This dissertation investigates the energetics of the Indian Ocean Meridional Overturning Circulation (MOC) using hydrographic data (Part I), and the interaction between a broad band internal wave field and a mean flow using idealized numerical simulations (Part II). The main objective of this work is to quantify how much energy is needed to drive the Indian Ocean MOC and to compare this with the energy available in the internal wave field. The turbulent dissipation needed to sustain the MOC is estimated by assuming a `mixing efficiency' of 0.2 and an advective-diffusive balance in neutral density layers. The advective transport of mass into this box-model is based on published estimates of the flow field at 32�S and the Indonesian Through-flow. A comparison of the large scale dissipation rates with estimates of the input of energy by the tides and the wind shows that most published overturning solutions require more energy than is likely to be available. This result suggests that energy budgets may be useful as constraints in inverse models. Estimates of turbulent dissipation due to internal wave breaking are inferred from in-situ observations of shear and strain using a fine scale parameterization. The isoneutral mean of the inferred internal wave dissipation rates is about one order of magnitude smaller than dissipation rates inferred from the large scale flow fields. This result appears robust when considering potential sampling biases in the internal wave observations and leads to the main conclusion of this work: the Indian Ocean MOC cannot primarily be driven by internal wave breaking. A preliminary investigation into other processes capable of dissipating energy in the ocean interior shows that the MOC may be closed by hydraulic turbulence in the numerous Fracture Zones in the Indian Ocean.

The thickness and continuity of volcanic cover at slow-spreading ridges is variable. Magmatically ‘robust’ regions are interspersed with areas which experience little volcanism. Near the Fifteen-Twenty Fracture Zone (FTFZ), (MAR), volcanism appears exceptionally limited. Here, spreading at numerous sites is instead accommodated by extension on low-angle detachment faults, exposing peridotite to form oceanic core complexes (OCCs). Little is known about the mechanisms controlling the transition between spreading states. This study investigates these mechanisms in detail (MAR, 12º6’N-14°N). Basalts around the FTFZ are E-MORBs with a HIMU-FOZO flavour. There is no evidence that melt production is currently lower at OCC spreading sites than the surrounding magmatic areas. The geochemistry of dykes (OCC surface, 13º19’N,-44º95W) shows that melt here is diverted along the detachment fault, resulting in reduced volcanism in the axis. The mantle source in this region was extensively depleted during a previous melting episode(s). This study finds that the source was also variably veined with refertilising material of HIMU-FOZO character. Basalts erupted immediately prior to OCC formation, and now located off-axis, (13º19’N,-44º95W) are geochemically bimodal, and different to the on-axis melts. Trace element and geochemical modelling data shows that ‘M1’ (LREE & volatile-rich, CPX-bearing E-MORBs) are high-pressure, garnet-phase, low melt fractions, whilst ‘M2’ (less enriched, flatter REE profiles) are low melt fractions formed by spinel-phase melting. In areas of exceptional bulk source depletion, melt production is limited by the geochemistry of the source.’ M1’ basalts result from rapid melting and extraction of a small volume of enriched vein material. This locally cools and dehydrates the source. Low melt fractions ‘M2’ are then generated from this depleted source. Due to the lack of fusible components, melt production remains insufficient to sustain magmatic spreading, and an OCC forms. Thus, periods of low melt production, resulting directly from mantle compositional characteristics, drive the transition from magmatic to ‘fault-dominated’ spreading.

The Atlantic Meridional Overturning Circulation (MOC) plays an important role in maintaining western Europe’s moderate climate. Although expected to weaken under increasing greenhouse gas concentrations, the magnitude of the response remains uncertain. Monitoring of the Atlantic MOC strength at 25ºN commenced in 2004 as part of the UK Rapid Climate Change programme. Prior to this, detection of such a slowing of the MOC and its associated meridional heat transport was inhibited by the temporally sparse observations of its strength. This thesis aims to extend the time series of Atlantic MOC at 25ºN back to 1980 using historical observations, thus constraining the magnitude of its recent interannual variability. Analysis of transatlantic hydrographic sections at 25ºN show the annual average MOC to have varied in strength by approximately 25% over the last 50 years, with weaker overturning in 2004 than previously computed. Temporal resolution of the dataset is increased through decomposition of the Atlantic MOC at this latitude into its Ekman component computed from wind stress climatology, transport of the Florida Current from cable observations and mid-ocean geostrophic transport from CTD or moored temperature and pressure derived boundary dynamic height profiles. The resulting time series constrain interannual fluctuations of the Ekman, Florida Straits and mid-ocean baroclinic geostrophic transports at ± 1, ± 2, and ± 3 Sv respectively between 1980 and 2005. In addition to interannual fluctuations in strength, evidence is found for a 2 to 3 Sv weakening of the MOC between 1980 and 2005. The underlying changes of increased mid-ocean southward transport of thermocline waters and decreased southward flow of lower North Atlantic Deep Water are consistent in sign, although of reduced magnitude, with the transatlantic hydrographic sections observations. This thesis presents and discusses these findings along with the relative merits of different datasets for detecting such variability.

The phenomenology, generation and associated dynamics of short period seiche oscillations observed along the northern coast of the Maltese Islands are studied from a set of densely sampled, long term hydro-meteorobgical observations made at a permanent sea level gauge, together with simultaneous observations of bottom pressure recordings at offshore positions and across the Malta Channel. This coastal seiche, known locally as the 'milghiibd, manifests itself in conjunction with the occurrence of mesoscale atmospheric gravity waves travelling in the lower troposphere. The associated open sea waves excite the water bodies of the various inlets, bays and harbours into resonant osculations which reach a range ofup to lmin Melfeha Bay. Numerical experiments based on the free surface, non-linear Princeton Ocean Model (POM) in 2D mode explain the response characteristics of two adjacent wide-mouthed open embayments. The seiche-induced barotropic circulation and impact on the flushing ofMellieha Bay are studied by means of an advection-diffusion scheme implemented within POM. Sea level signals on the synoptic, planetary wave and seasonal scales dominate the residual spectrum A multiple regression model and a novel analytic technique based on the wavelet transform provide in combination a very effective means of studying the composition ofthe sea level signal and the dependence of its variability in time on one or more correlated parameters. Atmospheric pressure is the predominant factor determining the sea level variability at frequencies lower than 0.75cpd. In the upper synoptic frequency (0.3 < f < 0.5cpd) the response is very close to isostatic, with an average gain of 0.7. At other frequencies the overall response is non-isostatic implying that other factors besides mesoscale atmospheric pressure forcing contribute to the sea level variability. On account of the station's position close to the latitudinal axis of the Strait of Sicily, these signals are important in understanding the control ofthe Strait on intra-basin exchanges. Seasonal changes in the mean sea level show a major minimumin March and a major maximum towards the last months ofthe year. Besides the usual steric and direct meteorological effects, this variability is attributed to adjustments in the mass balance ofthe whole Mediterranean basin.

The meridional overturning circulation (MOC) at 26.5N in the Atlantic has a standard deviation of 4.9 Sv and contains large fluctuations at subannual periods. The geostrophic component of the MOC is believed to be influenced on subannual timescales by eddies and Rossby waves. To quantify this effect, the vertical structure and surface characteristics of westward propagating signals are studied using altimetry data and full-depth mooring measurements from the RAPID array at 26.5N. Westward propagating features are observed in the western North Atlantic in both datasets and have periods of 80-250 days in the first baroclinic mode. These features are still observed by the RAPID moorings 20 km offshore of the western boundary. The effect of eddies and Rossby waves on the geostrophic transport is quantified by representing their vertical structure with the first baroclinic mode. In total, 42% of the variance of the transbasin thermocline transport inferred from geostrophic calculations at 26.5N can be attributed to first mode variability, which is associated with eddies and Rossby waves at periods of 80-250 days. The standard deviation of the transbasin thermocline transport due to eddies and Rossby waves is estimated to be 2.6 Sv. Having observed eddies to propagate towards the western boundary; the aim of the second section is to study the eddy energy sink at the boundary as one component of the energy redistribution from large scale winds to smaller scale internal waves. This section investigates the generation of internal waves by eddies in the North Atlantic western boundary where eddies dissipate. The eddy presence and decay are measured from the altimetric surface relative vorticity associated with an array of full-depth current meters extending -100 km offshore at 26.5N. In addition, internal waves are analysed over a topographic rise from 2-year high-frequency measurements of an Acoustic Doppler Current Profiler (ADCP), which is located 13 km offshore in 600 m deep water. Despite a polarity independence of the eddy decay observed from altimetric data, the bottommost 100 m flow is enhanced for anticyclones (25.2 s-1) compared with cyclones (-4.7 cm s-1). Accordingly, the internal wave field is sensitive to this polarity-dependent deep velocity. This is apparent from the eddy-modulated enhanced shear spectra and dissipation rates, which are obtained from a finescale parameterisation, =2.8x10-9 W kg-1 for |v|>8 cm s-1, whilst =0.9x10-9 W kg-1 for |v|<8 cm s-1. The local dissipation of anticyclones significantly contributes to the eddy decay at the western boundaries. The present study underlines the importance of oceanic western boundaries for removing the energy of low-mode westward propagating eddies to higher mode internal waves.

The work presented in this Thesis concerns the large-scale circulation of the Indian Ocean and follows three lines of investigation: (i) decadal variability of the subtropical gyre circulation; (ii) decadal variability of the deep meridional overturning circulation (MOC); and (iii) the influence of diapycnal diffusivity on quasi-steady MOC states. The decadal variability of the subtropical gyre transport over the ocean interior (away from boundary currents) is investigated using hydrographic data from 32°S. Estimates of the relative gyre transports are: 41 ± 5.1 Sv (1 Sv = 106 m3s-1) for 1987, 42 ± 7.0 Sv for 1995 and 58 ± 7.0 Sv for 2002. This represents a 40% increase from 1987 to 2002. The main areas of change in the geostrophic transports are just east of Madagascar Ridge and around Broken Plateau, which is consistent with differences observed in the isopycnal depths in these areas. Maps of contoured velocity suggest that most of the change happened between 1995 and 2002, which supports the transport estimates. The 1987 and 2002 hydrographic data are then combined with a regional model of the Indian Ocean to investigate the impact that changes in conditions near 32°S might have on the deep MOC. The model has lateral open boundaries at 35°S for the Southern Ocean and 122°E for the Indonesian Throughflow. The meridional velocity field dominates over density at the southern boundary (SB) in determining the basin-wide deep circulation on decadal timescales. The initial adjustment of the deep MOC to the first 5-6 years of model integration and shows a large sensitivity to the SB conditions. With ‘best’ estimates of the flow field near 32°S the model shows a 6 Sv and 16 Sv deep MOC for 1987 and 2002, respectively. There are also changes in the zonal structure of the deep circulation. The results suggest that the Indian Ocean exhibits decadal variability in the size and structure of the deep MOC. Furthermore, the apparent inconsistency between previous non-GCM and regional GCM studies may be a result of the lateral boundary conditions, rather than a conflict in the model dynamics. 200-year model integrations suggest that quasi-steady MOC states in the Indian Ocean are reached on century time scales. The size, structure and adjustment time of the quasi-steady deep MOC are controlled by the distribution of diapycnal diffusivity (Kd). The zonal mean distribution of Kd required to support the prescribed deep inflow at the model SB can be estimated using a one-dimensional (1-D) advective-diffusive balance in isopycnal layers. The 18 Sv overturning circulation put forward by Ferron and Marotzke [2003] (FM) collapses when their model configuration is integrated to quasi-steady state under a number of different Kd regimes. With a diagnosed Kd field only 70% of the FM circulation can be supported in quasi-steady state, and the Kd values are an order of magnitude larger than recent observations suggest. The results imply that one can get a good a priori estimate of the Kd-field required to support a quasi-steady model MOC by applying a 1-D advective-diffusive balance in isopycnal layers to the SB conditions. Overall, the research highlights the need to implement improved estimates of (nonuniform) Kd in ocean GCMs when investigating quasi-equilibrium model states.

We present a prediction of the strength of the meridional overturning circulation (MOC) in the Atlantic Ocean during the 21st century, and a quantitative estimate of its uncertainty. The MOC has been suggested as a potential source of abrupt climate change, with the ability to alter the climate of the North Atlantic on a short time-scale. The prediction takes the form of a calibrated uncertainty analysis, combining observations of the MOC, an ensemble of runs from a climate model, and expert knowledge, in a Bayesian fashion. Uncertainty in model behaviour due to the model structure and forcing is explored by running an ensemble of the Earth system model of intermediate complexity GENIE-1. Input parameters representing physical constants, simplified processes, and forcings are varied across the ensemble in a designed computer experiment. We develop quantitative and qualitative methods to compare observational data of the MOC with corresponding output from the ensemble, to learn about plausible input configurations of the model. Dimension reduction is used to express patterns of variation in model behaviour across the ensemble in a low-dimensional form. The ensemble is used to train an emulator; a fast statistical approximation to the expensive model, that includes an estimate of uncertainty due to the limited size of the ensemble. By training the emulator using the low-dimensional representations of the output, we are able to predict high-dimensional model output at input configurations not tested in the original ensemble. This allows a more complete expression of the uncertainty in the evolution of the MOC throughout the 21st century.

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.

Neste estudo determinou-se o nonilfenol - um composto xenobiótico utilizados na fabricação de antioxidantes, aditivos para óleos lubrificantes e produção de surfactantes etoxilados - e o bisfenol A - um composto químico utilizado na produção de diversos produtos, como, plásticos policarbonatos, resinas epóxi e retardantes de chama. Ambos exibem atividade estrogênica em concentrações abaixo de 1ng L-1 - em cinco pontos de coleta na cidade de Americana, SP. Devido à ampla utilização, esses compostos estão presentes em esgoto industrial em quantidades substanciais. A primeira etapa deste estudo foi a validação dos método analítico seguindo o Método 8270D da United States Environmental Protection Agency (USEPA) que descreve o procedimento de validação para os compostos semivoláteis analisados por cromatografia gasosa acoplada a espectrometria de massas (GC/MS). Os limites de detecção e de quantificação do método para a determinação do nonilfenol foram, respectivamente, 1 e 5 &micro;g L-1. O coeficiente de determinação (R2) e a recuperação média para o nonilfenol foram, respectivamente, 0,99 e 99,04%. Os limites de detecção e de quantificação do método para o bisfenol A foram, respetivamente, 1 e 5 &micro;g L-1. O coeficiente de determinação (R2) e a recuperação média para o bisfenol A foram, respectivamente, 0,99 e 91,55%. Na segunda etapa desta pesquisa analisaram-se amostras de água coletadas na cidade de Americana para a determinação do nonilfenol e do bisfenol A. Como método de extração dos compostos, usou-se a extração em fase sólida (SPE) e como técnica analítica a cromatografia gasosa acoplada a espectrometria de massas (GC/MS). Os resultados indicaram a presença desses compostos em alguns pontos de amostragem sendo que a concentração do nonilfenol a variou de 5,028 a 10,524 &micro;g L-1 e para o bisfenol A a concentração variou de 5,645 a 295,255 &micro;g L-1. Foram feitos também testes ecotoxicólogicos utilizando como organismo teste o microcrustáceo Daphnia similis, porém o nonilfenol e o bisfenol A, na concentração testada que variou de 0,05 a 500 &micro;g L-1 não apresentaram toxicidade aguda. / In this study it was determined nonylphenol - a xenobiotic compound used in the manufacture of antioxidants, additives for lubricating oils and production of ethoxylated surfactant - and bisphenol A - a chemical compound used in production of various products, such as polycarbonate plastic, epoxy resins and flame retardants. Both exhibit estrogenic activity at concentrations lower than 1 ng L-1 - in five sampling points in the city of Americana, SP. Due to the widespread use of these compounds, they are present in substantial quantities in industrial sewage. The first step of this study was to validate the analytical method following the Method 8270D of the United States Environmental Protection Agency (USEPA) that describes the validation procedure for semi-volatile compounds analized by gas chromatography-mass spectrometry (GC/MS). The limits of detection and quantification for determining the nonylphenol were, respectively, 1 and 5 &micro;g L-1. The coefficient ofdetermination (R2) and recovery for nonylphenol were respectively 0.99 and 99.04%. The limits of detection and quantification for the bisphenol A were, respectively, 1 and 5 &micro;g L-1. The coefficient of determination (R2) and recovery for bisphenol A were respectively 0.99 and 91.55%. In the second step of this study were analized in water samples of Americana city for the determination of nonylphenol and bisphenol A. As a method of extraction of the compounds it was used solid-phase extraction (SPE) and as analytical technique GC/MS. The results indicated the presence of such compounds in some sampling points and the concentration of nonylphenol ranged from 5.028 to 10.524 &micro;g L-1 and bisphenol A concentration ranged from 5.645 to 295.255 &micro;g L-1. Ecotoxicological tests were also performed using as test organism microcrustaceans Daphnia similis, but nonylphenol and bisphenol A, tested at concentration ranging from 0,05 to 500 &micro;g L-1 showed no acute toxicity.

Neste trabalho foi desenvolvida, otimizada, e validada, uma metodologia para análise de 15 pesticidas organoclorados em sedimento através de HS/SPME-GC/MS. Esta metodologia foi aplicada para análise de amostras reais visando à realização de um diagnóstico da contaminação por pesticidas organoclorados do Rio Atibaia, principalmente em sua região próxima a contaminação oriunda da empresa Shell Brasil S.A. unidade de Paulínia. Para realização deste diagnóstico, também foi desenvolvida uma metodologia padronizada para diagnóstico ambiental de áreas contaminadas, embasada principalmente em conceitos de Gestão de Qualidade e Meio Ambiente abordadas nas normas ISO 17025, ISO 14001 e GLP. Finalmente, aplicando a metodologia analítica validada, e a metodologia para realização de um diagnóstico ambiental, foi realizado o diagnóstico da presença de pesticidas organoclorados no Rio Atibaia, indicando a existência de diferentes pesticidas organoclorados em sedimento, com destaque para os compostos DDE e &#61543;BHC que se encontraram em valores acima dos recomendados pela legislação canadense. Os resultados encontrados também demonstraram que as metodologias desenvolvidas foram adequadas para análise de uma contaminação real. / In this work a methodology was developed, optimized and validated for the analysis of 15 organochlorine pesticides in sediment through HS/SPME-GC/MS. This methodology was applied to the analysis of real samples for diagnosis of the organochlorine pesticides contamination of the Atibaia River, mainly in its region close the contamination from company Shell Brasil S.A. site of Paulínia. For accomplishment of this diagnosis, also a standard methodology for environmental diagnosis of contaminated areas was developed, mainly based in concepts of Quality Management and Environmental Management find in standards like ISO 17025, ISO 14001 and GLP. Finally, applying the validated analytical methodology and the methodology proposed for environmental diagnosis, the diagnosis of the organoclhorine pesticide presence in the Atibaia River was performed, indicating different organoclorine pesticides in sediment, mainly DDE and yBHC, which were found in values above of those recommended by the Canadian legislation. The results also demonstrated that the developed methodologies are adequate for analysis of a real contamination.