The use of coccolithophores has until recently been restricted mainly to biostratigraphic indicators. Their small size makes it difficult to obtain species-specific geochemical data and they are often perceived to preserve poorly compared with the larger foraminifer. In the last decade the study of potential coccolithophore bio-geochemical proxies has taken off, but with little to support their use in deep-time records. The suitability of fossil coccolithophores for geochemical proxies has been examined. A large collection of trace metal data from individual coccoliths throughout the Cenozoic has been collected, from a range of taxa. Using SIMS it has been demonstrated that the Sr/Ca values from fossil coccoliths are comparable to those collected from their modern counterparts. It has also been possible to examine the distribution of ions within individual coccoliths, revealing that their original calcite is preserved and the effects of diagenesis can often be overcome. For the first time a high-resolution record of Sr/Ca from calcareous nannofossils has been produced over the Eocene/Oligocene transition, (~34 to 33.5 Ma). This period of extreme climate change resulted in the permanent formation of ice, for the first time in the Cenozoic, at the Antarctic within ~400 ky, accompanied by a general shift to a modern climate state. This shift is associated with changes in nutrient cycling and/or ocean thermal structure due to changes in ocean circulation. It is still debated about how these changes affected productivity in the equatorial Pacific at this time. The Sr/Ca proxy provides a direct record of coccolithophore productivity. Using samples from IODP Site U1334, bulk and individual coccolithophore carbonate are examined, in combination with the coccolithophore isotopic record. The factors affecting the records are examined in detail and reveal a significant shift in productivity over the E/OT, associated with isotopic changes.

Estuaries are the transition between freshwater and marine environments, and regulate the delivery of riverine fluxes to the oceans. The Humber estuary (UK) is considered a major source of nutrients to the North Sea. It is a highly turbid and dynamic macrotidal estuary that receives contaminated fluxes from agriculture, urbanisation, industry and historical mining activities. The chemistry of the river water and the sediments is modified within the estuarine continuum due to mixing. Sediments are subjected to resuspension periodically (on a tidal cycle timescale) and occasionally or seasonally (due to extreme rainfall or flooding episodes), which triggers a series of redox processes that control nutrient and pollutant cycling. During simulated sediment resuspension in aerated conditions, the release of accumulated reduced substrates (ammonium, manganese, iron, sulphur) and trace metals were reversed within relatively short timescales, which is important when assessing the environmental consequences of different resuspension episodes. However, the position in the salinity gradient was the dominant control on sediment geochemistry since a transition from the inner estuary (Mn/Fe-dominated redox chemistry) to the outer estuary (Fe/S-dominated redox chemistry) was observed. To better understand the role of the benthic biogeochemical denitrification processes in the nitrogen cycling, nitrate-dependent oxidation was also investigated in microcosm experiments. The same transition was observed in the nitrate reduction coupled with the oxidation of different inorganic species from the inner to the outer estuary. In this oxidation scenario there was also evidence of trace metal mobilisation. Due to the greater availability of electron donors in the mudflats of the outer estuary, they showed the greatest potential for denitrification and therefore are considered a relevant nitrogen sink in the Humber estuary. Furthermore, in this context of highly spatiotemporal variability, benthic microbial diversity showed a decreasing trend with increasing salinity, but sediment mixing and transport and the presence of strong redox transitions were also environmental parameters shaping the microbial communities in the Humber sediments.

Marine organisms are exposed to a range of environmental stressors, including anthropogenic pollutants and ocean acidification, which may have harmful effects. The reproductive processes of broadcast spawning marine invertebrates are considered to be particularly vulnerable to environmental insults. Predicting the potential impacts of ocean pollution and acidification on reproductive success is essential to anticipate the consequences of predicted marine change. This study evaluated the effects of exposure to the pharmaceutics diclofenac, ibuprofen and sildenafil citrate (Viagra), the metals cadmium and copper, and the endocrine disrupting compound nonylphenol (singly and under simulated ocean acidification scenarios; pH 8.1, 7.9 and 7.7) on sperm motility and fertilisation success of Asterias rubens, Psammechinus miliaris and Arenicola marina. Sperm motility was determined by Computer Assisted Sperm Analysis (CASA) and fertilisation success by the presence of embryonic cleavage at 60 minutes after fertilisation. Sperm motility (percentage of motile sperm and swimming speed) was reduced by nonylphenol concentrations ≥0.1μg/l, diclofenac ≥ 1.0μg/l, cadmium 1000μg/l, copper ≥10μg/l and ocean acidification of pH 7.9 and 7.7. Exposure to ≥ 1.0μg/l of ibuprofen only affected P. miliaris sperm. Exposure of sperm of A. rubens and P. miliaris to sildenafil citrate at concentrations ≥ 18ng/l and ≥ 50ng/l respectively increased both percentage motility and swimming velocity. Sperm pre-incubated in test conditions prior to fertilisation showed significant reductions in fertilisation success in all single pollutant and ocean acidification scenarios with the exception of ibuprofen for which only P. miliaris was negatively affected. Pre-incubation with sildenafil citrate significantly increased fertilisation success of A. rubens and P. miliaris but not for A. marina. Curiously, the pre-incubated oocytes of P. miliaris, A. rubens and A. marina appeared remarkably robust to some of the pollutants at ambient pH. However, fertilisation was significantly inhibited when exposed to diclofenac, copper, cadmium and seawater pH 7.9 and 7.7 as single stressors. Fertilisation success of P. miliaris and A. marina was adversely affected by sperm-oocyte incubation of ≥20 minutes with 100μg/l and 100μg/l of ibuprofen respectively. Combined nonylphenol and elevated seawater pH significantly reduced sperm motility and fertilisation success. These results demonstrate the potential for marine invertebrates to be affected by single pollutants and suggest that these effects may be more severe under predicted ocean acidification conditions.

This thesis consists of three parts with the unifying theme of applying emulators and other statistical methods to the investigation of sensitivities and uncertainties in tsunami models. The first part contains the statistical emulation of the wave time series at fixed locations that are obtained using an analytical landslide-generated tsunami computer model. Leave-one-out diagnostics are used to validate the emulator, showing excellent agreement in predictions and model evaluations. The emulator is used for sensitivity and uncertainty analyses, where many evaluations are necessary. The computational time required for both analyses is at least 20,000 times lower using the emulator instead of the computationally expensive model. The second part investigates the significance of the seabed deformation representation on tsunami wave predictions of the advanced VOLNA tsunami model. A novel realistic representation of the tsunami source deformation using quadratic curves is compared with simpler representations used in existing tsunami models: single block, four blocks, sixteen blocks and “piano keys”. Factor-of-two differences in wave elevations obtained for different representations of seabed deformation. The last part presents an investigation of tsunamis produced by different fault rupture scenarios on the Cascadia Subduction Zone. Polygons are used to model the source geometry and quadratic curves the deformation in different source event scenarios that are chosen using experimental design. The VOLNA model is evaluated for these scenarios to explore how the source characteristics affect the wave amplitude and coastal inundation predictions. Statistical emulation is applied to a large number of locations in order to investigate the use of emulators in place of expensive tsunami simulators in practical applications. The leave-one-out diagnostics show that the application of Registration and Functional Principal Components techniques to the emulation process leads to improved predictions. Finally, a limiting event is investigated in order to obtain the worst-case scenario inundation along the whole margin in a single simulation.

This thesis is motivated by recent field observations of tsunamis which point out that use of solitary waves as model tsunami is not theoretically justified. In order to generate very long waves in laboratory, a bottom-tilting wave maker is designed and used at the University of Dundee. This new type of wave maker can produce waves longer than the effective length of solitary waves, which provides better long wave model. The main idea of the bottom-tilting wave maker is that moving the entire bottom can lead to the wave as long as the given wave tank. Meanwhile, some analytical solutions and numerical models are developed in this research for theoretical investigation. Wave behaviour in the tank without beach and the wave run-up on a plane beach are of main interest. The unique contributions for the two scenarios are that wave profile or run-up height of very long waves with a variety of bottom motions and surface problems have been investigated, respectively. A series of experiments are conducted in the new wave tank by inputting the prescribed bottom motions to the electrical motor with varying water depth, bottom motion displacement and speed. The free surface elevation time-histories are measured by acoustic wave gauges while the maximum run-up heights of varying waves are observed by a video camera. Nonlinear and dispersive numerical models are developed in this thesis for modelling the wave tank. A shock-capturing finite volume scheme with high-order reconstruction method is used to solve the governing equations, coupling with a computational domain mapping technique to estimate the moving shoreline. By comparing to the experimental measurements, the numerical models are verified and able to approximate the resulting waves in the wave tank. Surface waves studied in Boussinesq scaling with time-dependent bottom bathymetry gives a better performance in approximating the wave generation in the tank without a beach, while nonlinear shallow water system is good at approximating the wave run-up on a plane beach. The computational domain is as long as the wave tank and bounded by two fully-reflective vertical walls at the two ends. The analytical solutions of the time-history of free surface elevation are derived by the linear wave theory in an infinite domain. To further extend the study, the numerical model based on the Boussinesq equations in a semi-infinite wave tank is developed, in order to estimate the wave period which can not be easily determined from the experiments and to explore the wave profile in a tank with long propagation distance. For wave generation in the tank without a beach, it can be verified that the new wave maker can provide new long wave model better than solitary waves by the theoretical results from the linear wave theory and the numerical model based on the Boussinesq equations. All the waves within the measured range are longer than the effective wavelength of the solitary waves with same wave amplitude, which can reach seven times longer at most. Using both the theoretical and experimental results, the relations between the bottom motions and the resulting waves have been investigated in terms of the wave amplitude, wave peak time and wave period. Note that only for estimating the wave period is assumed that the wave tank has semi-infinite domain by using the Boussinesq equations. In particular, wave amplitudes can be expressed by power function. For wave run-up on a plane beach, the parametric studies based on the nonlinear shallow water equations reveal how the run-up height relates to the bottom motion and the leading wave profile in a wave tank with adjustable beach slope. Monotonous dependence of the maximum run-up height on the wave height or wave-front steepness is discovered. Furthermore, the influence of the bottom friction and wave breaking are addressed.

The Southern Ocean is governed by strong wind forcing, energetic eddies and probably intense internal wave fields, which are considered to be generated in part by interaction of the eddy field with bottom topography. While wind and eddy forcing have been recognized in the dynamical balance of the Southern Ocean Meridional Overturning Circulation (MOC), the role of internal waves remains uncertain. The present study aims to investigate the extent to which the interaction of an energetic eddy field with realistic bottom topography, leading to diabatic forcing of the interior stratification through internal wave breaking, can sustain a deep overturning circulation and provide an additional leading order term in the Southern Ocean MOC that is unaccounted for by current theories and numerical models. A hierarchy of experiments to test this hypothesis is conducted in this thesis. The MIT General Circulation Model (MITgcm) is configured to simulate a circumpolar current in two individual versions of a zonal channel, namely a coarse-resolution setup with Gent-McWilliams eddy parameterisation and a mesoscale eddy-resolving setup. The energy input that arises from internal wave breaking and forces the buoyancy budget of the MOC is parameterised in the model via a vertical diffusivity profile. Initially forced to follow a simple constant shape, this diffusivity profile is subsequently estimated online via the internal lee wave energy generation rate, which is calculated from the model stratification, velocities and from prescribed sub-grid-scale topography, following nonlinear internal lee wave theory. Results from the individual experiments are discussed in view of the extent and mechanisms by which internal waves generated by eddy-topography interaction force the cross-channel MOC. The main results of this thesis show that the internal lee wave energy generation rate enhances the diapycnal diffusivity near the bottom, which results in a substantial increase in the strength of the residual MOC of the lower limb and a warming of the deep interior of the channel.

This study investigates the basin-wide oceanic variability associated with the Madden-Julian Oscillation (MJO) using new observations from the global array of profiling floats, known as Argo. Analysis of the Argo gridded data in a case study of the December 2003 to February 2004 MJO event in the Pacific Ocean reveals that the oceanic variability along the equator is characterised by an eastward propagating Kelvin wave response to the MJO surface wind stress anomalies. The observed phase speed and latitudinal structure are characteristics of the first baroclinic mode Kelvin wave. The vertical structures of these Kelvin waves are observed for the first time to extend downward to 1500 m. The amplitude of the deep ocean temperature anomalies is up to three times the amplitude ofthe observed annual cycle. With unprecedented coverage of salinity observations in the deep ocean provided by the Argo data, systematic changes in subsurface salinity variability during the MJO event are revealed for the first time. It is found that the salinity changes are associated with the Kelvin wave displacing isopycnals vertically. The composite study for the full period of the data set from January 2003 to December 2006 confirms the dominance of the Kelvin wave response in the subsurface temperature and salinity variability in the Pacific Ocean. Composites of sea surface temperature and sea surface salinity anomalies suggest the role of horizontal advection mediated by the Kelvin waves in addition to the MJO associated surface heat and fresh water fluxes variation. In the Indian Ocean, there is some evidence of a dynamical response to surface wind stress changes in the form of local upwelling and downwelling along 0°_5° Sin the central basin as well as in the equatorial eastern basin. However, the response did not exhibit propagating characteristics similar to the Pacific Ocean counterpart.

No description available.

Climate change exists as a significant threat to the future well-being of the planet. There is reason to suggest that among the potential abrupt climate changes that may occur, the possibility of a collapse of the thermohaline circulation (THC), popularly referred to as the Gulf Stream, has often been the focus of media and political attention and discussion in the UK. This is despite the risk of such a collapse being poorly understood and quantified. This thesis draws on perspectives from the fields of media studies, sociology, and science and technology studies and draws on a mixed-methodology approach to investigate how and why the possibility of a THC collapse has emerged as a public risk issue in the UK and with what potential consequences. The thesis is particularly interested in how representations of the possibility of a THC collapse have emerged and developed over time and how they illustrate the struggle between different actors and fields of society (scientific communities, the media system, political institutions, corporations and campaigning groups and social movements) to advance particular courses of action. The findings from this research indicate that the THC issue has been popularised in the media largely because of the high-consequence, UK-focused and paradoxical nature of the risk. The thesis shows that the THC issue has been used by actors from many different disciplines, and represented in a variety of ways, to advance a contrasting range of treatment recommendations. Treatment recommendations range from urgent action to reduce carbon emissions to no action at all. It is shown that uncertainty in the science of the THC has been essential in allowing the possibility of a collapse to be used to advance such a range of treatment recommendations because it has afforded actors a significant amount of flexibility in their representations. Contextual factors that have influenced media coverage and the nature of representations are discussed. Evidence is put forward which suggests that the emergence and popularisation of the THC issue may have had effects upon public, political and organisational perceptions of (abrupt) climate change, trust in science, investment in scientific research, and effects upon political action to address climate change. The thesis uses the Field of Mediated Risk Communication model to conceptualise the way in which representations of particular risk issues are communicated and contested between different fields of society. The findings from the analysis of the emergence and development of the THC issue are used to put forward a revised version of the model.

Levels of atmospheric oxygen (02 ) hav(' increaseo from <2o/r:. of the present atlnospheric level (PAL) to values similar to the PAL during the N('oproterozoic. This is likely to have resulteo in significant changes in redox conditions in thp ocpans. The aim of this stud.v is to provide new constraints on redox conditions in shallow seawater during the Neoproterozoic by analysis of the rare earth element (REE) concentration and chromium (Cr) isotopic composition of marine carbonatps. To this end, a new method for J 53Cr analysis in low concentration samples has been developed. In addition, the Cr isotopic composition of modern and Phanerozoic carbonates, and seawater, have been determined to provide new constraints of the environmental behaviour of Cr isotopes. Modern seawater is characterised by heavy J53Cr values (+0.55-1.55%0) relative to the continental crust (-0.12%0), which indicates that Cr isotopes are fractionated during oxidative weathering. Importantly, the Cr isotopic composition of modern carbonates, precipitated in shallow water, is within the range of seawater. This suggests that fractionation of Cr isotopes during carbonate precipitation is minimal, and carbonates should provide a record of seawater J53Cr. Carbonate samples of Phanerozoic age also have high J 53Cr values (0.737-1.994%0), consistent with oxidative weathering on the continents at this time. Most of the Neoproterozoic carbonates have significantly lower J53Cr values than the modern and Phanerozoic carbonates. However, oolitic limestones deposited just prior to the first Cryogenian glaciations, have higher J53Cr (+0.571-1.004%0). Together, the J 53Cr and REE data suggest that the operation of the Cr cycle was significantly different in the Neoproterozoic. Changes in J53Cr reflect eitlwr a shift in the relative importance of riverine and h~'drothermal sources, and/or changes in levels of atmospheric O2 . Modelling indicates that shallow waters were either dysoxic or suboxic during the Cryogenian, ano levels of atmospheric O2 must have been less than 30-40% PAL.