The Lumwana Cu±Co deposits Malundwe and Chimiwungo are examples of pre-Katangan mineralized basement that are located in the Domes Region of the Lufilian Arc, an arcuate North neo-Proterozoic fold belt, which hosts the Zambian and Congolese deposits that make up the Central African Copperbelt. The Lumwana deposits are situated within the Mwombezhi Dome; a Mesoproterozoic basement inlier consisting of highly sheared amphibolite grade schist to gneiss units that host the Cu±Co mineralization. Kinematic indicators such as s-c fabrics and pressure shadows on porphyroblasts suggest a top to the North shear sense. Peak metamorphism of 750ºC ± 25ºC and 13 ± 1 Kb indicated by whiteschist assemblages occurred during the Lufilian Orogeny at ~530Ma, with burial depths of ~50km. A major decollement separates the high pressure mineral assemblages of the basement from the lower pressure mineral assemblages of the overlying Katangan Supergroup. The age range and lithologies of the pre-Katangan basement of the Domes Region is similar to the pre-Katangan basement of the Kafue Anticline, which underlies the neo-Proterozoic Zambian Copperbelt deposits situated 220km to the SW. The origin of the protolith to the mineralization is ambiguous at Lumwana with transitional contacts from unmineralized quartz-feldspar±phlogopite basement gneiss to Cu±Co mineralized quartz-phlogopite-muscovite-kyanite-sulphide Ore Schist. The transitional contacts and structural controls on mineralization has led to the hypothesis that these deposits represent metasomatically altered, mineralized and sheared basement, rather than mineralized neo-Proterozoic sediments with amphibolite grade metamorphism. This hypothesis is supported by petrographic analysis, stable isotope analysis (δ34S), whole rock geochemistry, and electron microprobe analysis of ore and host rock assemblages. The transitional contacts observed at Lumwana are due to an alteration event associated with mineralization that removed feldspar from ore horizons resulting in depleted Na and Ca and relatively higher Al components. Sulphides are deformed by the S1 fabric and overprinted by kyanite which formed at peak metamorphism. This indicates that copper was introduced to the basement either syn or pre-peak metamorphism. Post S1 metamorphism with associated quartz-muscovite alteration has remobilized sulphides into low strain zones and pressure shadows around porphyroblasts. δ34SSULPHIDES give values of +2.3 to +18.5‰ that fall within the range of values observed in the Copperbelt of -17 to +23‰. The mechanism of ore formation at Lumwana was dominated by thermochemical sulphate reduction (TSR), indicated by the relatively heavy δ34S values and the absence of the light bacteriogenic δ34S values observed in the Copperbelt. Electron microprobe data of muscovite, phlogopite and chlorite show little variation between early and late mineral phases indicating that metamorphic homogenization of silicate assemblages occurred. The Lumwana deposits are large mineralized shear zones within the pre-Katangan basement. Various styles of basement mineralization are also observed in the Kafue Anticline and the structural controls on mineralization and lithological similarities to the Lumwana deposits suggests that pre-Katangan basement is a viable source for the Cu-Co budget of the Central African Copperbelt and that basement structures had a key role in its formation.

Rifting is the process that leads to the formation of oceans. Rifting is the break up of continents, leading to the formation of new oceanic floor between the two continental plates. Although the concept of continental rifting is accepted within the scientific community, it is still debated what controls the volume and composition of igneous material generated at these constructive plate boundaries. Here I present the results of dynamic modelling of rifted margins. I have explored the consequences of margin and mantle structure on the melt generated during continental extension and breakup. The central aim is to understand how melting affects the rifting of continents, especially in the North Atlantic. In order to understand the enigmatic melt production observed around the North Atlantic various tools are developed for interpreting the model output. These are predictions of primary major element composition of the melt, rare-earth element composition of the melt, predictions of the crystallised mid-oceanic ridge basalt composition and the seismic velocity of the lower crust. The thickness of the lithosphere has a very large impact on the subsequent rifting style. Extension of a 125 km thick thermally and rheologically defined lithosphere that has no prior thinning produces little melt during breakup. The Southeast Greenland margin rifted above a pre-thinned lithosphere and at initial fast half spreading rates. Further- more, to generate the thickness, chemistry and seismic velocities observed off this margin, rifting was coincident with the arrival of a 50 km thick, 200 ◦C thermal anomaly. This thermal anomaly is not a plume, rather an exhaustible thermal layer that has drained along the sub-lithospheric topography from a distal plume. The melts generated are high in MgO, and depleted in TiO. They are depleted in rare-earth elements. This would lead to high seismic velocities within the underplate being, as observed off Southeast Greenland.

The biological carbon pump (BCP) is a significant part of the global carbon cycle, exporting ∼10Gt of particulate organic carbon (POC) out of the euphotic zone each year. However, most of the exported POC is remineralized biologically within the upper few hundred metres of the mesopelagic, above the permanent thermocline. Gaining more understanding of the factors controlling the BCP is hence important for understanding and predicting the global carbon cycle better. This thesis investigates the BCP in the Iceland Basin, and during an artificial ocean iron fertilisation experiment in the South Atlantic. In the Iceland Basin, export during a spring diatom bloom was tracked using Lagrangian sediment traps and thorium-234 disequilibria. A large pulse of diatom detritus was exported suddenly at the end of the bloom, probably upon impending Si-limitation. The particles were rich in transparent exopolymer particles (TEP, sticky polysaccharides secreted by phytoplankton), and a comparatively large proportion (20–40%) of the exported POC sank past 750 m. This shows that diatom blooms can produce rapid pulses of particle sedimentation that are transferred efficiently through the mesopelagic, and suggests that aggregation and sinking are mediated by TEP. In contrast, alleviating iron limitation in low silicic acid waters of the South Atlantic with very high copepod grazing pressure only caused a modest phytoplankton response and no enhancement of downward particle flux. This was probably primarily due to grazing control and detritus-feeding by copepods, since diatom growth rates were apparently not strongly Si-limited. This suggests that future Fe-fertilisation experiments must investigate the role of zooplankton thoroughly to distinguish beween bottom-up control of export by nutrient concentrations and top-down control by zooplankton. Export measurements based on thorium-234 disequilibria compared well with net community production measured by O2:Ar ratios over the 39d experiment, suggesting that these two methods can be meaningfully compared over ∼month-long cruises. Further work was conducted with a mesoscale array of four time-series sediment traps deployed for eight moths in the Iceland Basin to study particle flux at 2000m. Large, fast-sinking acantharian cysts contributed up to 48% of POC flux during a specific flux event in early spring, demonstrating that the celestite shells of these protists do not necessarily dissolve in the upper mesopelagic as generally believed. The hypothesis is advanced that deep sinking of acantharian reproductive cysts during spring in this region enables juveniles to feed off seasonally sedimenting phytodetritus in the deep-sea. Finally, the full time-series of particle flux in the four deep traps was analysed. Fluxes peaked in late spring and again in mid-summer. Over the eight months, cumulative mass flux varied by 30% between traps without corresponding variation in the cumulative flux of thorium-230, implying genuine mesoscale variability in bathypelagic particle flux. Moreover, during any one of the two-week collection intervals total mass flux of particles varied 2–16-fold between traps, although it is unclear how much of this short-term variability was due to differences in collection efficiency between traps. Overall, the traps probably under-collected thorium-230 in absolute terms by at least 50%, but this estimate is very uncertain.

This study assessed the interaction of coastal defence structures (CDSs), namely shore-parallel ‘low crested breakwater structures’ (LCSs), design features and hydrodynamic regime on the quantity and timings of macroalgae deposition. The employed sampling strategy comprised a spatially and temporally stratitified approach of time-lapse photography of macroalgae deposition, verified with field observations. Field surveys determined the associated ecological assemblages of the sediment infauna and rocky shore epifauna associated with the breakwater scheme, as well as for two nearby beaches with groynes. Further analysis determined decay rates, decay processes, changes in C and N stable isotope values of dominant macroalgal species and the dependence of the faunal assemblages on the decaying macroalgae deposits. Temporal analysis highlights the main factors driving macroalgal deposition were differences in spring and neap tidal range, wave height and sea temperature. Greatest deposition occurred during months of lower wave height and fewer storms, when filamentous red algae and ephemeral green algal species dominated. Results indicated to greater amounts of macroalgae deposits around LCSs than around wooden or granite groynes. Beach elevation best explained the spatial variation, both vertically and horizontally, in the benthic assemblages within the breakwater scheme, with the abundance of detritivorous deposit feeders being significantly correlated with abundance of macroalgae deposits. Orientation of LCSs, relative to wave action, was an important driver of epifaunal assemblages on the CDSs, with the eastward ends of the breakwaters providing the optimum intermediate environment with regards to wave action, exhibiting the greatest abundances of epifauna. Stable isotope analysis showed that the carbon and nitrogen isotopic values of macroalgae changed during the decomposition and were both species and time dependent. Isotope analysis illustrated that decaying macroalgae deposits were of greater trophic importance to species within the LCS ecosystem where there was large macroalgal deposition, than to species within the groyne ecosystem where macroalgal deposition was lower. Key findings of the study illustrate the importance of decaying macroalgae deposits for the local ecosystem via modification of food chain energy flows. Though the ecosystem benefits from this allochthonous resource, deposits may be a nuisance requiring controlled human intervention.

The evolution of extensional processes at continental rift zones provides important constraints on the underlying lithospheric deformation mechanisms, level of seismic hazard and location of likely hydrocarbon traps. The Corinth rift in central Greece is one of the few examples that has experienced a short extensional history (< 5 Myr), has a relatively well–known pre–rift structure, is experiencing pure extension, and is located in a fluctuating marine–lacustrine setting producing characteristic cyclical stratigraphy. Traditionally, the rift has been described as an asymmetric half–graben controlled by N–dipping faults on the southern margin. This view has been challenged by increasing seismic data from the off-shore part of the rift which show it is more complex, analogous to more developed rifts like the East African rift and Red Sea. High resolution and deep penetration seismic reflection data across the entire offshore rift zone are combined with onshore geomorphological data to constrain: the architecture of major rift–bounding faults; basin structure; spatial and temporal evolution of depocentres; total extension across the rift; and slip rates of major faults from stratigraphic analysis and dislocation modelling of long term deformation. Stratigraphy within the offshore Corinth rift is composed of a non reflective older unit (oldest syn–rift sediments are ca. 1–2 Ma) and a well stratified younger unit separated by a ca. 0.4 Ma unconformity. Net basement depth is greatest in the present centre of the rift zone (2.7–3 km) and decreases to the east and west (1.5–1.6 km). The 0.4 Ma unconformity surface records an important change in rift geometry. Pre. 0.4 Ma, sediment deposition occurred in 20–50 km long isolated basins, controlled by both N and S–dipping faults. Post 0.4 Ma, sediment deposition and basement subsidence has been enhanced in areas between these originally isolated basins creating a single 80 km long central depocentre. Since 0.4 Ma activity has became focused on mostly N–dipping faults. However, in the west, N tilting stratigraphy and basement indicate S–dipping faults are locally structurally dominant. Late Quaternary averaged major fault slip rates are 3–6 mm/yr on the N-dipping south margin faults, >1.8 mm/yr on S–dipping offshore faults, and 1–3 mm/yr on faults in the eastern rift. Total extension over rift history (Late Pliocene to present) has been greatest in the west (8 km), with extension distributed over many faults (most now inactive) spaced at 5 km intervals. To the east total extension is reduced (5–6 km) and is distributed over fewer faults spaced at 15–35 km intervals. There are large differences in rift character along the rift axis and throughout rift history. The highest geodetic rates over the last 10–100 years are in the western part of the rift and do not correspond to the area of greatest offshore basement depth. This suggests a recent change in the locus of strain focusing, potentially analogous to the change that occurred in rift geometry ca. 0.4 Ma.

No description available.

Marine monopiles can suffer from removal of sediment around their foundations by waves and currents, a process termed scour, which can negatively affect structure stability and integrity of associated infrastructure. Scour is a function of the interaction of local hydrodynamics with the geotechnical properties of the seabed, the feedbacks of which are not well understood. Using the largest prototype scour data base available to date, assembled from field data routinely collected during the consents and design phase of wind farms, this study aims to offer a detailed characterisation of marine monopile scour and conduct critical testing of the current, experimentally-derived, state-of-the-art knowledge and practices. Scour research has been hampered by a dearth of prototype scour observations and much of the existing knowledge is derived from physical and numerical work which has had very little validation with field data. This study addresses the dearth of prototype scour analysis and by adding observations from 281 monopiles more than doubles the size of the currently existing knowledge base on marine monopile scour. Furthermore, the scope, variety and quality of data available in this study have enabled a wider-ranging and more in-depth and problem-focussed analysis of scour to be conducted. The data used in this study comes from a "natural offshore laboratory", consisting of three offshore wind farms in the Outer Thames Estuary, which were strategically chosen to minimise the flow variability within the data set in order to focus on identifying and quantifying the controls on scour exerted by the sea bed substrate. The effect of geotechnical conditions on scour is, so far, little understood as most scour research has focused on unconsolidated sandy sediments. Nevertheless, scour experiments in cohesive substrates have revealed the great complexity of the scour response in such materials. For this reason, quantitatively scrutinizing prototype scour in various substrate types and attempting to establish causal links between geotechnical properties and scour development from real data is important. In order to fulfill the remit of this study, the research is guided by a set of questions, derived from a review of the current scour framework, which pose testable hypotheses and identify knowledge gaps which will be evaluated throughout the course of the analysis. The outcomes of the study include an extensive quantitative description and contextualisation of observed scour with existing prototype observations, a critical validation of current knowledge and methods and an investigation of hydrodynamic and geotechnical controls on scour. Some key findings include improved predictive models for scour depth based on mean water depth as well as secondary relationships for lateral extent and scoured volume. For scour in consolidated and cohesive materials, equations for the estimation of scour-limiting material strength as a function of erosion depth are also proposed. The study concludes with a discussion of temporal, survey resolution and geotechnical issues and recommendations for optimised field data collection and survey strategy, alongside suggestions for additional research to fully resolve some of the findings of this research.

Bubbles, formed by breaking waves, play an important role in the transfer of gases between the Earth’s oceans and atmosphere and have been shown to increase the flux of gases during periods of heightened sea state. Having been formed, these bubble clouds evolve through the effects of buoyancy, gas exsolution and dissolution, and the fragmentation and coalescence of bubbles. A number of experimenters have successfully measured sub-surface bubble clouds using a variety of acoustic and optical techniques, although data over a wider range of bubble radii are required for fuller comparison with models of how these clouds evolve and contribute to air-sea transfers of mass, momentum and energy. This study details the design of an acoustic system deployed on an 11 metre spar buoy during two sea trials in the Atlantic Ocean. Through the measurement of the additional attenuation due to bubbles, bubble size distributions were inferred over the broadest range of bubble radii ever measured using active acoustics in the open ocean. The volumetric backscatter strength from the bubble clouds were also measured to gain a profile of these bubble populations. A gas transfer model was then developed, with the measured data used as an input to calculate the associated fluxes. With this method, bubble-mediated transfer velocities and equilibrium supersaturations were found for the first time based on experimental work. These parameters aid the characterisation of air-sea gas transfer and therefore help improve the accuracy of existing climate models.

The aim of this project was to determine whether otolith trace dement chemistry can be used [Q track migrations in fully marine fish. This question was addressed through a semi-controlled experiment where Irish Sea and North Sea plaice (Pleurononectes platessa) were maintained in a monitored environment. The relationships between water, blood and otolith chemistry were assessed and with reference to environmental and physiological variables and through comparisons of otolith trace clement chemistry in wild plaice tagged by data storage tags (DST).

Samples for the analysis of dissolved Mn, Co, Fe, Pb, Cu, Ni, Cd, Zn, nitrate plus nitrite, silicon and phosphate were collected at 7 stations in the northern and 6 stations in the southern Aegean Sea, eastern Mediterranean, in both March and September 1997. This represents the first extensive dissolved trace metal data set for this region. Additional samples were collected near hydrothermal vents in Milos, and across the Thermaikos Gulf. Trace metal distributions and concentrations were interpreted with respect to the particularly complex hydrography and circulation patterns of the Aegean Sea. The results show elevated surface concentrations of Mn, Co, Fe, Pb, Cu, Ni and Zn which can be attributed to both atmospheric deposition in the southern Aegean and a combination of atmospheric deposition, the outflow of the Black Sea Water and potential coastal inputs within the northern Aegean. Spatial and temporal metal variability in surface waters was observed, with higher concentrations for all metals in the northern Aegean due to additional surface sources. In September 1997 the overall higher concentrations of Mn, Co, Pb, Cu, Ni and Zn are attributed to the shallowing of the thermocline located at approximately 100 m in March to around 50 m in September, although the possibility of enhanced aolian deposition is not excluded. Elevated signatures of dissolved Mn, Co, Fe and Pb are associated with Black Sea Water and, to a lesser extent with Levantine Intermediate Water in the northern Aegean for March 1997. In the more complex hydrography of the south Aegean the elevated dissolved nitrate plus nitrite and silicon are associated with an intrusion of Transitional Mediterranean Water. In addition, dissolved trace metal results from Thermaikos Gulf and Milos do not suggest a significant input of metals from these sources into the Aegean Sea during the period of sampling. Atmospheric metal fluxes for the central and north-western Mediterranean Sea were used to calculate the residence times in the Aegean surface waters. These fluxes were compared with metal fluxes from sediment traps and particulate metal data in the northern and southern Aegean during the period of sampling. Linear regression analysis was applied to Black Sea influenced surface water waters in the northern Aegean in order to estimate the concentrations of Mn, Co, Fe, Cu and Ni in the Straits of Dardanelles. For the metals Mn, Fe and Pb the calculated short residence times in southern Aegean surface waters of 0.3 to 6.0 years reflect their high particle reactivity and scavenging onto particles and transport to depth. Co exhibits a similar cycling pathway to Mn but with longer surface residence times of 4 to 40 years. The vertical distributions of Ni, Cu, Cd and Zn do not resemble those of nutrients. Ni, Cu, and Zn exhibit surface elevation in the northern Aegean, and to a lesser extent in the southern Aegean, whereas Cd depth profiles were found to be homogenous. These profiles are the result of surface metal sources combined with the oligotrophic nature of the Aegean Sea. The present work suggests that the Aegean Sea, as well as the Mediterranean is not in a steady state with respect to Ni, Cu, Zn and Cd. Concentrations in the southern Aegean are overall comparable to recent high quality observations in the open Mediterranean. However, there appears to be an increase in dissolved Cu and Ni from the western to the eastern basins of the Mediterranean Sea due to continuous inputs to surface waters.