Submarine slides can generate tsunami waves that cause significant damage and loss of life. Numerical modelling of submarine slide generated waves is complex and computationally challenging, but is useful to understand the nature of the waves that are generated, and identify the important factors in determining wave characteristics which in turn are used in risk assessments. In this work, the open-source, finite-element, unstructured mesh fluid dynamics framework Fluidity is used to simulate submarine slide tsunami using a number of different numerical approaches. First, three alternative approaches for simulating submarine slide acceleration, deformation and wave generation with full coupling between the slide and water in two dimensions are compared. Each approach is verified against benchmarks from experimental and other numerical studies, at different scales, for deformable submarine slides. There is good agreement to both laboratory results and other numerical models, both with a fixed mesh and a dynamically adaptive mesh, tracking important features of the slide geometry as the simulation progresses. Second, Fluidity is also used in a single-layer Bousinesq approximation in conjunction with a prescribed velocity boundary condition to model the propagation of slide tsunami in two and three dimensions. A new, efficient approach for submarine slide tsunami that accounts for slide dynamics and deformation is developed by imposing slide dynamics, derived from multi-material simulations. Two submarine slides are simulated in the Atlantic Ocean, and these generate waves up to 10 m high at the coast of the British Isles. Results indicate the largest waves are generated in the direction of slide motion. The lowest waves are generated perpendicular to the slide motion. The slide velocity and acceleration are the most important factors in determining wave height. Slides that deform generate higher waves than rigid slides, although this effect is of secondary importance for generated wave amplitudes.

The OSMOSIS project used a fleet of gliders to survey at the Porcupine Abyssal Plain (North Atlantic) from September 2012 to September 2013. Different physical and biogeochemical parameters (salinity, temperature, oxygen concentration, chlorophyll fluorescence) were measured in the top 1000 m of the water column. The present study focused on calibrating and analysing the oxygen concentration data. The mixing layer depth was defined as the depth where oxygen concentration varied by more than 0.5% from its value at 5 m. The mixing layer was shallower than the mixed layer, defined by density and temperature. In cases of low turbulence, the mixing layer described the vertical extent of the biologically productive layer (except deep chlorophyll maximums). Net community production was calculated over a year-cycle with an oxygen-budget approach. Net autotrophy was found at the site with a net production of (6.4 ± 1.9) mol m-2 in oxygen equivalents. The period exhibiting a deep chlorophyll maximum contributed (1.5 ± 0.5) mol m-2 to the total production. The results were higher than most of the previous estimates and the productive season longer than that considered in previous studies. Increased net community production was related to the decrease in water turbulence and mixing layer shoaling, confirming the validity of the mechanism proposed by the model of Enriquez and Taylor (2015). Gross primary production was calculated from the difference between rate of oxygen increase during the day and decrease during the night, diel cycle shown by in situ data in the top 20 m of the column. Physical processes often disrupted the biological diel cycle and restricted the analysis to four periods during the year. The gross primary production ranged between 6 mmol m-2 d-1 and 13 mmol m-2 d-1. Results suggest an enhancement of the gross primary production when the mixing layer shoals.

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The stratospheric winter polar vortex consists of strong westerly winds; this winter flow regime can undergo a complete breakdown during sudden stratospheric warming events. In the Northern Hemisphere these events are often accompanied by the descent of anomalous flow regimes which can result in extreme surface weather. The focus of this thesis is to assess sudden stratospheric warmings and their place in the coupled climate system. Portions of this work are dedicated to algorithm development with the aim of quickly and accurately isolating and subcategorising events. A method is successfully created that is computationally cheap, easy to implement, based on dynamically relevant criteria and has error rates clearly outlined. Impacts on the surface and ocean are assessed with focus on specific subclasses of sudden stratospheric warmings. It is found that there is, on average, stronger surface and oceanic impacts following events that split the polar vortex. The ocean system is impacted via modifications to the implied Ekman heat transport and the net atmosphere-surface heat flux. Furthermore, there is a relationship between the initial location of the disturbed polar vortex and the strength of anomalous flow regime at the surface. Analysis is conducted predominantly using general circulation model output, with direct comparison between an atmosphere-only model and a coupled atmosphere-ocean model. For the coupled model there is a reduction in the number of simulated sudden stratospheric warmings, a result of altered atmospheric wave dynamics. This is partially attributed to a cold bias over the equatorial Pacific. The frequency of sudden stratospheric warmings is found to be insensitive to North Atlantic sea surface temperature anomalies.

This thesis investigates some important aspects of the atmospheric branch of the hydrological cycle in the modern day climate from an observational perspective. Data quality is evaluated, focusing on two state-of-the-art reanalysis products, ERA-I and JRA-55. Regional-scale discrepancies among reanalyses and observations, especially in their annual cycles, are found in the warm pool, Amazon, Gulf stream and Indian subcontinent regions. In the tropics, oceanic evaporation and its temporal variability are notably greater in JRA-55 than in ERA-I and satellite-based estimates, while both reanalyses overestimate precipitation. Higher tropical precipitation and evaporation, accompanied by a slightly lower level of total column water (TCW), might suggest a more intense hydrological cycle, but this can be an ill-defined concept especially when analysis increments mask “spin-down” errors in reanalysis models. Analysis increments arise to remove unphysical residuals in the atmospheric water budget, and these are explored via a cluster analysis to identify regimes with common behavior. Consistent for ERA-I and JRA-55, the regime with the largest negative residuals (greater moisture outputs than inputs) exceeding 50% of mean precipitation occurs during the dry season of some low latitude regions that feature strong seasonality, high evapotranspiration and high moisture divergence. Errors in the moisture divergence are likely responsible because they correlate strongly with the budget residual. Empirical Orthogonal Function (EOF) and Self Organizing Map (SOM) analyses are applied to identify the dominant inter-annual patterns of vertically-integrated moisture divergence variability. They reveal that the transition from strong La Niña through to extreme El Niño events is not a linear one and that the EOF orthogonality constraint results in the patterns being split between leading EOFs that are non-linearly related. The SOM analysis captures the range of responses to the El Niño Southern Oscillation (ENSO), indicating that the distinction between the moderate and extreme El Niños can be as great as the difference between La Niña and moderate El Niños, from a moisture divergence point of view. On diurnal time scales, horizontal moisture fluxes vary in response to thermodynamic and dynamic effects. TCW shows a global scale diurnal cycle that peaks around 1800 - 2100 local time with a peak-to-trough magnitude of 0.4mm. Semi-diurnal variations in surface winds and pressure, consistent with atmospheric tidal theory, create a westward propagating moisture convergence/divergence wave along the equator. Finally, the importance of Tropical Cyclones (TCs) as a source of freshwater for the North American continent is estimated using an ensemble of schemes designed to attribute onshore moisture fluxes to TCs. Averaged over the 2004–2012 hurricane seasons and integrated over the western, southern and eastern coasts of North America, the seven schemes attribute 7 to 18% (mean 14 %) of total net onshore flux to Atlantic TCs. A reduced contribution of 10% (range 9 to 11 %) was found for the 1980–2003 period, though only two schemes could be applied to this earlier period. Over the whole 1980–2012 period, a further 8% (range 6 to 9% from two schemes) was attributed to East Pacific TCs, resulting in a total TC contribution of 19% (range 17 to 22 %) to the ocean-to-land moisture transport onto the North American continent between May and November. The inter-annual variability does not appear to be strongly related to ENSO.

Halogens have an established impact on atmospheric composition, but further quantification of their global air-quality and climatic impacts is needed. This thesis documents the development of a simulation to represent the atmospheric chemistry of iodine within a wider halogen framework. Following the development of the iodine simulation (Chap- ter II-III), a coupled model is presented (Chapter IV) that brings together and builds upon previous halogen (Cl,Br) studies in GEOS-Chem. Finally this model is used to investigate impacts of halogens on climate (Chapter V), and iodine sourced aerosol (Chapter VI). Significant implications of halogens on oxidants are shown. Iodine alone reduces the tropospheric O3 burden by ∼9 %, with “coupled” halogens (Cl,Br,I) reducing it by ∼15 %. Global mean OH concentrations decrease by 4.5 % on inclusion of halogens. However, this is due to competing factors. The O3 loss decreases primary production, whereas conversion of HO2 to OH via photolysis of hydrohalic acids tends to increase it. Chlorine provides a potent new oxidant in the model. For some VOCs (C2H6, (CH3)2CO) Cl oxidation provides up to ∼20 % of their sink. The effect of halogens on the tropospheric O3 radiative forcing (RFTO3) is investigated. Halogens cause a feedback effect, dampening the increase of tropospheric O3 between the pre-industrial and the present day by ∼20 %, therefore reducing RFTO3. Aerosol-phase iodine is also investigated and shown to regionally contribute up to 101 % of DMS sourced sulfate aerosol mass. In the pre-industrial, iodine aerosol can regionally contribute up to 21 % of the sulfate mass. Iodine and halogen chemistry in general are required to understand tropospheric composition and processes. Uncertainty in the emissions, chemistry and loss processes for halogens is high. Further in-situ observations and elucidation of key parameters in laboratories are urgently needed to refine our understanding of this important aspect of atmospheric chemistry.

The transition from the Greenhouse Eocene climate (55-34Ma) to the Icehouse regime of the Oligocene (34-23Ma) was marked by a widespread cooling at the Eocene-Oligocene Transition (EOT) (~34Ma), followed by major Antarctic glaciation. The relative contribution of changes in ocean circulation and continental weathering is however not well understood. This thesis takes advantage of new core material recovered during IODP Expedition 318 to Wilkes Land, Antarctica, to study ocean-continent interaction during this critical time interval. To this end, I have used neodymium (Nd) isotopes in fossil fish teeth to reconstruct water mass composition and ocean circulation. Secondly, I have used Nd isotopes in bulk sediments as a provenance tool to reconstruct erosional patterns on the continent. Additionally, I have used a combination of major and trace element data to evaluated the robustness of Nd isotopes in fossil fish teeth as a water mass tracer in a marine shelf environment, and under changing redox conditions at the seafloor. My findings are presented in four distinct chapters and yield the following conclusions: i) fossil fish teeth appear to be robust recorders of authigenic Nd in a shelf setting and remain robust under changing redox conditions within the sediments; ii) a multi-site authigenic Nd isotope study in the Tasman region of the Southern Ocean indicates active deep water formation in the Southern Ocean, and excursions recorded are the result of a previously unreported widespread perturbation to the hydrological cycle on Antarctica; iii) the first authigenic Nd record from the North Atlantic EOT is consistent with a change in deep water masses coinciding with the transition to a cooler climate, and iv) changing sediment provenance indicates a dynamic Antarctic ice sheet throughout the Oligocene.

Described in 1956 as an oceanographic curiosity, salt fingers are now recognized as an important mechanism for vertical transport in fluids that may play a key role in areas so diverse as stellar formation, oceanography and material science and engineering. Complete life cycles of salt fingers will be modeled and analyzed using a combination of finite difference and analytical methods. Some commonly held assumptions about fingering phenomena will be challenged, and some conclusions regarding the origin and maintenance of the finger structure, as well as the dependence of the fingering process on several defining parameters, will also be drawn and discussed.

Understanding the chemical composition of organic-rich marine sediments has the potential to: 1) allow evaluation of variations in ocean chemistry, enabling assessment of changes in global processes throughout geological time; and 2) provide an increased temporal and spatial understanding of petroleum systems. Herein two geologically distinct organic-rich sedimentary formations are explored utilising trace elements, and rhenium-osmium (Re-Os) and nickel (Ni) isotope systematics. Additionally, this thesis is the first study to investigate the behaviour of Ni isotope systematics in organic-rich marine sediments. Osmium isotope profiling across the Sinemurian-Pliensbachian boundary GSSP indicates that there was a significant contribution of unradiogenic Os to the oceans at this time. Seawater 187Os/188Os(i) values range from ~0.20 – 0.48, becoming increasingly unradiogenic up-section. This progressive change in ocean chemistry is coincident with flooding of the Hispanic Corridor, formed during rifting of the Pangean supercontinent and creation of the Central Atlantic Ocean, evident from sudden levels of faunal exchange between the eastern Pacific and western Tethyan oceans. The Os isotope signal here reflects the onset of hydrothermal activity associated with formation of the Hispanic Corridor. New Ni stable isotope data presented herein for the Sinemurian-Pliensbachian (S-P) GSSP and the Devonian-Mississippian Exshaw Formation, demonstrates that organic-rich marine sediments are characterised by δ60Ni values that are distinct to those of extraterrestrial and abiotic terrestrial samples. Further, the level of Ni isotope fractionation in organic-rich sediments (ranging from ~1.32 ‰ in the S-P sediments, and ~2.04 ‰ in the Exshaw Formation) is far greater than that seen in the other sample suites (ranges of ~0.17 – 0.37 ‰; Cameron et al., 2009). Although there are limited datasets available for comparison at present, the ranges of δ60Ni values for the S-P GSSP and Exshaw Formation are similar (0.28 ± 0.05 to 1.60 ±0.05 ‰ and 0.46 ± 0.04 to 2.50 ± 0.04 ‰, respectively), suggesting that such variation in Ni isotope fractionation may be characteristic of organic-rich sediments. This may be due to complexities that are ubiquitous to the sediment-seawater depositional environment. In addition, trace element ratios utilised to establish depositional paleoredox conditions demonstrate that redox did not exert control on the level of Ni isotope fractionation observed in these sediments. The study herein also demonstrates that thermal maturation of the Exshaw Formation has a negligible effect on Ni isotope systematics in mature source rocks, strongly suggesting that Ni isotopes may have the potential to be developed as an oil-source correlation tool.

The phyllomanganate birnessite is the dominant Mn-bearing phase in oxic marine sediments and through coupled sorption and redox reactions exerts a strong control on the oceanic concentrations of micronutrient trace metals. However, during oxic diagenesis and under mild hydrothermal conditions, birnessite undergoes transformation to the tectomanganate todorokite. The mechanistic details of the transformation are important for the speciation and mobility of metals sequestered by birnessite, and are necessary in order to quantify the role of marine sediments in global trace element cycles. This study provides new insight into the crystallization pathway and mechanism of todorokite formation from birnessite under conditions analogous to those found in marine diagenetic and hydrothermal settings. Using a combined approach employing X-ray diffraction, electron microscopy, infrared spectroscopy, X-ray absorption spectroscopy and wet chemical methods, I propose a new four-stage process for the transformation of birnessite to todorokite, beginning with todorokite nucleation, then crystal growth from solution to form todorokite primary particles, followed by their self-assembly and oriented growth via oriented attachment to form crystalline todorokite laths, culminating in traditional crystal ripening. Furthermore, the results of this study indicate that contrary to current understanding, the bioessential trace metal Ni impedes the transformation of birnessite to todorokite, and is eventually released into sediment porewaters. This mineralogical transformation may therefore provide a benthic flux of Ni and possibly other micronutrient trace metals to seawater. Finally, I find that the uptake of Ni to the phyllomanganate birnessite under varying physiochemical conditions is accompanied by Ni stable isotope fractionation. During fractionation, the light Ni isotope is preferentially sorbed to birnessite, leaving the remaining solution heavy with respect to its Ni isotopic composition. These findings raise important questions about the mechanisms and processes responsible for the heavy δ60Ni isotopic compositions recently measured in marine ferromanganese-rich sediments.