Zinc (Zn) is a transition metal whose stable isotopes can record information on important oceanographic processes. This dissertation has established an analytical approach for the separation and isotopic analysis of Zn in seawater, and applied it to various seawater samples to trace biogeochemical processes in the oceans. The main analytical challenges in the isotopic analysis of Zn in seawater relate to very low concentrations (< nmol/kg) in a matrix of major elements present at concentrations up to 8 - 9 orders of magnitude higher. These problems have been overcome by a pre- concentration procedure, using Al(OH)3 co-precipitation, followed by further purification and separation of Zn on multiple anion exchange columns. Since Zn is ubiquitous in the environment, it is crucial that the Zn environmental blank contribution is maintained at a low level. The procedural blank has been reduced to max 2 - 3 ng for 4 L seawater samples in this study, which enables the isotopic analysis of most Zn- depleted surface samples. A Zn double spike approach has been adopted, and further developed in this study, for the correction for mass discrimination during the separation and analysis procedure. The double spike approach, and subsequent analyses of Zn samples on MC-ICPMS, were proven successful, with tests on Zn JMC standards yielding δ66Zn = +0.03±0.09%0 (n = 178). The analytical approach has been tested using multiple analyses of samples from a homogenized tank of deep Atlantic seawater, obtaining consistent results of δ66Zn = +0.46±0.08%0 (n = 6) and [Zn] = 2.22±0.04 nmol/kg (n = 6). A few Zn standard addition experiments have been done on the post- eo-precipitation 'Zn free' seawater samples and MQ samples, the results of which further proved the robustness of the double spike approach and the chemical procedure. Data were collected in order to test this new technique, and also to serve as the first substantial dataset available to understand how Zn isotopes are fractionated in the oceans, and how they may be used as a tracer of biogeochemical cycling. Depth profiles of Zn concentrations and isotopic compositions are presented from three different locations in the world's oceans - the subtropical Atlantic Ocean, the Southern Ocean and the Northeast Pacific Ocean, demonstrating the responses of Zn isotopes to biological cycling in two contrasting biogeochemical regimes: trace-metal limited and major-nutrient limited. The new technique has produced nutrient-type Zn concentration profiles which compare reasonably well with previous measurements. Deep ocean Zn isotopic compositions are very homogeneous (at δ66Zn = +0.52±0.10%0), similar to or slightly heavier than those of the continental inputs. In contrast, surface ocean Zn isotopes show pronounced variability, with the largest variations in the trace-metal limited HNLC regions. Overall, Zn isotopes at the surface are controlled by inputs (dust, upwelling, δ66Zn ~ +0.3 to +0.5%0) and preferential removal of the light isotope by phytoplankton (pushing residual seawater δ66Zn up to over +1%0). Anomalously low ()6 Zn values have been found in sub-surface waters (around 40 - lOOm) at all locations studied, but especially the NE Pacific, reflecting either very shallow regeneration of some of the isotopically light Zn taken up by phytoplankton cells at the surface, or preferential scavenging of the heavy isotopes. This dissertation, by developing an effective analytical approach for the separation and isotopic analysis of Zn in seawater and presenting several sets of preliminary Zn isotopic data in the oceans, lays the groundwork for the potential use of Zn isotopes as a marine biogeochemical tracer.

Online monitoring of analytes in marine environments is receiving increased attention for a range of applications, including detection of pollutants in water. Major pollutants in water include volatile organic compounds (VOCs), dissolved gases and other naturally produced or anthropogenic toxic compounds. In addition to being a concern to environmental protection agencies, VOCs are also of interest to the oceanographic and atmospheric community as they are found to be important contributors to climate change, global warming and oxidant formation (smog). One of the well-established techniques for detecting traces of organic compounds in aqueous solutions is membrane inlet mass spectrometry (MIMS). The technique is simple (no need for pre-connection), sensitive (detection limits are in the ppb range) and able to analyse multi-component mixtures simultaneously and in a few minutes. The aim of this research is to investigate, design, produce and test a novel, sensitive, fast, safe, state-of-art membrane inlet probe and couple this to an existing mass spectrometer so as to allow mass spectrometry in harsh or demanding environments as well as using the system for detection of volatile orgamc compounds in aqueous samples or monitoring trace organics in water. In this work, also a novel comprehensive approach for simulating MIMS systems by calculating spectral characteristics of toxic VOCs in water, such as benzene, toluene and chloroform is presented. For comparison to experimental data, MIMS system consists of a membrane sample inlet, coupled to a portable quadrupole mass spectrometer (QMS) system with m/z 1-200 mass range. The QMS is characterized for monitoring analyte concentrations from 1 - 1000 ppm. Using the multi-ion trajectory simulation program QMS-2, developed by the University of Liverpool, the performance of the complete MIMS system including the membrane inlet probe and the QMS were simulated. The simulated results are compared with experimental ones showing good agreement for different analyte concentrations at room temperature.

Shelf seas are highly productive regions of the world's ocean. Contributing 16 - 30 % to global ocean carbon fixation while representing a mere 7 % of the area, their importance in the carbon cycle is disproportionate to their size. This high productivity has econonimical significance, supporting over 90 % of global fishery yields (Pauly et al., 2002). Shelf seas are also physically dynamic regions. On an annual cycle, the water column in shelf seas is fully mixed in winter and thermally stratified in summer in deeper regions, with enhanced mixing along the shelf-edge. In addition, shelf seas act as a buffer between the land and coastal seas, and the open ocean. However, the processes that transform nutrients within the shelf sea are poorly understood. More so, the role of physical processes in both transporting nutrients, as well as their interaction with the biological processes that govern nutrient concentrations and partitioning are currently unresolved. Here, nutrient dynamics, with a specific focus on phosphorus, were assessed within the Celtic Sea, part of the northwest European shelf. The distribution and partitioning of phosphorus between the particulate (PPhos) and dissolved organic (DOP) and inorganic (DIP) phases was determined over various temporal and spatial scales. The concentration of labile DOP (phosphomonoesters, PME) and its rate of turnover were determined using enzyme rate assays. The microbes involved in PME hydrolysis were identified using enzyme labelled fluorescence techniques. The influence of physical processes, including spring-neap tidal cycle, mixing over topography and storm enhanced mixing on the vertical distribution of phosphorus in the water column were also assessed. DOP accumulated in the surface layer of the thermally stratified shelf waters and at the shelf edge. DOP production was enhanced at the shelf edge and during storm events due to enhanced mixing and fluxes of phosphate, which were rapidly shunted into the DOP pool through enhanced primary production. However, during mixing there was a counteracting downward flux of DOP exported to the bottom waters. Profiles of PME concentrations revealed a relatively labile component to bottom layer DOP, which had turnover times in the order of days. Comparison of observations in the Celtic Sea and Porcupine Bank region demonstrated that the accumulation of DOP on the shelf and at the shelf edge relative to the adjacent slope and oceanic regions is a persistent feature of the western European continental margin. Through a number of shelf-edge exchange processes, including wind mixing on short time scales, tidal mixing on fortnightly timescales and seasonal winter mixing, the Celtic Sea was identified as a potential source of DOP to the North Atlantic, where production is thought to be phosphorus limited (Mather et al., 2008).

Recent recognition of the importance of trace metals in oceanic biogeochemical cycling and of the significance o f atmospheric trace metals inputs to marine waters, highlights the need to assess the dissolved trace metals inputs from atmospheric sources. Atmospheric inputs are important to the surface waters of the Eastern Mediterranean, due to the reduction of riverine inputs. High-volume aerosol samples were collected from Haifa, Israel and Erdemli, Turkey in 1996. These samples were characterised by air mass back trajectories, because contrasting aerosol sources (urban and crustal) are apparent in this region. Trace metal (Cu, Pb and Zn) seawater solubility studies were determined for selected samples, under carefully controlled conditions (seawater at pH 8.0 and 25.0 ± 1.0 °C; shaking rate 150 osc min"'). The average seawater solubilities o f Zn and Pb from the northern (predominantly European source) wind sector were statistically higher than the southern (mainly Sahartm and Arabian desert source) wind sector. The total dry deposition fluxes o f trace metals were estimated from the geometric air concentrations of both wind sectors, the wind sector weighting and assimiing a deposition velocity of 0.1 cm s'K Trace metal seawater soluble fluxes were calculated using mean seawater solubilities of the aerosols from the northern and southern wind sectors. The soluble trace metal fluxes, by dry deposition, to the Eastern Mediterranean were compared with soluble wet deposition and riverine fluxes. A novel experimental system was assembled and validated, in order to (i) enhance our knowledge of the physiochemical and biological factors that affect the seawater solubility of trace metals and (ii) to refine the soluble trace metal flux estimates. The experimental system was capable of monitoring trace metal desorption reactions at high temporal resolutions (> 45 s). It was initially applied to the measurement of the extent and rate of desorption of total dissolved and Mabile dissolved' Cu, Pb and Zn from Liverpool urban particulate material, then to the seawater solubility of trace metals associated with urban particulate standard reference material and Saharan dust. In order to increase our understanding of the fate of trace metals associated with aerosol particles after dry deposition into seawater, the effects of bacteria, proportional mbcing of end member aerosols, particle concentrations, mbcing rates, light and temperature on the desorption of aerosol associated trace metals were separately investigated. It was found that the presence of bacteria in seawater and seawater temperature enhanced the seawater solubility of Zn, Pb and Cu. In addition, natural light enhanced the solubility of Cu from Saharan dust. Conversely, increasing the particle concentrations and the mixing rate of the incubated seawater caused a decrease the observed seawater solubility of aerosol associated trace metals (the decrease was greater for Pb and Zn than Cd and Cu).

The molecular level characterisation of compounds comprising the dissolved organic nitrogen (DON) pool is an important task for chemical oceanographers wishing to understand its role in the marine N cycle. Low DON concentrations, problems with saline matrices and a lack of pre-concentration methods have all contributed to DON being ignored and disregarded, until recently. Sub units of DON have been analysed as bulk parameters within which the low molecular weight (LMW; < 1,500 Da) fraction has been proposed to drive regenerated production within the oceans. The largest producers of these compounds are phytoplankton. Dissolved combined amino acids (DCAAs) are proposed to be the largest identifiable component of the LMW fraction. Peptides were chosen as the starting point for this study on DON characterisation, due to their unrivalled detection when analysed via liquid chromatography/ mass spectrometry (LC/MS). A method was developed for the characterisation of low molecular weight peptides, released either actively or passively from the axenically-cultured phytoplankton Phaeodactylum tricornutum. Methods for the separation (high performance liquid chromatography; HPLC), detection (mass spectrometric; MS), de-salination and pre-concentration (solid phase extraction; SPE), of analytes present in the culture water sampled during the period of maximum DON, were developed. The successful chromatographic separation of LMW peptides was achieved using a Phenomenex® Gemini Gig column in conjunction with mobile phases of acidified MeOH and water. The SPE method was developed on a Hamilton PRP-1 column containing a polystyrene divinylbenzene stationary phase (PSDVB). During the extraction process the increased hydrophobicity of the PS-DVB phase was predicted to yield increased recoveries of peptides, when compared to analogous d g phase cartridges. The method was transferred to extraction cartridges (500 mg, StrataX). Further investigations were then carried out into the affects of salt and dissolved organic matter on the extraction process. Samples were prepared by applying the extraction method to 1 L supernatants of culture water samples. The HPLC protocol was used to separate the components of the complex sample prior to data acquisition in both full MS mode and in the data dependent mode (DDMS). Mass spectra and chromatograms of ions unique to the cultured waters were identified. Further instrument manipulation allowed interfering ions to be diverted away from the mass analyser and consequently multistage mass spectrometry (MS²) to be carried out on unique ions that exceeded the threshold intensity of 1 x 105. Unique ions identified in the axenic cultures were two amino acids TYR and a modified structure isomerically/isobarically related to TYR. Seven peptides were partially sequenced. These were H-(VAL, THR, Xxx)-OH, H-(GLN/LYS, ALA, ASN, Xxx)-OH, H-(ASN, ALA, GLU, Xxx)-OH, H-(VAL, GLU, Xxx)-OH, H-(SER, HIS, Xxx)-OH, H- (PRO, XLE,HIS, GLN/LYS, GLY, Xxx)-OH and H-(Xxx, XLE, GLN/LYS, XLE, GLU)- OH. One whole peptide was tentatively proposed as H-TRP-PHE-OH. A significant loss of data was observed between the unique peptide ions identified in the MS analysis and the ions that underwent CID during the DDMS analysis, because they were below the threshold ion count or co-eluted with a more dominant ion. The method development carried out through this study has enabled the successful analysis of samples previously considered incompatible with LC/MS instrumentation. The method can be applied to all aquatic environment samples for both contaminant removal and preconcentration requirements and can be seen as an initial step from which many different avenues of future work may be explored.

No description available.

The core subject of this thesis is to assess the applicability of ocean colour algorithms for deriving chlorophyll and CDaM concentrations in east coast of Peninsular Malaysia waters. A series of bio-optical observations were conducted in the study area during the 2009 seasons. These included in-water constituents (chlorophyll, suspended sediment and CDaM), absorption properties and reflectance. The analysis of the data reveals a clear seasonal signal with high values of all constituents and absorption properties during the northeast monsoon and low - . values during the southwest and inter-monsoon seasons. The timing, magnitude and spatial extent of these changes are associated with seasonal changes in hydrographic conditions (wind forcinq, sea surface temperature and freshwater input). Contrary to the trend during the monsoon seasons, inter-monsoon chlorophyll concentrations were higher offshore with some evidence of the pigment packaging effect. In the blue part of the spectrum, non-phytoplankton material (CDaM and detritus) is a dominant absorber (> 70% of non-water absorption) regardless of the season and this does not always covary with chlorophyll concentration. The performance of standard empirical and semi-analytical ocean colour algorithms at retrieving chlorophyll concentration was evaluated and validated using the bio-optical data in the study area. The results of our analysis showed that both types of algorithm often perform poorly in the study area, either due to a wide range of variation in in-water constituents or uncertainties in the spectral shape and magnitude of inherent optical properties. Using a series of in-situ bio- optical data, the algorithm best-suited for the study area was developed and evaluated. The results of this study indicate that a regionally-tuned chlorophyll algorithm can provide more accurate estimate of chlorophyll concentration provided that there exist a mean relationship between chlorophyll and CDaM, and the spectral shape of absorption does not change with varying environmental conditions. The most consistent result of this study was that absorptions ii by phytoplankton and CDaM can be well estimated by a simple blue-green band ratio, offering a great opportunity to discriminate chlorophyll from CDaM. Time-series of remote sensed distributions of chlorophyll, CDaM, sea surface temperature and wind speed were examined to evaluate variability of physical forcing and environmental conditions on seasonal and inter-annual variations in ocean colour in the study region. The results of this study confirm that the strong seasonal and inter-annual cycles of chlorophyll and CDaM concentrations are related to climatically driven cycles of rnonsoon and physical forcing (wind speed and SST). It is also shown that the annual cycle for both chlorophyll and CDaM concentrations is often overshadowed by inter-annual climate variability.

No description available.

Air bubbles in the ocean, naturally induced by breaking waves or artificially entrained by ships, remain in the water for different periods of time. Knowledge of the factors accounting for the differences in air bubble residence time (BRT) is essential for understanding processes of air sea-gas exchange as well as for the detection of underwater ship wakes in defence applications. Reasons for the differences in BRT have been found mainly with respect to physical and chemical properties of seawater, such as temperature, salinity and gas saturation level. The impact of biological factors on the behaviour of air bubbles in seawater has not previously been investigated. It is hypothesised that phytoplankton influence BRT through the production of dissolved organic material (DOM) and oxygen. Laboratory experiments were carried out in a seawater mesocosm tank system to investigate the influence of phytoplankton growth on the BRT of artificially injected air bubbles of a wide size range (10-1000 µm diameter) using both natural phytoplankton populations from Kiel Firth and phytoplankton monocultures. BRT was determined acoustically and several phytoplankton growth-related parameters (chlorophyll concentration, dissolved inorganic nutrients, dissolved organic carbon (DOC), oxygen saturation, bacteria numbers) as well as physico-chemical parameters (surface tension and viscosity) were monitored. BRT showed statistically significant covariation with oxygen saturation and chlorophyll a concentration during phytoplankton growth periods in the tank. Increases in BRT of a factor of > 2 were found during the chlorophyll maxima, provided that the water was sufficiently supersaturated with oxygen (~>110%). When the seawater was undersaturated with oxygen, BRT changed only marginally regardless of the chlorophyll a concentration. No clear relationship was evident between BRT and measurements of DOC, surface tension and viscosity. Investigations of the influence of dissolved oxygen on BRT through variation of oxygen saturation of deionised water showed that oxygen saturation alone has no apparent effect on BRT. The influence of phytoplankton on the rheological properties of an air/water interface was investigated in small scale experiments using different phytoplankton monocultures. An increase in surface shear viscosity was detected for only one of the four species of microalgae tested, Nitzschia closterium. Dependency of BRT on the combination of oxygen supersaturation and other phytoplankton growth-related parameters are discussed.

Cette étude doctorale a consisté à décrire la dynamique géochimique de deux pockmarks à hydrates de gaz de la marge africaine en considérant deux approches différentes. La première zone d’étude, appelée Preowei, est située au large du Nigéria. Elle est caractérisée par un grand nombre de pockmarks de tailles différentes, plus ou moins proche les uns des autres. Les analyses géochimiques des échantillons de fluides interstitiels, combinées aux données géophysiques (séismiques) ont permis de mieux comprendre le schéma de migration des hydrocarbures pour un ensemble composé de quatre pockmarks très rapprochés. L’utilisation de ces données géochimiques dans un modèle de transport- réaction a conduit à une datation de plusieurs séquences de libération de gaz au sein de ces structures. Un schéma conceptuel décrivant les processus de formation et d’évolution temporelle des pockmarks a été proposé pour synthétiser les conclusions obtenues. Finalement, cette étude a montré que l’ensemble des pockmarks étudiés sont actifs depuis 2700 ans, qu’ils sont en phase de formation d’hydrates pour certains, et de carbonates pour d’autres. La deuxième structure étudiée est le pockmark Regab. Il est situé au large du Gabon, au nord du canyon sous-marin alimenté par le fleuve Congo. Il est caractérisé par la présence d’hydrates affleurant et une faune abondante et très variée sur toute sa surface. L’originalité de ce travail a été d’étudier la distribution de la mégafaune présente sur ce pockmark en fonction de la nature des fluides qui migrent dans le sédiment superficiel, et qui est libérés dans la colonne d’eau. Une attention particulière a été portée au méthane car c’est un élément central dans le cycle énergétique des microorganismes qui vivent en symbiose avec cette mégafaune. Trois nouveaux habitats ont été étudiés. Les données obtenues, associées à celle de la littérature ouverte, renforcent les conclusions des travaux antérieurs. Les Mytilidés ont besoin de très fortes concentrations de méthane pour se développer. Elles colonisent les zones de sortie de bulles et celle caractérisées par des hydrates affleurants. Les tapis bactériens sont associés à des zones où l’oxydation anaérobique du méthane se déroule dans le sédiment superficiel, avec une méthanogenèse dans la couche sous-jacente. Les Vésicomydé polychètes vivent dans des zones pauvres en méthane et sont très sensibles à sa variation de concentration. / The present work describes the dynamics of two pockmark areas, off West Africa. The intention is to propose two different approaches to study the relationships between fluid migration and pockmarks. The first investigated area corresponds to a pockmark cluster called Preowei, located off Nigeria. Geochemical analyses and modeling were combined with seismic data to detail the hydrocarbon migration pattern at this area, with implication on both the pockmark formation and the evolution of their morphology. The proposed interpretation seeks to identify the conceptual bases of pockmark evolution over time at this area. It is argued that the cluster has been active for at least 2700 years, and it is still at the stage of hydrate formation for some pockmarks and carbonate formation for other. The second investigated pockmark, called Regab, is located off Gabon. It is a giant pockmark of 800-m diameter, characterized by an ecosystem rich in fauna, with a large variety of living species. The main core of the work done on this pockmark was focused on finding a link between the fluid chemistry and the spatial distribution of the living communities which populate it. This was achieved by combining new geochemical and bathymetric results with a well-compiled dataset from the literature.