Ship-board experiments in the North Atlantic were used to study how food quality influences the egg production of Calanus finmarchicus feeding on natural planktonic diets. Food quality was expressed in terms of carbon (C), nitrogen (N), and the essential fatty acids eicosapentaenoic acid (EPA; 20:5(n-3)) and docosahexaenoic acid (DHA; 22:6(n-3)). Five consecutive 24 hr bottle incubations were conducted in April and July/August 2002 under in situ conditions to determine egg production rates and the ingested quantities of C, N, EPA and DHA. Biomass contributions towards growth were determined and the biochemical composition of the eggs was examined. In order to accurately determine ingestion rates, a method to account for microzooplankton grazing in particle removal experiments was developed. Balanced physiological budgets were compiled for C. finmarchicus in both seasons. The input terms of these budgets consisted of ingestion and the use of biomass, and the outputs were growth, respiration, excretion and egestion. Respiration and excretion were not determined experimentally, and were therefore determined by mass balance and compared to literature-derived values. In April, close agreement between literature- and mass balance-derived rates of respiration and excretion demonstrated that the experimentally determined components of the budget were accurate. Ingestion rates were low, and > 80 % of the C utilised was derived internally from somatic biomass. The absence of storage fatty acids and the low C:N ratio (~ 4 µg µg-1) of the biomass lost from the females indicated that these animals had been catabolising structural protein and were close to exhaustion. This suggests that when food is scarce, C. finmarchicus adopts a semelparous reproductive strategy. In July/August, the observed growth exceeded the estimated ingestion rates. This shortfall was possibly provided by cannibalising eggs. Assuming that EPA and DHA were used with high efficiency (0.9), the stoichiometric analysis predicted that these compounds were non-limiting in April. Using typical maximum growth efficiencies for C (< 0.6) and N (0.4), the former was predicted to be limiting because the biomass utilised was rich in N, EPA and DHA relative to the demand for C.

The aim of this study is to better understand chemical recycling at destructive plate boundaries. Isotopic, major and trace element data of lavas sampled at varying distances from the trench in the Izu-Bonin arc provide constraints on the different types of flux that influence subduction zone magmas. Geochemical models are employed to quantify the exchange of elements between flux and mantle that lead to the creation of arc magmas. These calculations allow the changes in fluid flux from the slab and the variations of mantle composition to be correlated with the variations in across-arc geochemistry. All of the analysed lavas show arc-related geochemical signatures such as enriched LILEs, depleted HFSEs and fluid-modified strontium isotopes. However, a systematic variation in isotope and trace element ratios is recognised across the Izu-Bonin arc. Radiogenic 87Sr/86Sr and 143Nd/144Nd, low Nb/Y and high Ba/La in the volcanic front suggests melting of a depleted mantle source influenced by an aqueous fluid (AQF). Less radiogenic 87Sr/86Sr and 143Nd/144Nd and higher Th/Ce and Nb/Y in the rear and back arc suggest melting of a more fertile mantle metasomatised by supercritical fluids (SCF). Positive correlations between 87Sr/86Sr and 143Nd/144Nd are observed in lavas sampled across the width of arc. The correlation is also found within some volcanoes found behind the volcanic front (Taga and Hakone). This suggests that magmas affected by AQF and by SCF are tapped by single volcanoes and at least partially mixed prior to eruption. Analysis of chemostratigraphic variations in the Ashtaka, Taga, Hakone, Hachijojima, and Oshima volcanoes reveal that the fluxes are not in a steady state. Individual volcanoes can tap heterogeneous mantle sources and variable fluid input over tens of ka’s. High-precision double-spike Pb isotope measurements provide estimates of the amount of overprinting of the slab fluid isotope signature by the mantle wedge. The effect is greatest along the volcanic front where 70% of the Pb is derived from slab fluids compared to 34% in the back arc. Pb isotopes also highlight that the mantle source is heterogeneous along the arc with Δ8/4Pb and Δ7/4Pb increasing toward the north. The composition of the crust beneath the arc is estimated using the Tanzawa plutonic complex, and is found to be isotopically similar to the northern Izu-Bonin arc. This suggests that crustal contamination will only have a minor effect on the isotopic composition of the arc. The isotopic composition of Tanzawa complex indicates a source resembling the Indian Ocean mantle domain was present in the mantle wedge before 7Ma.

No description available.

Marine dinoflagellates are an ecologically important group of protists within the plankton, performing key process such as photosynthesis, heterotrophy and toxin production. Some dinoflagellates are also capable of producing bioluminescence and they are the most abundant protists that produce light in the surface waters of the oceans. This study employed molecular tools to investigate the identity of bioluminescent species, the genetic basis, diversity and functional regulation of bioluminescence, and the distribution of marine bioluminescent dinoflagellate populations. Using “universal” and taxon specific PCR primers designed to amplify the luciferase gene (lcf), the distribution of this gene within dinoflagellates was found to be taxon specific and the first lcf sequences obtained from four genetically distant genera revealed a previously unknown high diversity of this gene. The luciferin binding protein gene (lbp) was detected for the first time in three genera of ecologically important gonyaulacoid dinoflagellates, showing that this understudied gene is common in dinoflagellate bioluminescence systems. Phylogenetic analyses of both lcf and lbp provided new insight on species divergence within the toxic genus Alexandrium and pointed out important pitfalls in using protein coding genes for phylogenetic studies. The lcf PCR primers were employed in the first field study using a molecular approach to detect natural populations of bioluminescent dinoflagellates, showing that this approach outperforms optical bioluminescence measurements and that their distribution and composition is intimately tied to hydrographic patterns that create distinct environmental zones. The lcf PCR primers were also employed to study the regional variation in bioluminescence of Noctiluca scintillans, showing for the first time that the environment maintains or eliminates bioluminescence, by finding that a hydrographically isolated non bioluminescent variety in the west coast of the USA has “switched off” its bioluminescence system while diverging to possibly become a different species. Also, a novel lbp was discovered in N. scintillans which improved the current model for the evolution of bioluminescence genes in dinoflagellates. This thesis is the first study to employ molecular tools in a comprehensive and multifaceted investigation of dinoflagellate bioluminescence and has contributed significantly to building a fundamental understanding of this remarkable phenomenon.

The marine carbonate chemistry system is the reactions and dynamic equilibria in seawater that involve dissolved carbon dioxide (CO2) and the deprotonated forms of carbonic acid, which are bicarbonate ions and carbonate ions. This system affects other marine biogeochemical cycles and ecosystems through its strong influence on seawater pH. Currently, a rapid chemical perturbation is being driven by the accumulation of anthropogenic CO2 in the ocean, which has taken up a significant fraction of the CO2 emitted to the atmosphere by fossil fuel burning, cement manufacture and land-use change since pre-industrial times. To predict the future consequences, it is first essential to be able to accurately measure the present state of the system, and to understand how it operates. To contribute to these goals, I have firstly made new developments to the measurement techniques for two key system variables, namely total alkalinity and the stable isotopic composition of dissolved inorganic carbon. Secondly, I have combined results from recent research cruises along a hydrographic transect in the Northeast Atlantic with historical datasets in order to quantify the rate at which anthropogenic CO2 has accumulated in the interior ocean over the past three decades, demonstrating that the regional accumulation rate is greater than the global average. I have used model output to assess uncertainties in these results that are caused by spatiotemporal heterogeneity in the distribution of observations. Thirdly, I have carried out a theoretical investigation into the influence of marine calcifying phytoplankton, like coccolithophores, on air-sea CO2 exchange. I have shown that these organisms can behave either as CO2 sources or sinks depending upon their relative rates of calcification and autotrophic production, their nutrient uptake stoichiometry, and local seawater conditions. Finally, I provide suggestions for developments to the work presented in this thesis that might help to overcome some challenges that are likely to face this field of research in the future.

The eco-physiological thresholds controlling the distribution of marine invertebrates are of significance in understanding the evolution of marine diversity. This includes the direction of species radiation throughout the oceans. Range expansions occur as a result of evolutionary adaptations, or through environmentally or anthropogenically driven shifts in distribution. The success of such events is centred around a species ability to adapt; in order for a migration to be successful, all life history stages must tolerate the conditions of the new habitat. This thesis examines the thermal and hyperbaric thresholds affecting range extension in the marine environment. It focuses on the larval development of the shallow-water North Atlantic gastropod Buccinum undatum (Linnaeus 1758). The Buccinidae family consists of a wide range of shallow and deepwater species distributed globally. Improved knowledge on this topic will contribute to our understanding of the adaptations influencing both historical and modern shifts in the distribution of species. The thermal and hyperbaric ranges observed during development indicate B. undatum to have the capacity to develop at both temperatures and pressures outside its current distribution. Thermal acclimation to low temperature was also found to increase pressure tolerance during development. A shift in number of embryos developing and nurse egg partitioning per embryo indicate a decrease in developmental success at temperatures above those it is naturally exposed to. An increase in energetic expenditure, with both increasing temperature and pressure, relates to a rise in the metabolic cost associated with development under either condition. These results, combined with the known life history of B. undatum, suggest range expansion into deep water may be a plausible scenario, but tolerance of warmer conditions remains questionable due to the cold-induced spawning observed in this species. The results of this thesis support theories of high-latitude migrations into the deep sea via cold, isothermal waters, and indeed, suggest polar temperatures may promote the rate at which such range expansions occur. Additionally, the observed metabolic cost associated with development suggests hydrostatic pressure may induce bathymetric limits, which explain patterns observed in reproductive trends, eco-physiological adaptations, and faunal distribution in marine invertebrates throughout the oceans.

Estuaries are important ecosystems which are affected by a large range of environmental factors. It is important to measure, characterise and monitor the ecological status of estuaries, and this is the contribution of this thesis for phytoplankton communities in Southampton Water. The size structure and species composition were investigated during 2002 and 2003, with special attention to nanophytoplankton (cells < 5µm in diameter). The main sampling stations were Empress Dock and NW Netley in both years, and Calshot and Horse Elbow in 2002 only. To aid the interpretation of phytoplankton data, information about prevailing meteorological (air temperature, rainfall, irradiance) and hydrographic (tides, water temperature, salinity, and levels of inorganic nutrients) conditions were also collected. In 2002, Empress Dock was sampled weekly between February and October, and other stations were sampled monthly between May and October. In 2003, Dock and NW Netley were sampled weekly between April and September. Measurements made on the phytoplankton included size fractionated (<2, 2-5, 5-20, >20µm) chlorophyll, photosynthetic pigments by HPLC, cell counts by inverted microscopy, and in year 2003 flow cytometry counts and primary productivity (by oxygen) and Fast Repetition Rate Fluorometer (FRRF). Analyses of the major nanophytoplankton taxa involved oligonucleotide probes using fluorescent in situ hybridization (FISH) techniques. Plymouth Routines in Multivariate Ecological Research (PRIMER) statistical analyses were used to calibrate the environmental parameters and phytoplankton carbon biomass. The phytoplankton populations at the four stations were relatively similar. Maximum values of chlorophyll (chl) and carbon biomass were observed between May and August in both years, with a late diatom bloom in 2002, and a mid summer bloom for various organisms. Phytoplankton (as chl or carbon biomass) distributions for 2002 and 2003 could be divided into four phases associated with irradiance and nutrient level. However, there were rapid chl fluctuations during summer due to different factors, such as water column irradiance, tidal range and flushing rate. PRIMER analyses showed that phytoplankton carbon biomass distribution was associated with seasonal patterns, related to light irradiance water column light attenuation, tidal range and nutrients (N and P). In addition, Si is related to phytoplankton succession, and P to size fraction. The nanophytoplankton generally contributed 35-40% of total chlorophyll and up to 60% in winter at the outer stations. Chlorophyll size fraction measurements at Empress Dock (2002) and NW Netley (2003) showed that increased chlorophyll values are generally associated with fractions greater than 5µm (>5µm) and vice versa, although nanophytoplankton (carbon biomass) size structure was dominated by size 2-5µm followed by picophytoplankton, and flagellates >5µm became important in some samples. Comparison of total and fractionated pigment indicated that chlb and chlc2+3 were highly related to the nanophytoplankton fraction and probably inductive of the importance of Chlorophyta and Chrysophyta.

The Controlled Source ElectroMagnetic (CSEM) method has been developed over the past two decades, to provide information on oceanic crustal structure. The stark contrast between the low resistivity of rock structure saturated with salt water, compared to the high resistivity of oil, has meant that the method is increasingly being adopted by the hydrocarbon industry at the exploration stage. During initial assessment, and subsequent development of oil and gas fields, wells are routinely drilled for a variety of purposes. The boreholes provide a possible means of placing either EMsources or receivers within or beneath the target reservoir. This in turn presents the opportunity of applying CSEM methods, using a combination of seafloor and borehole sources and receivers to improve the characterisation and monitoring of the reservoir. In this thesis, forward modelling is used to test out the various survey configurations, in terms of the improvement Borehole CSEM (BCSEM) affords the appraisal and monitoring of hydrocarbon reserves. The results from 1D modelling have shown that the use of downhole instruments (either source or receivers) increased the amplitude anomalies associated with target layers when compared to conventional CSEM. The edge detection capabilities of BCSEM were tested and it was found that a single downhole receiver and a towed seafloor source produced a significant change in the amplitude of the electric field as the source moved over the edge of the modelled reservoir. The method also returned promising results for 3D bodies, showing sensitivity to small structures that are below the detection threshold for conventional CSEM. There is evidence to support that BCSEM could prove to be a useful 4D tool in monitoring reservoir changes during production. The modelling of a depleting anticline reservoir showed that the anomalies associated with the depletion are at potentially detectable levels.

This thesis explores the nature and ubiquity of iron (Fe) inputs from sediments to the oceans. In the last 10 years continental shelf sediments have become widely recognised as important vectors for dissolved Fe inputs to the oceans, where bacterial dissimilatory Fe-reduction (DIR) promotes the flux of Fe to the water column during the oxidation of sedimentary organic matter. Deep-sea and volcanogenic sediments however, are important reservoirs of Fe, which have not yet been investigated as sources of Fe to seawater. Furthermore knowledge of the nature of Fe phases involved in sediment, porefluid and seawater cycling is limited. The nature of Fe cycling was investigated in deep-sea volcaniclastic surface-sediments (0-20 cmbsf). Pore-fluid and sediment samples were collected from tephra-rich sites near the active volcanic island of Montserrat, Caribbean Sea, and mixed biosiliceous sites around the dormant Crozet Island archipelago, Southern Ocean. Analyses reveal both regions maintain high pore-fluid Fe concentrations close to the sediment surface (up to 20 μM 0-5 cmbsf), despite relatively low organic carbon supply and contrasting oxygen utilization pathways. The oxidation of young tephra is thought to maintain the steep oxygen gradient measured in Montserrat sediments, and is considered to be an important component of Fe, and in particular manganese (Mn), cycling with local bottom water. Unlike Montserrat dissolved Fe and Mn in Crozet pore-fluids are dominated by colloidal phases (0.02-0.2 μm), and in both oxic and sub-oxic sediment layers. Thus mixed biosiliceous-volcaniclastic sediments are shown to host important colloidal-Fe generating reactions, which it is argued, promote the exchange of Fe with the overlying bottom waters. Re-cycling processes close to the seafloor are likely to determine the impact of this flux on seawater Fe budgets. Low-cost ex-situ incubation experiments were used to measure a benthic Fe flux on sediments from the river-dominated Californian margin (6.3 ± 5.9 μmol Fe m-2 yr-1) consistent with previous studies. Fe and Mn fluxes from Montserrat tephra deposits were also assessed; Differences in oxidation kinetics are shown to prevent the accumulation of Fe, yet permit the accumulation of Mn (~27 μmol m-2 yr-1) in Montserrat bottom waters. Studies indicate temporospatial variations to bioirrigation and sediment re-suspension are important aspects of sedimentary Fe inputs that are poorly represented by conventional sampling methods. In an effort to trace the biogeochemical processing of pore-fluid Fe in Crozet sediments, its isotopic composition was determined, representing the first measurements of their kind in deep-sea pore-fluids. Unique relative to previous studies of pore-fluid Fe isotopes, the near-crustal δ56Fe compositions, demonstrate that DIR does not impart the same light Fe-isotopic signature that characterises previous sub-oxic pore-fluids. Comparison of reactive Fe contents between Crozet and pacific margin sediments indicates pore-fluid Fe isotopes reflect the extent to which Fe is recycled by redox processes. This discovery brings to light the potential for Fe isotopes to trace the input of Fe from shelf sediments, where redox re-cycling of Fe is extensive. The mean oceanic Fe isotope composition (δ56Fe) is predicted to be -0.1 to -3.2‰ depending on the balance of uncertainty in input terms. The predicted surface water Fe isotope composition in the Crozet region (-2.0 to - 2.2‰) is shown to reflect the light composition of shelf-derived Fe for a Fe inventory already constrained for this region.

Trace elements in marine biogenic carbonates may be used as proxies for past ocean chemistry provided that there is an established relationship between the trace element proxy and a parameter of interest, this relationship is preserved within biogenic carbonate, and the trace element can be determined sufficiently accurately. Successful application of any trace element proxy requires both development of the analytical methodology to ensure accurate data with the necessary sensitivity, and an understanding of the relationship between proxy and seawater chemistry. Herein I develop methods for the determination of Mg/Ca, Sr/Ca and Cd/Ca in planktonic foraminiferal calcite, using inductively coupled plasma optical emission spectrophotometry and isotope dilution thermal ionisation mass spectrometry, and propose a potential reference material for Mg/Ca in foraminiferal calcite. The developed techniques are applied to an investigation of the Mg/Ca temperature proxy over Chatham Rise in the Southwest Pacific Ocean and a calibration study of the partition coefficient, DCd, for cadmium incorporation into planktonic foraminifera. Comparisons of planktonic foraminiferal Mg/Ca, shell weight and oxygen isotope records from sites north and south of the Subtropical Front on Chatham Rise, demonstrate the effects of hydrography, foraminiferal habitat and dissolution as controls on Mg/Ca. Determinations of Cd/Ca in seven species of planktonic foraminifera confirm that the dominant controls on Cd/Ca are foraminiferal habitat and hydrography, with only a minor influence of post depositional dissolution. The major uncertainty in determination of DCd from core top samples comes from uncertainty in estimation of the depth distribution and seasons of calcification of planktonic foraminifera.