Mass-transport complexes (MTCs) can significantly modify the seascape by eroding the substrate and depositing thick hetherolithic packages that can behave as hydrocarbon seals or reservoirs. MTC erosion can affect the integrity of underlying reservoir units, and affect subsequent sediment dispersal. Moreover, the irregular seabed profiles resulting from MTC erosion and emplacement can affect the distribution and architecture of subsequent sediments. This study uses a 1900 km2 3D seismic volume from the southern Magdalena Fan, offshore Colombia to investigate: i) the relationship between changes in the size, distribution and provenance of the MTCs and the evolution of tectonic structures; ii) the relationship between and the distribution of MTCs, the geometries of their basal erosion surfaces and their internal characteristics, with the morphology and composition of the seabed, and iii) the effects of MTC-related bathymetric irregularities on the architecture and development of channel-levee complex sets and avulsion lobes. The size, distribution and provenance of MTCs changed through time with the oldest MTCs being smaller (9-100 km2 in area) and sourced and from local collapse of the growing anticlines. Younger MTCs are larger (more than 200-300 km2) and sourced from the shelf, postdating the main phase of folding and faulting in the study area. These changes were used to propose a model of the tectono-stratigraphic evolution of the study area, demonstrating that MTCs can be used to constrain the timing and style of tectonic deformation in time and space. Additionally, the local morphology of the MTC basal surfaces reflects compositional changes in the underlying units, with deeper erosion occurring above channel axes deposits and more subtle slope changes across different levee units. MTC dispersal was influenced by a combination of structural and depositional relief: channel-levee complex sets channelized, diverted or blocked the subsequent mass-flows depending on the orientation of the channel-levee complex sets with respect to the direction of the flow, and the height of the levees with respect to flow thickness. Within the largest MTC, the distribution of the seismic facies was influenced by the underlying bathymetry, with internal contraction occurring updip of bathymetric highs, erosion and bypass above higher gradient slopes, and increased disaggregation towards the margins. Moreover, MTC erosion left behind an erosional remnant ridge upon which a younger channel-levee complex-set developed irregular levee geometries that led to levee collapse and channel avulsion. Map-view geometries and seismic-amplitude extractions suggest that the initial avulsion lobes were mud-prone and evolved to form sand-prone lobes. The distribution, morphology and evolution of the avulsion lobe complexes were influenced by megaclasts protruding on the MTC top surface. This study demonstrates that: i) the architecture, geometries and distribution of MTCs, channel-levee complex sets and avulsion lobes are strongly influenced by bathymetric irregularities on the seabed at various scales; ii) flow-pathways, geometries, distribution and internal characteristics of MTCs can be affected by the properties of the substrate; iii) the stratigraphic evolution of the Magdalena Fan is characterised by the interaction between MTCs and channel-levee complex sets. The learnings from this study can be applied to deeper intervals that are less well imaged and to other margins dominated by MTCs and channel-levee complex sets.

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An important effect in atmosphere and ocean dynamics is the drag exerted by topography, in the form of mountain ranges and individual mountains, on incident flows. Because the scale of topographic variations are usually small compared to the resolution of global-scale numerical models, drag effects must often be parameterised. This thesis aims to understand topographic drag in highly idealised numerical models with a view to demonstrating where efforts in parameterisation may be best directed. Specifically, the thesis considers single-layer and one and one half layered flow (where a single layer lies below an infinitely deep layer of slightly lower density) over topography, inspired by a series of rotating tank experiments. The flow behaviour is strongly affected by the Proude number F of the flow - the ratio of the oncoming flow to the speed of long free gravity waves. The transcritical regime F 1, in which there is a close analogy with compressible gas dynamics, is investigated as a novel limit of the Shallow-Water Equations. Scaling laws for the drag are verified against numerical integrations and various flow regimes for rotating and non-rotating flows delineated. Supercritical flow {F > 1) is also investigated, focusing on both the drag and breaking waves in the far-field, which in the rotating case is shown to depend on a single parameter.

Tanzanian mangrove ecosystems have been, and are presently, influenced by changes in climate and sea level. Fluctuations in these environmental conditions lead to adaptations and changes in ecosystem structure and composition. In this thesis mangrove environments are investigated and used to unravel the Holocene environmental history of the Tanzanian coast. Palaeoecological data from sediments abstracted from three different mangrove locations (the Rufiji Delta, Makoba Bay and Unguja Ukuu) are analysed for fossil pollen and charcoal and combined with stratigraphical investigations and radiocarbon dating allow a detailed environmental reconstruction to be undertaken. The relationship between pollen in surface samples and the surrounding vegetation is used to interpret fossil pollen records. Changes in the relative proportions of mangrove pollen under different inundation regimes are used to reconstruct mangrove dynamics and provide estimates of past sea level changes and infer specific changes in sea level altitude. Palaeoecological records reveal that mangroves in the Rufiji Delta occurred at the central sites from at least ~5600 cal yr B.P. until the late Holocene when mangroves covered the landward site and were succeeded by terrestrial vegetation to the present day. The Zanzibar records reveal fluctuating mangrove compositions from ~8000 cal yr B.P. to the present day with noticeable changes in mangrove composition during the mid Holocene. A reconstructed sea level curve from the three sites document an early-mid to mid Holocene sea level rise from ~ 8000 cal yr B.P. to around 4600 cal yr B.P. with potential highstands at 5800 cal yr B.P. and 4700 cal yr B.P. Sea level fluctuations occurred in the last thousand years with a potential highstand at ~ 530 cal yr B.P. before falling to a lower than present level at ~140 cal yr B.P. The earliest intensive human interactions within the mangroves was recorded in Zanzibar after ~530 cal yr B.P; a time of increased settlements and overseas trade along the Swahili coast. The Rufiji Delta records also demonstrate the impacts of damming and the destruction of mangrove areas for rice cultivation during the last millennium. The palaecological data have helped unravel the environmental history of the Tanzanian coast and have the potential to assist in the development of policies and/or public awareness for the sustainable utilization and management of mangrove ecosystems under predicted future sea level and climate changes.

The Waves, Aerosol, and Gas Exchange Study (WAGES) collected 18 months of near-continuous and autonomous turbulent air-sea flux estimates from the research vessel RRS James Clark Ross. Supporting meteorological and sea-state measurements were also made, with the objective of improving air-sea flux parameterisations. Making turbulence measurements from a ship is technically challenging, due to bias caused by platform motion and airflow distortion. Typically, visual inspection of individual turbulence spectra is needed to quality control eddy covariance flux estimates; for WAGES the sheer volume of data motivated the development of an automated quality control method, to be performed on individual flux cospectra. The application of these tests allowed a robust relationship between the 10 m wind speed and the neutral drag coefficient to be developed, which had previously not been achieved with ship-based covariance measurements alone. This parameterisation is toward the higher end of the range of accepted values, and indicates some wind speed dependence of the Charnock parameter, rather than it being a constant. A detailed investigation of turbulent flow distortion was made; insights into the physics were gained, and a novel correction method for motion-correlated flow distortion was developed and validated. Two major modes of motion-correlated flow distortion of the turbulence were found: one correlated to the pitch, acknowledge in the literature; a second and more powerful mode correlated to the rate of change of the pitch, not acknowledged in any publication. The quality control and bias correction techniques developed for the momentum fluxes were transferred to a preliminary investigation of the sensible and latent heat fluxes. The uncertainty in the latent heat transfer coefficient was reduced considerably by use of the new techniques; however the sensible heat fluxes were dominated by noise, so discarded. The methods and corrections developed in this thesis could be used to reanalyse the turbulent flux measurements from many ship-based campaigns; improving our understanding of the physics of air-sea exchange without need for additional expensive measurements.

Inorganic marine calcium carbonate formation and mineralogy varies significantly concurrent with the solution composition. During the Phanerozoic, due to oscillations in the seawater composition, this resulted in the formation of either dominantly calcite or aragonite. Variations in seawater composition also appear to have influenced the evolution of biomineralizing organisms. Additionally, many organisms utilize amorphous calcium carbonate (ACC) during biomineralization. The occurrence of calcite and aragonite throughout the Phanerozoic and calcium carbonate biomineralization were investigated. This was done by determining the influence of solution chemistry (SO4 and Mg) on calcium carbonate formation, mineralogy and stability via a variety of laboratory and synchrotron based synthesis experiments. During the formation of aragonite and calcite, aqueous SO4 and the Mg/Ca ratio both affect the formation of calcite and aragonite. An increase in aqueous SO4 decreases the Mg/Ca ratio at which calcite is destabilized and aragonite becomes dominant. These results suggest that the models relating seawater chemistry to calcium carbonate formation needs re-evaluation. Abiotic ACC crystallization to vaterite occurs in three stages. In the first stage, ACC crystallizes to vaterite via a spherulitic growth mechanism. The second stage is characterized by surface particle growth at the expense of ACC. Finally, particle growth via Ostwald ripening is the only remaining process. This process can be described as the inorganic analogue to biological ACC crystallization, which is adjusted by organisms to produce their preferred calcium carbonate polymorph and morphology. An increase in SO4 concentration only decreases the spherulitic growth rate and Ostwald ripening, even when rapidcreekite (as an intermediate) and gypsum crystallizes. Finally, SO4 promotes the formation of vaterite. Depending on the formation process this is caused by either the stabilization of vaterite and destabilization of calcite (slow heterogeneous formation), or by the destabilization and inhibition of calcite formation (spherulitic growth).

The short-term background climate variability during the climatically stable latest Miocene to early Pliocene (LM-EP) is not well understood, owing to the lack of continuous, high-resolution climate records. Assessing variability during an interval of long-term climatic stability will constrain how sensitivity of major Earth's system components (Earth system response - ESR) to external radiative forcing has changed through time. This study investigated LM-EP climate, focussing on changes in ESR, El-Nino-Southern-Oscillation state, glacio-eustacy and the Messinian Salinity Crisis (MSC), and the origin of the Late Miocene Carbon Isotope Shift (LMCIS). This project produced the first high-resolution benthic foraminiferal δ18O and δ13C record in the eastern equatorial Pacific (IODP Site U1338) from 8.0-3.5 Ma that resolves all Milankovitch cyclicities. A high-resolution, orbitally-based age model, planktic foraminiferal δ18O, δ13C and Mg/Ca, coccolith-rich 'clumped isotopes' Δ47, spectral analyses and multi-site benthic foraminiferal isotope compilations were also produced. Planktic foraminiferal Mg/Ca sea surface temperatures (SSTs) were ~25 °C. Coccolith-rich Δ47 temperatures were unrealistically cold at ~10-15 °C, reflecting moderate coccolith preservation and vital effects that cause higher Δ47. Site U1338 and 982 combined benthic foraminiferal (δ18O; δ13C) wavelet analyses show moderate ESR from 6.3-4.7 Ma and after 3.7 Ma, but lower ERS from 7.0-6.3 Ma. The δ18O-minimum stage ~5.33 Ma, during long-term minimum δ18O, suggests that glacio-eustacy played a role in the MSC termination. The benthic foraminiferal δ13C compilation confirms that the LMCIS was globally synchronous and caused by a negative shift in oceanic reservoir δ13C, driven by changes in the continental carbon flux (increased sea-floor-spreading / C4-grass expansion). Data syntheses show that global warmth, dominant El-Nino state, high cryosphere sensitivity, lower ice volume and short-term ice sheet variations characterised the LM-EP pre-7.0 and post-5.7 Ma. Stable conditions occurred ~7.0-5.7 Ma, with dominant La-Nina, higher ice volume, low cryosphere sensitivity and lower SSTs.

The aims of this study are to identify the sources of the widespread Holocene deposits of pumice found along the coasts of the North Atlantic region and the age of the source eruptions. Previous research has failed to positively identify the precise source of this pumice. Fieldwork is carried out in Norway and Iceland to obtain pumice pieces for geochemical analysis. Pumice pieces are recovered from Holocene raised beaches and the height of these deposits above sea-level determined. This establishes the existence of substantial local deposits of Holocene pumice on the raised shorelines of north-western Iceland for the first time. The fieldwork in Norway confirms the presence of multiple levels of brown/black/grey pumice on mid-Holocene Norwegian raised beaches and white pumice on late-glacial/early Holocene shorelines. Pumice is also collected from the slopes of the Katla Volcanic System, southern Iceland, which is identified as a possible source of the dacitic pumice. Archaeological pumice, donated by collaborators, from sites in the British Isles is also analysed. The number of archaeological sites where pumice has been recorded is nearly doubled to almost 150. A collaborative project identifies at least 17 silicic tephra layers (SILK layers) which have been produced by the Katla Volcanic System during the Holocene. Geochemical analyses are performed on the majority of these tephra layers. Over 1500 electron probe microprobe analyses (EPMA) and over 200 Secondary Ion Mass Spectrometry (SIMS) analyses are undertaken on pumice and tephra samples. These are the first high quality grain specific analyses carried out on pumice in the North Atlantic. These analyses establish that the majority of the mid- to late-Holocene pumice found in the study areas is dacitic and produced from the same source. Geochemically different and older pumice also occurs in Mesolithic archaeological sites in Scotland. All of the analysed pumice can be correlated to volcanic activity in Iceland.

Consideration of stabilisation techniques is essential in the development of physical models if they are to faithfully represent processes over a wide range of scales. Careful application of these techniques can significantly increase flexibility of models, allowing the computational meshes used to discretise the underlying partial differential equations to become highly nonuniform and anisotropic, for example. This exibility enables a model to capture a wider range of phenomena and thus reduce the number of parameterisations required, bringing a physically more realistic solution. The next generation of fluid flow and radiation transport models employ unstructured meshes and anisotropic adaptive methods to gain a greater degree of flexibility. However these can introduce erroneous artefacts into the solution when, for example, a process becomes unresolvable due to an adaptive mesh change or advection into a coarser region of mesh in the domain. The suppression of these effects, caused by spatial and temporal variations in mesh size, is one of the key roles stabilisation can play. This thesis introduces new explicit and implicit stabilisation methods that have been developed for application in fluid and radiation transport modelling. With a focus on a consistent residual-free approach, two new frameworks for the development of implicit methods are presented. The first generates a family of higher-order Petrov-Galerkin methods, and the example developed is compared to standard schemes such as streamline upwind Petrov-Galerkin and Galerkin least squares in accurate modelling of tracer transport. The dissipation generated by this method forms the basis for a new explicit fourth-order subfilter scale eddy viscosity model for large eddy simulation. Dissipation focused more sharply on unresolved scales is shown to give improved results over standard turbulence models. The second, the inner element method, is derived from subgrid scale modelling concepts and, like the variational multiscale method and bubble enrichment techniques, explicitly aims to capture the important under-resolved fine scale information. It brings key advantages to the solution of the Navier-Stokes equations including the use of usually unstable velocity-pressure element pairs, a fully consistent mass matrix without the increase in degrees of freedom associated with discontinuous Galerkin methods and also avoids pressure filtering. All of which act to increase the flexibility and accuracy of a model. Supporting results are presented from an application of the methods to a wide range of problems, from simple one-dimensional examples to tracer and momentum transport in simulations such as the idealised Stommel gyre, the lid-driven cavity, lock-exchange, gravity current and backward-facing step. Significant accuracy improvements are demonstrated in challenging radiation transport benchmarks, such as advection across void regions, the scattering Maynard problem and demanding source-absorption cases. Evolution of a free surface is also investigated in the sloshing tank, transport of an equatorial Rossby soliton, wave propagation on an aquaplanet and tidal simulation of the Mediterranean Sea and global ocean. In combination with adaptive methods, stabilising techniques are key to the development of next generation models. In particular these ideas are critical in achieving the aim of extending models, such as the Imperial College Ocean Model, to the global scale.