This study investigates d13C and d18O variations in the shells of modern brachiopods that represent all extant groups of calcite-precipitating brachiopods, and were collected live from 8 locations. Protocols and methods of sample preparation are presented that can produce good estimations of annual mean temperatures of ambient seawaters from some brachiopod groups. SEM examinations determined the ultrastructural characteristics of each species prior to isotope analyses. d13C and d18O analyses of shell carbonate were carried out with samples representing different morphological features and ultrastructural shell layers of both ventral and dorsal valves. Generally, d18O values from the fibrous secondary or prismatic tertiary shell layers of the articulated Terebratulida and Rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater. Isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures. d18O values were relatively unaffected by shell specialisation. The only exception was Antarctic species Liothyrella uva, which did not have a complete tertiary shell layer typical of this genus and had d18O values of the innermost layer strongly correlated with d13C and mostly not in oxygen isotopic equilibrium with ambient seawater. With the exception of the rhynchonellid Notosaria nigricans, the outer primary layer material was depleted in d13C and d18C and highly variable. Inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature, therefore only fossil secondary layer material should be used. The anomalous articulated thecideidine brachiopod Thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium.

Numerical simulations of buoyant, gravity-driven coastal plumes are summarized and compared to the inviscid geostrophic theory of Thomas & Linden (2007) and to laboratory studies for plumes owing along a vertical-wall coastline (those of Thomas & Linden (2007) and additional experiments performed at Warwick University). In addition, results of two new laboratory studies with different scales for plumes owing along a more realistic inclined-wall coastline are presented and compared to an extended theoretical model from the geostrophic theory of Thomas & Linden (2007). The theoretical and experimental results for plumes flowing along inclined-wall coastlines are compared to the inclined-wall experimental studies of Avicola & Huq (2002), Whitehead & Chapman (1986) and Lentz & Helfrich (2002), to the inclined-wall scaling theory of Lentz & Helfrich (2002), and to oceanic observations. The lengths, widths and velocities of the buoyant gravity currents are studied. Agreement between the laboratory and numerical experiments, and the geostrophic theories for both vertical-wall and inclined-wall studies is found to depend mainly on one non-dimensional parameter which characterizes the strength of horizontal viscous forces (the horizontal Ekman number). The best agreement between the experiments and the geostrophic theories is found for plumes with low viscous forces. At large values of the horizontal Ekman number, laboratory and numerical experiments depart more significantly from theory (e.g., in the plume propagation velocity). At very low values of the horizontal Ekman number (obtained in the large-scale inclined-wall experimental study only), departures between experiments and theory are observed as well. Agreement between experiments and theory is also found to depend on the steepness of the plumes isopycnal interface for the vertical-wall study, and on the ratio between the isopycnal and coastline slopes for the inclined-wall study.

Changes in mean sea (MSL) level recorded relative to tide gauge benchmarks (TGBM) are corrupted by vertical land movements. Accurate estimates of changes in absolute sea level, require these MSL records to be corrected for ground level changes at tide gauge sites. For more than a decade, the Global Positioning System (GPS) has been used to determine positions of TGBMs and to monitor their position changes, i.e. station velocities, over time in the International Terrestrial Reference System (ITRS). This was initially carried out by episodic GPS campaigns and later on by continuous GPS (CGPS) or a combination of both. Highly accurate realizations of the ITRS, satellite orbits and models for the mitigation of systematic effects currently enable the determination of station positions using GPS at the centimetre or even millimetre level. It is however argued that accurate long--term estimates of changes in the vertical component at the 1mm/yr level cannot be achieved, making intercomparisons between GPS estimates and other techniques necessary. Daily processing and analysis of continuous GPS networks requires automated procedures. The modifications and improvements to the existing procedures at the IESSG are described. The newly developed tools include the monitoring and quality control of daily archived GPS observations and of processing results. A special focus is on the coordinate time series analysis and methodologies used to obtain the best possible estimates of vertical station velocities and associated uncertainties. The coordinate time series of 21 CGPS stations in the UK and France are analysed. Eight of these stations are co-located with tide gauges. The effects of two processing strategies and two realizations of the ITRS on the coordinate time series are investigated. Filtered coordinate time series are obtained by application of a regional filtering technique. Station velocity estimates are obtained by fitting a model including a linear and annual term, and offsets to the unfiltered and filtered coordinate time series. Realistic uncertainties for these velocities are obtained from the application of two empirical methods which account for coloured noise in the coordinate time series. Results from these are compared to the Maximum Likelihood Estimation (MLE), which allows for more rigorous and accurate, simultaneous estimation of the model parameters and their uncertainties. Strategies for coordinate time series analysis on a daily or monthly, and annual or bi-annual basis are defined. At two CGPS stations the dual-CGPS station concept is tested and compared to the single baseline analysis and the application of an adaptive filter. An empirical method to obtain coordinate time series specific filter parameters is described. This investigation shows that reliable relative vertical station velocity estimates can be obtained after much shorter observation spans than absolute vertical station velocity estimates. The availability of dual-CGPS station pairs allows a simplified processing strategy and a multitude of coordinate time series analysis methods, all contributing to a better understanding of the variations in the positions of CGPS stations. Vertical station velocity estimates for the unfiltered and filtered coordinate time series and different analysis strategies are compared for 17 of the CGPS stations and show disagreements of up to 2mm/yr. At the eight CGPS stations co-located with or close to tide gauges alternative estimates of vertical land/crustal movements from absolute gravimetry, geological information and glacial isostatic adjustment models are compared to the GPS estimates, and it is suggested that the latter are systematically offset. An alignment procedure is demonstrated, correcting the vertical station velocity estimates of all 17 CGPS stations for this offset. The correlation of the geology-aligned vertical station velocity estimates and the MSL records from eight tide gauges suggests changes in absolute sea level of approximately +1mm/yr around the UK.

The problem of cross-shore beach face evolution in the swash zone is examined within the framework of the shallow water theory. A system comprising the shallow water and Exner equations is solved numerically using both uncoupled and fully coupled approaches. The uncoupled model assumes that changes in bed height have a negligible effect on the flow over a swash event, whereas the fully coupled model updates the hydrodynamic variables and beach profile simultaneously. In order to obtain accurate results over a single swash event several new numerical solvers based on the method of characteristics (MaC) and the MacCormack (1969) explicit finite-difference scheme are detailed. Particular attention is given to the treatment of discontinuities. A procedure for the explicit treatment of discontinuities, derived from techniques employed in gas dynamical problems, is developed and applied. Certain rather novel shock capturing approaches are also investigated. The shoreline boundary is discussed and a new robust algorithm for the treatment of this boundary on both fixed and mobile beds is presented. The resulting numerical models are used to simulate a variety of different swash events on an initially plane sloping mobile beach. Predictions of beach face evolution are made using the fully coupled approach and are compared with predictions made using an uncoupled analytical beach evolution model based on that of Pritchard and Hogg (2005). The fully coupled model leads to some interesting observations, in particular the possibility of local onshore sediment transport and the occurrence of a seaward facing sediment bore in the backwash. A characteristics based analysis is performed and reveals important differences in the flow structure of coupled and uncoupled swash events. The maximum wave run-up is also considered and it is shown that for the fully coupled system the run-up is significantly less than that predicted by the Shen and Meyer (1963) theory and motion of the leading edge can no longer be determined using simple ballistics concepts. Additionally, for verification purposes, new quasi-analytical solutions are constructed for the mobile bed dam-break problem using two distinct sediment transport formulae.

Since the early Cenozoic, the Earth’s climate has been gradually cooling. Large ice sheets have expanded on several occasions in the past 5000 kyr (50 Ma), with the last major expansion being the onset of major ice sheets in the Northern Hemisphere between 3600 and 2500 ka. This period was characterised by a prolonged increase in ice volume, modulated by orbital forcing. At the same time, major tectonic changes were taking place, with the closure of the Central American Seaway most significant. This thesis aims to address the issue of what caused the onset of major Northern Hemisphere glaciation through an in depth study of samples from North Atlantic ODP Site 982 (57° 31’ N, 15° 51’ W; 1145 m water depth). Multi-species benthic foraminifera composite trace metal records (Mg/Ca, B/Ca, Li/Ca, Cd/Ca) were produced, and the composite Mg/Ca record was used to develop a new regional temperature calibration for the Pliocene. Paleoceanographic records of bottom water temperature and saturation state were produced, as well as bottom water flow speed records using the Sortable Silt (SS) proxy. Bottom water temperature (BWT) records showed an abrupt, ~2°C cooling at 2800-2700 ka, consistent with other previously published records. These data are combined with previously published benthic stable isotope (δ18Ob) records to reconstruct seawater oxygen isotope reconstructions (δ18Osw) across the period of study, and this is found to predominately reflect changes in global ice volume. A major and prolonged increase in ice volume (3500-3000 ka) is identified, equivalent to up to ~55m sea level decrease. The response of the North Atlantic region to this ice sheet growth was tested using previously published sea surface temperature (SST) and δ18Ob records from ODP Site 982, in addition to the new record from this study. The ice volume was found to have influenced the response of SST, δ18Ob, and SS to orbital forcing from changing insolation. Prior to the ice sheet growth, bottom water flow speed varied proportionally with sea surface temperatures, with increased deep water formation during periods of high seasonality. The growing ice sheets responded more slowly to insolation changes, and the presence of this ice sheet increased deep water formation by further cooling saline surface waters. This resulted in feedback loops that intensified deep water flow, leading to a significant increase in North Atlantic Deep water penetration to the southern ocean. A major decrease in δ18Osw at 2800-2700 ka was interpreted as either a loss of Antarctic ice mass, or a reorganization of North Atlantic water masses. Comparison of ice volume records with orbital spectra and reconstructions of the closure of the Central American Seaway suggest the immediate cause of Northern Hemisphere glaciation was a period of orbital conditions favourable to ice sheet growth. Another underlying cause was a series of tectonic shifts, including the closure of the Central American Seaway from 4200 ka, which changed heat and moisture transport patterns to the high latitudes.

This thesis presents a series of numerical modelling studies into hydrodynamic transport and larval dispersal. The initial investigation seeks to evaluate retention timescales in Liverpool Bay. The flushing time and residence time are equal to 136 days and 103 days respectively, however small concentrations of seawater are retained over several years due to vigorous tidal mixing. The age distribution is shown to be highly variable and dependent upon tracer input duration, however salinity can be used to estimate the mean age, which is not directly observable in practice. Chapters 3, 4 and 5 all focus upon the dispersal of meroplanktonic larvae and aim to determine how larval behaviour affects their transport. Vertical migration is a significant influence upon larval dispersal within each case study, although the effect of this behaviour is conditional upon local hydrodynamic conditions. For example diel vertical migration promotes dispersal in the western Irish Sea, however the identical swimming pattern facilitates local retention in the eastern Irish Sea. The ecological implications of these findings are discussed. This thesis concludes with an investigation into the impact of large CO2 leakages on the marine carbonate system at potential carbon sequestration sites in the North Sea. Perturbations to seawater pH are found to vary according to the rate, duration and location of CO2 input. The northern North Sea is particularly vulnerable to large perturbations ( > 1 pH units) during the summer months, as the strong seasonal thermocline suppresses CO2 outgasing.

Exposures of the lower Waterford Formation, Karoo Basin, South Africa provide rare three-dimensional control to an exhumed low-gradient basin margin, which permits increased understanding of sub-seismic scale process-regime and lateral variability. The study section overlies a 500-m-thick channelized submarine slope succession and is subdivided into eight mappable parasequences clinothems. The central 40 km 2D reference profile parallel to depositional dip (i.e. west-to-east) enables characterization of the shelf-to-slope transition for two successive clinothems and the establishment of robust criteria for identifying the shelf edge at outcrop. The two clinothems exhibit differing process responses to the gradient increase at the shelf edge rollover. The fluvial-dominated, mouth-bar clinothem of WfC 3 exhibits a 5 km dip-parallel zone of extensional growth faulting at the shelf edge with limited delivery of sediment beyond the shelf edge rollover. In contrast, WfC 4 is a wave and storm dominated shoreface-clinothem that supplied a thick upper slope turbidite succession via closely spaced gullies at the shelf edge and a large upper slope channel. This suggests that the delivery of sediment to deep-water settings is governed by parameters other than the presence and proximity of a fluvial point source, which is heavily advocated in current models for shelf construction. It would be common practice to attribute variability between successive clinothems on a single 2D dip profile to lateral variability across the basin margin. However, two additional, sub-parallel dip profiles across depositional strike to the north and south of the reference profile indicate significant 3D variability in the nature of the clinothems. A greater supply of sediment to the upper slope in the north of the region, in the absence of a clear fluvial driver, suggests that the deltaic/shoreface system was able to transit quickly to the shelf edge and establish itself in that position for an extended period. Increasing parasequence thickness toward the north indicates greater accommodation in this area throughout the lower Waterford succession. It is therefore likely that differential subsidence across the margin controlled the position of the shelf edge and maintained a narrower shelf in the north, which would have had significant influence on sediment routing paths, diverting them to the north. Abundant shelf-confined soft sediment deformation in successive clinothems along all three dip margin profiles is attributed to instability on the frontal slopes of inner shelf deltas, due to high rates of sediment supply. The basinward splitting and abrupt thinning of deformed packages beyond the inferred shelf edge rollover shows that the presence of soft-sediment deformation alone is not an adequate criterion with which to define the shelf edge rollover. The significant thickness of shelf deposits without subaerial exposure indicates that the margin was subject to a relatively high subsidence rate but that the rate of sediment supply was sufficient to drive the system to the shelf edge and deliver sand to the slope without the development of incised valleys. Therefore, the lower Waterford Formation is considered a high accommodation / high supply system. This study provides a high-resolution outcrop-based dataset with three-dimensional constraints. It enables greater understanding of the controls on basin margin construction, and the sub-seismic scale processes that control the spatial and temporal variability of sediment delivery to the slope and basin floor.

Landfast sea ice is a recurring seasonal feature along many coastlines in the polar regions. It is characterised by a lack of horizontal motion, for at least 20 days, and its attachment to the coast or seabed. It can form as a result of restrictive geometry, such as channels or embayments, or through the grounding of thick ice ridges which add lateral stability to the ice cover. Due to its stationary and persistent nature, landfast ice fundamentally modifies the exchange of heat and momentum between the atmosphere and ocean, compared with more mobile pack ice. The current generation of sea ice models is not capable of reproducing certain aspects of landfast ice formation and breakup. In this work two landfast ice parameterisations were developed, which describe the formation and breakup of landfast ice through the grounding of thick ice ridges. The parameterisations assume the sub-grid scale distribution of ice draft and ocean depth, the two parameters important in determining the occurrence of grounded ridges. The sub-grid scale distribution of grounded ice is firstly defined by assuming that ice draft and ocean depth are independent. This parameterisation allowed ice of any thickness to occur and ground at any depth. Advancing from this the sub-grid scale distribution of the grounded ice was restricted in an effort to make it more realistic. Based on Arctic ice scour observations ice was prevented from grounding in regions where the draft thickness was much larger than the ocean depth. Both parameterisations were incorporated into a commonly used sea ice model, the Los Alamos Sea Ice Model (CICE), to which a multi-category ocean depth distribution from high resolution global bathymetry data (ETOPO1) was included. The parameterisations were tested in global standalone format (i.e. no active ocean) with realistic atmospheric forcing. Both parameterisations were found to improve the spatial distribution and the seasonal cycle of landfast ice compared to the control (i.e. no landfast ice parameterisation) in the Arctic and Antarctic. However, the grounded ridges produced by the parameterisations were very stable, and tended to become multiyear leading to the production of multiyear landfast ice, which was particularly widespread in the Antarctic. It was found that tides have a significant impact on both grounded and landfast ice. In some polar locations tides were found to increase the occurrence of landfast ice, by increasing the production of thick ridges which were able to ground. Conversely, in some regions, tides were found to decrease the occurrence of landfast ice, as strong tidal and residual currents increased the mobility of the grounded ridges and landfast ice. This thesis finishes by considering whether a sea ice model could be used to further our understanding of the physical landfast ice system. Analytically derived characteristic numbers, which describe the ability of landfast ice to form, were found to fully describe the formation of landfast ice within the sea ice model CICE during idealised 1D scenarios. For these scenarios the key parameters controlling ice motion were found to be the external forcing component, the width of the ice cover, the internal ice strength, and the thickness of the ice. However, an exact characteristic variable able to describe the occurrence of landfast ice in an idealised 2D scenario could not be found analytically, nor could it be inferred numerically, and this remains an area for further research. This thesis examines different methods of modelling landfast sea ice and provides the sea ice modelling community with a means to parametrise landfast ice formation as a result of grounded ridges without having to work at very fine resolution, as this is computationally inefficient.

Shelf seas are believed to play an important role in the oceanic export of carbon (C). The combination of enhanced primary productivity partly induced by highly energetic mixing, together with the euphotic zone being in close proximity to the seabed, make the shelf seas highly efficient region for biological C sequestration. The high productivity observed in shelf seas also has high economical significance by supporting >90% of the global fish catch. A subsurface peak in biomass, termed the subsurface chlorophyll maximum(SCM), at the base of the thermocline occurs as a result of phytoplankton being nitrate limited in the surface layer. The SCM is believed to be responsible for as much primary production as the spring bloom. The turbulent supply of nutrients across the thermocline, driven by the internal tide and wind-driven inertial oscillations, is believed to support growth at the SCM. However, although inertial oscillations are recognised as an important mixing mechanism, the turbulent flux of nitrate that they supply has not yet been estimated. In this thesis the importance of diapycnal fluxes of nutrients, particularly those generated by wind-driven inertial oscillations, is investigated in terms of sustaining productivity in the SCM, using a Lagrangian numerical model, observational and experimental approaches. The results in this study indicate that diapycnal nitrate fluxes limit new production at the SCM, and mixing generated by wind-driven inertial oscillations play a key role in supporting primary production at the SCM. In addition, this study demonstrates that the background nitrate flux, as well as transport of nitrate via dinoflagellate migration, are too low to sustain primary productivity at the SCM. Our observations demonstrate that wind-driven large, short-lived dissipation events increase the daily nitrate flux to the SCM by a factor of at least 17, supplying the SCM with ~33% to 71% of the nitrate required fornew production in shelf seas during summer. Thus it is intermittent mixing events which must supply the required nitrate for new production at the SCM. Using an experimental approach, a wind event was simulated in order to estimate the impact of mixing of water from the SCM and BML on primary and secondary production in the SCM. Nutrients were assimilated rapidly and phytoplankton production increased as expected. However, up to two thirds of the C fixed was exuded as DOC and there was a significant increase in bacterial activity. As well as supplying nutrients to the SCM, we show that diapycnal mixing may also be important in redistribution plankton, especially bacteria, which subsequently impacts both the inorganic and organic nutrient pools. Thus the sensitivity of the SCM, in terms of autotrophy and heterotrophy, to diapycnal mixing is highlighted. This study highlights the importance of short-lived events in supplying nutrients to the SCM. Concluding that these are likely undersampled and also not well represented in shelf sea models. In addition, this thesis demonstrates that there is a need to consider secondary as well as primary production to fully understand the C cycle in the shelf sea.

Marine primary productivity by phytoplankton drives the conversion of CO2 into organic carbon, thus supporting key marine ecosystem services such as biogeochemical nutrient cycles and fisheries. Therefore, the ability to accurately quantify and predict the environmental influences that govern this process is of paramount importance. Through surveying and experimental approaches, I investigated the variability of phytoplankton physiology and biomass across a range of light and nutrient environments. I found that growth and physiological responses differ in geographically distinct regimes of nutrient limitation across the North Sea. Variable nutrient stoichiometry across the region could therefore lead to alternative growth and productivity rates that reflect the populations suited to the different conditions. Fast repetition rate fluorometry (FRRf) measurements of photosystem II (PSII) characteristics during a spring bloom were shown to change with hydrography and community composition. Thus, providing further support that the physiological state of PSII can be used as an indicator of bloom status and community composition. FRRf-derived productivity parameters were also measured and shown to change in response to changes in taxonomy. Through geostatistical approaches the spatial distribution of phytoplankton was characterised during a spring bloom. I show both in situ and satellite sampling approaches possess the ability to capture mesoscale variability in phytoplankton distribution, but ocean colour estimates lose accuracy in highly heterogenous conditions. This thesis provides a step towards capturing the extent of spatial and temporal variability in phytoplankton stocks and rates in temperate shelf seas, in part, by providing a better understanding of the strengths and limitations of the use of fluorescence-based measurements.