrâneo e a costa oeste europeia, e outro incluindo os arquipélagos atlânticos das Canárias, Madeira e Açores {Chromis chromis/ C. limbata, Parablennlus sanguinolentus/ P. parvicornis e as duas linhagens de Trípterygion delaisi); ii) ausência de diferenciação genética entre as populações (Sparísoma cretense, Thalassoma pavo e Diplodus sargus); iií) acentuada diferenciação da população dos Açores (Lipophrys pholis e Coryphoblennius galeríta) e uma divergência clara entre o Mediterrâneo e o oeste europeu, bem como a Madeira e Canárias {Coryphoblennius galeríta); e iv) uma forma no Mediterrâneo e costa atlântica nordeste (Parablennius gattorugine) e outra nas ilhas atlânticas e na costa europeia [P. ruber), em simpatria com P. gattorugine. Estes padrões filogeográficos distintos podem ser explicados pela combinação dos efeitos diferenciados das glaciações do Pleístocénio em várias áreas do Atlântico e do Mediterrâneo com as tolerâncias térmicas e capacidades de dispersão das diferentes espécies. As espécies que se enquadram no primeiro padrão são espécies de água quente que durante os períodos glaciares mais frios não poderiam ter sobrevivido nas áreas mais afectadas como o oeste europeu, as ilhas este das Canárias, os Açores e a maior parte do Mediterrâneo. Estas espécies devem ter sobrevivido os períodos frios em refúgios mais quentes como a Madeira, a costa Tropical oeste de África e algumas bolsas de água mais quente a sul do Mediterrâneo. Após as condições mais quentes terem sido repostas, os peixes que sobreviveram às glaciações na costa Tropical oeste de África, ter-se-ão expandindo para norte, colonizando a costa norte de África e as ilhas da Macaronésia, enquanto que os peixes do sul do Mediterrâneo terão invadido todo este mar e a costa atlântica europeia adjacente, O isolamento dos dois refúgios deverá ter promovido divergência e eventualmente especiação. A colonização dos Açores deverá ter sido possível por peixes que sobreviveram na Madeira e também na costa oeste Africana, com as ilhas intermédias das Canárias e Madeira a actuar como stepping stones. As espécies que se enquadram no padrão de inexistente diferenciação populacional são espécies com maior capacidade de dispersão, o que terá permitido uma mistura rápida das populações após as condições mais quentes terem sido repostas, eliminando quaisquer sinais de diferenciação populacional. O terceiro padrão foi identificado para os duas espécies de água fria estudados. Estas espécies deverão ter persistido nas áreas menos afectadas, incluindo os Açores, durante os períodos frios do Pleistocénio. A persistência prolongada deste peixes, bem como a sua reduzida capacidade Vera S. Dorningues de dispersão terão promovido a diferenciação genética das regiões mais isoladas como os Açores e o Mediterrâneo. O quarto padrão aponta para um fenómeno de especiação nos Açores ou na Madeira, e posterior invasão das costas europeias. No que respeita à transição entre o Atlântico e o Mediterrâneo, apenas uma espécie, o biénio Coryphoblennius gaieríta, mostrou uma clara e forte diferenciação genética entre as duas bacias, acompanhada por diferenciação morfológica. O isolamento histórico causado pela redução do nível do mar no Estreito de Gibraltar durante as glaciações do Pleistocénio, poderá ter promovido a divergência entre as duas bacias. O padrão complexo de redemoinhos do Mar Alboriano pode também constituir uma barreira física efectiva entre as duas regiões. Outros factores como o comportamento larvar e as correntes superficiais durante a época de reprodução de C. gaieríta, podem ter também influenciado a segregação das duas linhagens divergentes. Dentro do Mediterrâneo, Thalassoma pavo e Chromis chromis revelaram a existência de restrição ao fluxo genético a sul da Peloponésia grega, onde um gyre anticiclónico foi identificado, Este estudo contribui para alargar o nosso conhecimento acerca das relações evolutivas da fauna costeira do Atlântico-Mediterrâneo, e aponta características como a tolerância térmica e capacidade de dispersão das espécies, como forças importantes para o delinear de padrões filogeográficos das espécies.

Several numerical experiments are carried out using the Bryan-Cox Ocean General Circulation Model to investigate the variability of the North Atlantic thermohaline circulation under steady, non-zonal, surface forcing and realistic geometry. To this end the annual mean surface forcing fields were derived from the climatological data sets of Levitus (1982), Hellerman and Rosenstein (1983) and, Schmitt et al. (1989). Further, Arctic freshwater flux, an important part of the hydrological cycle within the North Atlantic Deep Water formation region, is taken into account.<br>It is found that under present-day climatological surface forcing the system may oscillate at interdecadal period. The mechanism driving the oscillations is linked to changes in both the horizontal and vertical extent of convection in the northern "Labrador Sea". The structure of the surface freshwater flux forcing plays a major role in both the initiation and sustenance of the interdecadal oscillations. Allowing for a freshwater flux into the northern region of the "Labrador Sea" inhibits the interdecadal variability. The oscillations, however, appear, relatively insensitive to Arctic fresh water transport into the "Greenland Sea".<br>A detailed three-dimensional discussion of the physics behind the interdecadal oscillations is presented.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1988.<br>Vita.<br>Includes bibliographical references (p. 243-259).<br>by Michael Anthony Kaminski.<br>Ph.D.

The South Atlantic has a relevant role on the AMOC variability as it includes two main conduits of its upper-ocean return flow: the NBUC and the IWBC that carry, mainly, the SACW and the AAIW and are originated from the bifurcation of the SEC. One of the hypotheses of this work is that analyzing the bifurcation variability it is possible to get an index of the AMOC changes. Another hypothesis is that in a global warming scenario, changes in the hydrological cycle would drive modifications in the water masses that are part of the AMOC, and thus, contribute to its variability. Four global model results were used, with different forcing and spatial resolution. Results show that changes in the bifurcation are linked to modications in the currents both caused by variations in the wind stress curl. Good correlations were found between the SEC bifurcation at the surface and the AMOC. The NBUC seems to be the link between them. Shallowing of the SACW core is related to an increase of the salinity on neutral surfaces. The AAIW is occupying less space in the water column due to an increasing of the salinity in the neutral surfaces at 11°S, while the opposite happens at 27°S<br>The South Atlantic has a relevant role on the AMOC variability as it includes two main conduits of its upper-ocean return flow: the NBUC and the IWBC that carry, mainly, the SACW and the AAIW and are originated from the bifurcation of the SEC. One of the hypotheses of this work is that analyzing the bifurcation variability it is possible to get an index of the AMOC changes. Another hypothesis is that in a global warming scenario, changes in the hydrological cycle would drive modifications in the water masses that are part of the AMOC, and thus, contribute to its variability. Four global model results were used, with different forcing and spatial resolution. Results show that changes in the bifurcation are linked to modications in the currents both caused by variations in the wind stress curl. Good correlations were found between the SEC bifurcation at the surface and the AMOC. The NBUC seems to be the link between them. Shallowing of the SACW core is related to an increase of the salinity on neutral surfaces. The AAIW is occupying less space in the water column due to an increasing of the salinity in the neutral surfaces at 11°S, while the opposite happens at 27°S

Today, only 7 % of the Atlantic Rainforest, that once covered Brazil, remains scattered across the southern parts of the country. As the forest is rapidly disappearing, the government of Brazil has emerging interest of preservation. Thus more and more areas are turned into national parks and reserves. At the outskirts of one of these reserves, the Iracambi research station is situated. The center makes an effort to carry out applied research to find methods of preserving and learning about the forest. It is within that context the project described in this report has been performed. The project aimed to establish a water balance over Graminha Basin, the main river in the Iracambi research area. By doing this the understanding of the fluctuations of the amount of water in the ecosystem could increase. An important part of the objective was also to assess which methods can be used practically at Iracambi.The project was carried out during the rainy season from February 13th to April 12, 2012. During this time the water flow was measured at five stations along the river, using a current meter and instant slug-injection. Between six and fifteen flow measurements were made at each station. Slug- injection was generally the most suitable gauging method to use in the area. Precipitation was measured at two points. Evaporation was measured using an evaporation pan, and also calculated using the Penman-Monteith equation. Even though, the parameterization of the Penman-Monteith needs to be improved it was deemed to be the more suitable method for the area.The results give a rough estimate of the water balance during the period. It was concluded that the storage decreased during the project period. Based on the flow measurements and observations it was concluded that the areas covered by forest were less affected by the floods that occurred during heavy rainfalls than the areas covered by grass. Further on, the result of this report indicates that the Iracambi research station can continue to carry out assessments for changes in water flow, rainfall and evaporation with the simple equipment used in this project. However, more expensive and advanced equipment would be beneficial to establish a more accurate water balance.<br>Idag återstår endast 7% av den atlantiska regnskogen som en gång täckte Brasilien södra kust. Regnskogen försvinner snabbt vilket har lett till att Brasiliens regering de senaste åren visat ett ökat intresse att bevara regnskogen. Fler och fler områden har förvandlats till nationalparker och reservat. I utkanten till ett av dessa reservat ligger forskningsstationen Iracambi. Iracambi bedriver forskning i och runt området för att hitta metoder för att bevara regnskogen och öka kunskapen om området. Detta projekt är ett litet bidrag till detta arbete. Det övergripande syftet med projektet var att upprätta en vattenbalans över floden Graminhas avrinningsområde. Detta är huvudfloden i området och genom upprätta en vattenbalans kan förståelsen för förändringarna av vattentillgången i ekosystemet öka. Ett viktigt mål med projektet var också att finna verktyg som forskningsstationen Iracambi kan använda för kontinuerliga mätningar av de parametrar som ingår i vattenbalansen.Projektets genomfördes under regnperioden mellan den 13 februari och den 12 april, 2012. Flödesmätningarna utfördes vid fem mätstationer längs floden Graminha. Två typer av utrustning användes: flygel och konduktivitetsmätare. Rekommendationen för Iracambi var att fortsätta mätningarna med framförallt konduktivitetsmätaren. Uppskattningarna av avdunstningen genomfördes på två sätt: dels genom upprättandet av en evaporationspanna, dels genom beräkningar. Beräkningarna genomfördes med Penman-Monteith ekvationen och det kunde konstateras att även om de ingående parametrarna innehåller en del osäkerheter, så var detta den mest passande metoden för att beräkna avdunstningen. Nederbörd mättes på två platser med hjälp av enkla regnmätare konstruerade av pet-flaskor.Slutligen upprättades en vattenbalans för området. Utifrån denna kunde det konstateras att vattenmagasinet för hela orådet minskade under mätperioden. Utifrån flödesmätningar samt observationer kunde slutsatsen dras att skogsområdena drabbades mindre än de gräsbevuxna områdena av de kraftiga översvämningarna som uppstod under intensiva regn. Vidare visar resultaten att forskningsstationen Iracambi kan få en bra uppskattning av flödesförändringar, nederbörd och avdunstning med hjälp av den enkla utrustning som användes i detta projekt.<br>Minor Field Study

Ocean circulation is a fundamental component of the Earth's climate system. The Atlantic thermohaline circulation, driven by deep convection at high latitudes, has a central role in regulating European climate through its transport and redistribution of heat. Either directly or indirectly, Mediterranean Water (MW) provides the high salinities found in the Nordic Seas which are required to precondition for deep convection. The precise mechanisms and pathways remain undetermined and yet are fundamental to understanding the effect that any change in the Mediterranean Outflow may have on circulation and ultimately on climate. This thesis investigates the transport of MW in the North Atlantic Ocean using hydrographic and model data. The primary objective is to quantify how much MW flows northwards and how much flows westwards from its source in the Gulf of Cadiz. Two boxes (Med Boxes) were constructed using hydrographic sections in the eastern North Atlantic enclosing the Strait of Gibraltar and Mediterranean Outflow. Inverse methods were used to determine the velocity field from which volume transports and salt fluxes were calculated. The main northward flow of MW across 41°N occurs east of 12°W, at depths of 500 to 1500 m, and transports 50 to 75% of the MW. An advective westward pathway across 20°W transports MW at similar depths into the ocean interior between 35°N and 40°N. Insignificant salt fluxes across the southern section (24°N) at MW depths confirm that no MW crosses the southern Med Box boundary. The net overturning circulation of the Med Box, with inflowing surface waters and outflowing intermediate waters, is attributed both to the exchange at the Strait of Gibraltar and also to water mass transformation associated with entrainment of North Atlantic Water into the Mediterranean Outflow. The magnitude of the circulation provides an estimate of this entrainment of 1.6 ± 0.6 Sv, within the Med Box boundaries. For comparison with these observational estimates, the model used is OCCAM, a level model from the Ocean Circulation and Climate Advance Modelling Project. The primary reason for choosing this model is that experiments have been undertaken with the Strait of Gibraltar both open and closed, enabling a new approach to the investigation of MW transport. MW is identified using the salinity difference between the two model experiments. Although the model circulation (in the open-Strait run) has a similar net overturning to the hydrography, different MW transport pathways are observed. A weak and variable northward pathway along the Iberian Peninsula and a strong southwestward flow from the Gulf of Cadiz result in a higher proportion of MW flowing westwards (61%) than northwards (39%). Seasonal variability is observed, with maximum westward flow in Autumn (70%) and minimum in Spring (50%). There is no evidence in the model that the northward boundary current provides a direct route for Mediterranean salt to reach the Nordic Seas.

The last two glacial terminations represent the most recent, and best documented, periods of Earth warming in the geological record. During these terminations atmospheric CO\textsubscript{2 }rose by approximately 100 ppm and global mean temperatures increased by 4-6\textsuperscript{o}C. Whilst the driver for these deglaciations ultimately derives from changes in the insolation forcing at the edge of the atmosphere, feedbacks within the Earth\textquoteright s climate system act to amplify these small external forcings tipping the Earth from a cold glacial climate state to a warm interglacial climate state. A key question in Quaternary climate science is understanding which feedbacks are important in regulating global climate on glacial-interglacial timescales. On this topic, the Southern Ocean has long been considered to be an important player in regulating atmospheric CO\textsubscript{2 } on glacial-interglacial timescales. This thesis investigates some of the hypothesised drivers of changes in atmospheric CO\textsubscript{2 } on glacial-interglacial timescales by generating high-resolution multi-proxy records from the Southern Ocean spanning the last two glacial terminations. In particular, I focus on changes in the structure, circulation and biological productivity within the sub-Antarctic zone. A change in the deep ocean density structure has been hypothesised to have resulted in the release of CO\textsubscript{2 } from the deep ocean. Centennial records from the sub-Antarctic are used to reconstruct deep and intermediate water density for the first time. I demonstrate that timing of the major breakdown in the density gradient of the ocean significantly lagged the breakdown in the chemical gradient, suggesting that changes in the deep ocean density structure were not the major driver of the deglacial rise in atmospheric CO\textsubscript{2 }. Changes in the density structure of the Southern Ocean likely had significant implications for global circulation. In particular, the flow of low salinity water through the Drake Passage is thought to be important in setting the strength and geometry of Atlantic Overturning Circulation. Drake Passage through-flow speed was reconstructed from two sites in the central and northern margins of the Antarctic Circumpolar Current downstream of Drake Passage. These records suggest a very different structure of Antarctic Circumpolar flow through Drake Passage during glacial periods, and evidence significant changes in ocean temperature as a result of pronounced reductions in Drake Passage through-flow. The strength of the biological pump has long been identified as an important player in regulating atmospheric CO\textsubscript{2 }. In particular, a strong glacial increase in sub-Antarctic productivity has been observed at open ocean sites in the South Atlantic and Indian Ocean. However, the glacial-interglacial changes in productivity in sub-Antarctic shelf settings are less well-documented. The new high-resolution records presented here from the sub-Antarctic southwest Atlantic suggest a significant change in the CaCO\textsubscript{3}:C\textsubscript{org} ratio which likely has implications for the surface ocean\textquoteright s ability to uptake CO\textsubscript{2 }.

Subtropical mode water is a voluminous body of water in the ocean whose main feature is the homogeneity in both vertical structure and horizontal extension. The subtropical mode water (STMW) of the southwest Atlantic is formed between the months of July and October near the Brazil-Malvinas confluence and along the Brazil Current recirculation gyre. The formation region extends on the order of 3000 km zonally, from 20°W to 50°W, and 1000 km meridionally, from 30°S to 40°S, and it is typically about 170 m thick. In situ data from pressure-equipped inverted echo sounders (PIES) installed in the western portion of the basin, along 34.5°S, are available from 2009 to the present. These data after processed and calibrated can provide an unprecedented description of the STMW involving processes since its formation at the surface until the final stage of its residence in the interior of the ocean. Temperature and salinity data estimated by the PIES are based on empirical look-up tables that relate the acoustic travel time with the baroclinic structure of the ocean. This technique is known as the Gravest Empirical Mode (GEM), and here it is used to detect profiles containing homogeneous segments of temperature and salinity that characterize the mode water. The GEM method was seasonally corrected to reconstruct surface variability necessary for STMW formation. The interannual covariance between STMW layer thickness and the Brazil Current was calculated, but no significant correlation at that time scale was observed. The mode water layer detected was about 220 m ± 55 m thick on all sites, agreeing with previous studies.<br>A água modal subtropical é um grande volume de água no oceano cuja característica principal é a homogeneidade nas estruturas vertical e horizontal. A água modal subtropical do sudoeste do Atlântico é formada entre os meses de julho e outubro perto da confluência Brasil-Malvinas e ao longo da recirculação da Corrente do Brasil. A região de formação se estende na ordem de 3000 km zonalmente, de 20°W a 50°W e 1000 km meridionalmente, de 30°S a 40°S, e tipicamente tem cerca de 170 m de espessura. Dados in situ de ecossondas invertidas com sensor de pressão (PIES) instaladas na porção ocidental da bacia, ao longo de 34,5°S, estão disponíveis a partir de 2009 até o presente. Estes dados após o processamento e calibração podem fornecer uma descrição sem precedentes da Água Modal Subtropical do Atlântico Sul envolvendo processos desde sua formação na superfície até o estágio final de sua permanência no interior do oceano. Os dados de temperatura e salinidade estimados pelos PIES são baseados em tabelas de referência (look-up tables) que relacionam o tempo de retorno do sinal acústico com a estrutura baroclínica do oceano. Esta técnica é conhecida como o Gravest Empirical Mode (GEM),e aqui é usado para detectar perfis contendo segmentos homogêneos de temperatura e salinidade que caracterizam a água modal. Foi aplicada uma correção sazonal ao método GEM para reconstruir a variabilidade da superfície necessária para a formação STMW. A covariância interanual entre a espessura da camada STMW e a corrente do Brasil foi calculada, mas não foi observada correlação significativa naquela escala de tempo. A camada de água em modo detectada foi de cerca de 220 m ± 55 m de espessura em todos os sites, concordando com estudos prévios.

Observations of interannual variability in 18 Water (Talley and Raymer 1982) and Gulf Stream transport (Worthington 1977) motivate an ocean model sensitivity study. The North Atlantic circulation is simulated with a three-dimensional isopycniccoordinate GCM. Idealized anomalous buoyancy-forcing fields (associated with outbreaks of cold, dry continental air over the Gulf Stream/Sargasso Sea region) are constructed. In a series of sensitivity experiments, wintertime buoyancy loss over the Gulf Stream and Sargasso Sea is thus increased to varying degrees, with anomalous ocean-to-atmosphere buoyancy fluxes of up to double climatological values. Under excess buoyancy loss, winter mixed layer depths increase, and a greater volume of model 18 Water is formed. End-of-winter mixed layer density also increases, leading to the formation of a denser variety of 18 Water. The anomalous 18 Water recirculates around the Sargasso Sea as a signal of low potential vorticity, which spreads out and weakens on a decadal timescale. Strengthened horizontal pressure gradients in the vicinity of the anomalous 18 Water drive intensified baroclinic transports at the "immediate" end of winter (in March), after which a full-depth barotropic intensification of the Gulf Stream develops. Strongest intensification occurs in May, when the Gulf Stream barotropic transport is increased locally by up to 10 Sv. The anomalous transports which account for barotropic intensification are confined to deep and abyssal layers of the model. Where the associated anomalous bottom currents traverse isobaths, "extra" bottom pressure torque (BPT) is invoked. An anomalous BPT term in the barotropic vorticity balance may therefore account for the intensification. Computed from the model fields of density and sea surface height, such a term does appear to produce the extra negative vorticity associated with anticyclogenic intensification. It is concluded that wintertime excess buoyancy loss drives a springtime barotropic response of the subtropical gyre, through BPT, due to "JEBAR" (the Joint Effect of Baroclinicity And Relief). The Gulf Stream intensification decreases after May as lateral eddy mixing weakens anomalous cross-stream pressure gradients. This eddy mixing is parameterized in the model by a layer thickness diffusion velocity, ud, nominally chosen to be 1.0 cm s'1. Further experiments establish the sensitivity of intensification strength to the choice of ud. With ud = 0.1 cm s"1 (weak thickness diffusion), the intensification is increased by ~50%, while, for ud - 10 cm s"1 (strong thickness diffusion), the intensification is roughly halved. These further sensitivity experiments also reveal the varying degrees to which the model subtropical gyre can be dominated by diffusive eddy mixing (Rhines and Young 1982a, 1982b) or adiabatic (nondiffusive) ventilation of the thermocline (Luyten, Pedlosky and Stommel 1983). Recent (1980-97) interannual variability in the formation and recirculation of 18 Water, and other water masses, is deduced from observed surface heat and freshwater fluxes. Interannual variations in the strength of 18 Water renewal (thus deduced) and a wintertime index of the North Atlantic Oscillation (NAO) are found to be strongly anticorrelated (with a correlation coefficient of -0.70, statistically significant at a 99% confidence level). A further sensitivity experiment establishes that anomalous wind forcing, characteristic of a minimum phase in the NAO, does not intensify the Gulf Stream in the manner of excess cooling. It is concluded that 18 Water is more strongly renewed, with accompanying Gulf Stream intensification, under NAO-minimum buoyancy forcing.

To better understand how the evolution of Cenozoic deep-water circulation related to changes in global climate and ocean basin configuration, we generated Nd isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track deep water mass composition through time. We used fossil fish debris from ODP Sites 1262-1264 (Leg 208), spanning present-day water depths of 2500-4750 m, to reconstruct the isotopic signature of deep waters over the past ~53 Ma. The data indicate an initial transition from relatively non-radiogenic values (??Nd=~-10) at 53 Ma to more radiogenic values (~-8.5) at ~32 Ma. From ~32 Ma to 3.85 Ma, the Nd signal becomes more nonradiogenic, ~-12.3 at the top of the record. Comparison of our data with Nd isotopic records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values (~-10.5) in the 53??32 Ma interval and a trend toward more non-radiogenic values beginning at ~20 Ma. The data likely reflect an overall shift from a Southern Ocean deep water source to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic values at the base of the record reflect a Southern Ocean source of deep water. The shift toward more radiogenic values indicates an increased contribution of Pacific waters to the Southern Ocean source as the tectonic gateways changed after ~35-33 Ma. The subsequent trend toward more non-radiogenic Nd isotope values is approximately concurrent with the increase of benthic foraminiferal ??18O values, based on comparison with a compilation of global data. Thus, changes in oceanic gateway configuration in addition to overall cooling and the build-up of continental ice on Antarctica may have altered the Nd isotope character of Southern Ocean deep waters during the early Oligocene.

A proxy for the North Atlantic gyre circulation has been developed, using sea-surface height from altimetry. In conjunction with the winter North Atlantic Oscillation (NAO) index, statistical analysis has been applied to understand the key mechanisms of surface water partial pressure of CO2 (pCO2) variability, both on the seasonal and inter-annual timescale. With respect to the seasonal amplitude of surface pCO2 in temperate regions (>40°N), it is found that the gyre circulation strength, in response to the winter NAO index, drives this seasonal amplitude. Under positive NAO index winters, the formation of mode waters is favoured through strong surface cooling. This deepens the mixed layer, entraining carbon and nutrient-rich subsurface waters into the surface layer and increasing the surface pCO2 in winter. This deep winter mixing, bringing up nutrients in combination with enhanced advection of nutrients from the subpolar region, may also enhance and prolong the following spring bloom, decreasing the pCO2 in both spring and early summer. Thus, the seasonal amplitude of surface pCO2 under a positive NAO phase would increase. Under negative NAO winters, surface cooling is not as pronounced compared to a positive NAO winter and therefore the mixed layer is not as deep. Thus, both vertical and horizontal (via advection) carbon and nutrient entrainment are reduced thereby decreasing the pCO2 in winter and potentially weakening the following spring bloom. Thus the seasonal amplitude of surface pCO2 under a negative NAO phase would decrease. The subtropical regions (25 - 40°N) are also subjected to similar processes as the temperate regions, under both positive and negative NAO winters. However, the above-mentioned lagged effect of carbon-rich sub-surface water and nutrient entrainment in winter on the intensity of the spring bloom has to be treated with caution given the lack of statistically significant correlations between the surface pCO2 in winter and the proxy for carbon-rich subsurface water in spring. On inter-annual timescales, the phase of the winter NAO alters the ocean circulation in all regions. Under a positive NAO index, the subtropical gyre is more spun-up and with increased SST, increasing the annual mean pCO2. In the temperate zone, the interplay between carbon entrainment and biological drawdown dominates, dampening the inter-annual pCO2 variability.

Les Eaux Atlantiques (AW) sont cruciales pour le budget de sel et de chaleur de l'Arctique. Ce doctorat apporte de nouvelles informations sur l'entrée des AW dans la région du nord Svalbard. Les plateformes IAOOS ont collecté pendant la campagne N-ICE2015 les premières données hydrographiques d'hiver de la région. Elles ont documentées des eaux chaudes peu profondes sur le talus continental du Svalbard qui ont généré des flux de chaleur océan-glace atteignant 400 W/m2 et faisant fondre la glace. Cette chaleur est amenée des AW vers la surface par des ondes quasi-inertielles causées par des tempêtes hivernales, de grandes marées barotropes sur des pentes raides et/ou des ajustements géostrophiques. Les extensions de glace sont très différentes entre 2015 et 2016. Les sorties du modèle opérationnel de Mercator Ocean (1/12°) suggèrent que les flux de chaleur orientés vers la surface et induits par la convection expliquent ces différences. En plus de la Svalbard Branch et de la Yermak Branch, le modèle présente un chemin robuste l'hiver à travers le plateau du Yermak: la Yermak Pass Branch. Enfin, le modèle suggère une activité méso-échelle importante le long du courant des AW. Les propriétés de la Yermak Pass sont examinées avec un an de données ADCP (2007-2008) dans la Yermak Pass. Le courant est dominé par la marée. En hiver, des tourbillons baroclines d'AW avec une périodicité de 5-10 jours et des entrées sporadiques d'AW tous les un/deux mois sont observés, transportant les AW vers l'Est. Le modèle suggère que la Yermak Pass Branch est une structure robuste d'hiver les 10 dernières années et transporte en moyenne 31% du transport volumique du West Spitsbergen Current<br>The Atlantic Water (AW) inflow is crucial for the heat and salt budget of the Arctic. This PhD thesis brings new insights to the inflow of AW in the area north of Svalbard. The IAOOS (Ice Atmosphere Ocean Observing System) platforms were deployed during the N-ICE2015 expedition which gathered the first winter hydrographic data in the area. They document shallow warm water over the Svalbard continental slope that melts sea ice with ice-ocean heat fluxes reaching up to 400W.m-2. Heat is brought from the AW layer up to the surface through near-inertial waves generated by winter storms, large barotropic tides over steep topography and/or geostrophic adjustments. Sea ice extent largely differs between winters 2015 and 2016. 1/12° operational model outputs from Mercator-Ocean suggest that convection-induced upward heat fluxes explain the differences. Model outputs are also used to examine the AW inflow pathways : besides the Svalbard Branch and the Yermak Branch, the model shows an AW winter pathway not much documented before : the Yermak Pass Branch across the Yermak Plateau. Finally, the model suggests an important mesoscale activity throughout the AW flow. The Yermak Pass Branch properties are examined using one-year (2007-2008) of moored ADCP data in the Yermak Pass. The flow is largely dominated by tides. In winter, baroclinic eddies of AW with a periodicity of 5 to 10 days and pulses of AW monthly/bimonthly are found, carrying AW eastward through the Pass. Model outputs suggest that the Yermak Pass Branch is a robust winter pattern over the last 10 years, carrying on average 31% of the volume transport of the West Spitsbergen Current