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Hydrothermal circulation is a fundamental process in the formation and aging of the ocean crust, influencing its structure, physical and chemical properties, and the composition of the oceans and the mantle. The impact of hydrothermal circulation on mid-ocean ridge processes depends on the composition and volume of circulating hydrothermal fluids, and the extent of partitioning between high temperature axial- and low temperature ridge flank- systems, but these processes remain poorly constrained. This study uses whole rock and secondary mineral chemistries of altered ocean crust to (i) assess the extent of fluid-rock exchange during hydrothermal circulation, and (ii) determine the compositions of axial and ridge flank hydrothermal fluids. Sub Antarctic Macquarie Island is a unique sub-aerial exposure of a complete section of ocean crust in the ocean basin in which it formed. Sr and O isotope analyses from Macquarie Island, combined with stratigraphic reconstructions provide the first isotopic profiles through a complete section of normal ocean crust. Tracer transport mass balance calculations indicate that a timeintegrated fluid flux of 4 ± 1 x 106 kg/m2 is required to produce the observed shift in Sr-isotopic composition. This can be supported by the available mid-ocean ridge magmatic heat and is similar to estimates for sections of in situ ocean crust, but a factor of 10 lower than estimates for ophiolites indicating a fundamental difference between the hydrothermal cooling of mid-ocean ridge and supra-subduction zone ocean crust. Heat flow studies indicate that hydrothermal circulation persists for tens of millions on the ridge flanks, with approximately two-thirds of hydrothermal heat loss occurring off-axis at significantly lower-temperatures than in axial hydrothermal systems. Consequently a much larger volume of fluid is required and only small deviations in fluid compositions may result in significant contributions to ocean chemical budgets. Direct sampling of in situ basement fluids is extremely difficult, and can only be applied to active systems. Here, methods to calculate the compositions of ridge flank fluids from the compositions of secondary mineral precipitates are presented and applied to basalt-hosted calcium carbonate veins. Veins from the eastern flank of the Juan de Fuca Ridge record a temperature dependent fluid evolution, similar to that of near-basement pore fluids sampled by borehole studies. Carbonate veins from the Juan de Fuca Ridge and Ocean Drilling Program Site 1256 record a sufficient decrease in the fluid Sr-isotopic composition with temperature to balance the global ocean Sr budget, however, this result cannot be reconciled with the observation of Davis et al. (2003) that the studied ocean crust has exchanged insufficient Sr with the oceans to balance the global Sr budget. This suggests that these areas cannot be typical of the ocean crust as a whole.

No description available.

This thesis uses data collected between 2007 and 2010 in an intensive, effort-based visual monitoring survey in southwest Cornwall, UK. The survey was carried out from a strategic watchpoint overlooking a regionally unique seabed feature, the Runnelstone Reef, which has previously been identified as key site for all three of the study’s target species: harbour porpoise Phocoena phocoena, basking shark Cetorhinus maximus and Balearic shearwater Puffinus mauretanicus. The location of the survey site is perceived as a productive, coastal marine ‘hotspot’ by local wildlife observers, eco-tour companies, conservation bodies and commercial fishermen. The aim of the study was to use a multidisciplinary approach to investigate the drivers behind the increased abundance and diversity of mega-vertebrates at the site. A wide range of environmental data, from fine-scale bathymetry to remote-sensed oceanographic data, were utilised in an attempt understand the potential interactions between the target species and the environment at a variety of scales. Although the target species have very different ecologies and each represent a different taxonomic Class; they each face significant threats throughout their range due to human impacts and are all listed as species of conservation concern on a number of UK, European and International Directives and Conventions. Therefore, improving our understanding of their distribution and highlighting interactions between the animals and their environment is an important objective, both for science and conservation. Harbour porpoise sightings showed significant fine scale temporal clustering associated with tidal flow, as well as spatial clustering around parts of the survey area with steepest seafloor slopes. The timing and location of highest porpoise densities coincided with tidal-topographically controlled hydrodynamic features identified using fine-scale current profile data (ADCP). The sightings and acoustic monitoring (C-POD) data both showed a high amount of temporal variability at seasonal, daily and hourly scales, highlighting the complex nature of the fine scale animal-environment interactions. Daily patterns in basking shark sightings data were investigated as a function of physical environmental covariates, with particular focus on the effect of meso-scale thermal fronts. In line with previous national scale studies of the species, shark sightings were significantly affected by sea surface temperature (SST) and there was evidence for a change in seasonal abundance compared to the long-term pattern. In addition, the variance of SST over the preceding weeks was identified as being a key predictor of the abundance of sharks in the survey area. Surprisingly, there was not a significant effect of the presence, persistence or thermal gradient strength of fronts on daily shark sightings. The implications of this result are discussed with reference to results of previous studies and the focus of marine protected area policy in the UK. The broad scale spatio-temporal analyses of Balearic shearwater sightings data from the UK, Ireland and France indicate that the birds continue to be recorded in significant numbers throughout areas previously considered to be at the northernmost extent of their range. Record counts of passing birds were recorded off southwest UK in the last two years, along with unprecedented aggregations in bays along the Brittany coast, comprising approximately 20 % of the estimated global population. The data presented provide much-needed quantitative information on the at-sea distribution and behaviour of this Critically Endangered species during the interbreeding period, and support earlier studies suggesting a northwards shift in their migratory distribution.

No description available.

This research explores the potential of the submerged Palaeolithic archaeology of the southern North Sea for answering questions about how hominins occupied and adapted within their environments in these northerly latitudes throughout the Pleistocene. Recent coastal discoveries in East Anglia have demonstrated occupation as far back as ~1 million years, and yet our appreciation of the how, why and who of this occupation is missing a crucial piece of its puzzle; excluding these now-submerged landscapes is an active bias on our understanding, truncating the archaeological record. Having been subjected to repeated glaciations, trans- and regressions, the very processes that led to the terrestrial exposure of these areas have subsequently led to their neglect: the assumption that pre-LGM deposits will have been eroded or re-worked has prevailed. Recent work, however, has demonstrated the inaccuracy of this assumption, with evidence for extant Pleistocene-age deposits, landscape features and archaeology. Unlocking the clear potential of these submerged landscapes now relies on the approaches that we take to their investigation as, to-date, all archaeological finds have been entirely by chance. In order to move beyond this reactive style of archaeology, methodologies must be developed which tackle these areas in a more focused and reasoned way. The research undertaken throughout this PhD makes steps towards this. Starting from no baseline understanding of the nature of the existing resource, this work located, collated and analysed a prolific collection of 1,019 faunal specimens. Recovered by the 19th and 20th Century UK trawling industry, the development of historical methods has elucidated their locations and conditions of collection. Combining this locational information with species taxonomic evolution, the emergent spatio-temporal patterns provide a fresh understanding of the integrity of the extant deposits and unique opportunities for locating them on the seabed. These results are presented at a range of scales: • First, a broad-scale understanding of offshore regions across the southern North Sea which have demonstrated a dominance of cold-stage species from MIS 8-MIS 2. • Secondly, a local scale: linking faunal remains with seabed features in the near shore area off Happisburgh, identifying Early and early Middle Pleistocene assemblages related to exposures of the CFbF. • Finally, a discrete, high resolution area of seabed off the coast of Clacton has been identified. Through the collection of swath bathymetry, this area has shown the exciting correlation of Pleistocene seabed deposits and faunal remains. This research presents a significant move towards a proactive approach to these submerged landscapes and represents a step-change in our ability to understand, locate and engage with this undervalued archaeological resource.

Organisms occupying an environment where change is occurring must move, acclimatise, or adapt in order to prevent extinction. Despite recent evidence, the potential for species to change their distribution range across depths is regularly overlooked as an alternative to well documented latitudinal shifts. The aim of this thesis was to investigate the physiological viability of bathymetric range shifts by assessing the impacts of elevated hydrostatic pressure (HP) and changing temperature in two marine ectotherms: the shallow-water caridean shrimp Palaemonetes varians; and the continental slope-depth anomuran crab Lithodes maja. Gene biomarkers were characterised in both species and their transcriptional regulation was assessed by qPCR. Acute and long-term exposures revealed that elevated HP produced significant perturbations at the transcriptional level in P. varians, and were corroborated by measurements of behaviour and respiratory response. HP-associated pathologies were exacerbated by decreasing temperature, and ameliorated by increasing temperature. Results gave a novel insight into the hierarchy and kinetics of HP-induced stress responses, and suggested that the combination of HP and temperature, in part, determines the physiological limitations to bathymetric migration in shallow-water ectotherms. To further test the role of HP and temperature in setting depth distribution limits, gene biomarkers were characterised in a continental slope-depth crab Lithodes maja. Transcriptional regulation and respiration rate was quantified throughout larval ontogeny, and in mature adults. Early life stages showed HP tolerance beyond that of the species natural distribution limits. The observed HP tolerance window reduced through ontogeny. Reductions in HP tolerance with life stage may be analogous to established thermal tolerance reductions with ontogeny. Further, sustained HP exposures suggest that bathymetric range limits in L. maja are constrained by increased metabolic costs, nervous system sensitivities, and macromolecular damage under elevated HP. HP and temperature, and particularly the combination of the two, play an important role in setting the depth distribution limits of marine ectotherms. For temperate shallow-water adapted marine ectotherms, water temperatures towards the upper limit of their thermal scope may facilitate bathymetric range shifts, whilst colder waters further exacerbate the negative physiological effects of elevated HP. Bathymetric range shifts may, under certain scenarios, offer an important, yet underestimated, alternative to latitudinal shifts in light of contemporary climate change. Further, the combination of HP and temperature may have played an important role in the colonisation of the deep sea from shallow waters by marine ectotherms.

Marine dinoflagellates are an ecologically important phytoplanktonic group that accounts for two thirds of all known harmful algal bloom (HAB) species. This study explores the population ecology of Lingulodinium polyedrum (F. Stein) J.D. Dodge, a common bloom-forming dinoflagellate species in Southern California. Lingulodinium polyedrum is not considered a HAB species, but functions as one of the main model organisms for dinoflagellate biology. As such, knowledge about this species also contributes significantly to the understanding of dinoflagellate population dynamics at a more general level. In an attempt to understand some of the complex interactions that govern L. polyedrum population ecology, laboratory experiments of life cycle control and intraspecific phenotypic diversity were linked with an in situ study of the population dynamics and the intraspecific genetic diversity of this species in coastal waters of Southern California. The life cycle experiments showed that processes such as gametogenesis and ecdysis of L. polyedrum are influenced by photon flux density (PFD) and gave a first indication for an involvement of the photosynthetic apparatus in the induction of gametogenesis in dinoflagellates. The light acclimation experiments revealed, for the first time, intraspecific phenotypic diversity in L. polyedrum. The two studied strains differed distinctly in their light requirements and light acclimation ‘strategies’. For the study of intraspecific genetic diversity in L. polyedrum a novel method was developed that allowed the genotyping of individual cells. The application of this novel approach to natural populations showed that population genetic exchange of L. polyedrum in the Southern California Bight is tied to water circulation patterns and that both habitat structure and environmental change leave their signatures in the population genetic composition of L. polyedrum. This thesis represents one of the most comprehensive studies of dinoflagellate population ecology and builds the basis for the development of a holistic concept of the population ecology of L. polyedrum and other dinoflagellate species.

This thesis investigates the role of submarine hydrothermal vents in the global marine Fe budget. While debate continues over the sources of dissolved Fe to the global deep-ocean dissolved Fe budget, it had been presumed, until recently, that all the Fe emitted from hydrothermal vents precipitates and sinks to the seafloor close to the vent source. However, in the open ocean, dissolved Fe exists at concentrations greater than the predicted solubility because of the presence of organically complexed Fe. If similar complexes were formed in the hydrothermal systems then there would be the potential for dissolved Fe export via hydrothermal plumes to the deep-ocean. To investigate the fate of hydrothemally sourced Fe, samples were collected from hightemperature hydrothermal vent-field plumes at 9°N on the East Pacific Rise and at 5°S on the Mid-Atlantic Ridge. The samples from the East Pacific Rise were analysed for Fe and dissolved and particulate organic carbon. Although hydrothermal systems are presumed to be inorganically dominated, elevated concentrations of dissolved organic carbon compared to background seawater were detected in near-field buoyant plumes and the concentration of organic carbon appeared to relate to the total Fe concentration, consistent with the presence of some organic-Fe interaction. Non-buoyant plume samples from the Mid-Atlantic Ridge were analysed for total dissolvable and dissolved Fe and Mn as well as speciation studies on a subset of the dissolved Fe samples using Competitive Ligand Exchange – Cathodic Stripping Voltammetry. The dissolved Fe concentrations in the dispersing plume were higher than predicted from dissolved Fe(II) oxidation rates alone. Further investigation into the speciation of the dissolved Fe revealed the presence of stable Fe-ligand complexes, similar to those detected in the open ocean, but with higher concentrations. If these Fe-ligand complexes were representative of all hydrothermal systems, submarine venting could potentially provide between 11 to 22% of the global deep-ocean dissolved Fe budget. Buoyant plume samples from the same vent site were analysed for total dissolvable and dissolved Fe and Mn as well as particulate Fe, Mn, P, V, Cu, Zn and the rare earth elements. Fe isotopes were also analysed in the particulate fraction, as a potential tool for tracing the biogeochemical cycle of Fe in the ocean. The forms of particulate Fe were elucidated using the particulate trace element data, enabling the isotope fractionation caused by Fe sulfide precipitation to be determined. A diagnostic isotope signature for a potential stabilised dissolved Fe fraction was predicted to be isotopically heavier than the original vent fluid, potentially enabling Fe inputs from hydrothermal vents to be traced throughout the ocean.

Rifted continental margins and extensional basins, provide lasting records of the processes that occur during continental break-up and initial spreading. The eastern Black Sea (EBS) basin provides a good setting to study the development of continental margins, because of ongoing sedimentation during its development and the close proximity of its conjugate margins. Here, I present an analysis of a new wide-angle seismic dataset that reveals the structure of the deep sediments, crust and upper mantle within the EBS basin. These data provide a unique look at the formation of extensional basins, as the dataset includes a prole that is orientated parallel to the rift axis. This prole places new constraints on the variation in magmatism that accompanied continental rifting and the lateral extent over which these variations occur. The wide-angle data show 8-9km of sediment in the centre of the basin, and reveal a wide-spread low-velocity zone (LVZ) within the deep sediments. The depth of this LVZ coincides with the organic-rich mud layer identied as the Maikop, and indicates overpressure within this formation. From the seismic velocity model, excess pore pressures of 60 - 70 MPa above hydrostatic were estimated within the Maikop. The wide-angle data also reveal highly thinned continental crust (7km thick) in the western EBS, and crust interpreted as thick oceanic crust (13km thick) in the eastern EBS, implying a transition from magma-starved to magmatically robust rifting. Lateral variations in mantle temperature and composition can account for a gradual increase in magmatism, but the wide-angle data reveal that this transition is abrupt (30km) and coincides with one of a series of basement scarps. These results impact the interpretations of other rift zones, where a variation in the syn-rift magmatism is observed, but the nature of the transition is not known.