Turbidity currents are one of the main processes by which sediment is moved from the continental shelf to the deep ocean. They are a potential environmental hazard and they form a significant component of the stratigraphic record. Computational modelling is an important tool for understanding turbidity current dynamics, for augmenting experimental analyses, and for interpreting data that is collected in the field. This work begins by presenting a depth-averaged turbidity current model that is differentiated to facilitate the use of gradient-based optimisation algorithms. These optimisation algorithms are applied in selecting model parameters to best fit model output with data obtained in the field. To the best of the author's knowledge this is the first published work where optimisation of input parameters is applied to turbidity current modelling. The work also presents the first high resolution three-dimensional simulation of a turbidity current using the finite element method. One of the key benefits of the finite element method is the ability to easily accommodate complex domain geometries. As such this model is uniquely capable of producing high resolution simulations of turbidity currents in unconstrained complex domains. Methods of reducing the computational cost of these very expensive simulations are explored. The use of Large Eddy Simulation is shown to provide some improvements at moderate simulation resolutions. Unstructured mesh optimisation is shown to reduce the cost of these simulations by approximately two orders of magnitude when compared to a fixed mesh simulation. The savings afforded by the use of these techniques make the problem tractable using finite elements and will enable simulation of turbidity currents in complex and expansive domains where DNS modelling was previously unachievable.

Observations and climate models suggest significant decadal variability within the North Atlantic subpolar gyre (NA SPG), though observations are sparse and models disagree on the details of this variability. Therefore, it is important to understand 1) the mechanisms of simulated decadal variability, 2) which parts of simulated variability are more faithful representations of reality, and 3) the implications for climate predictions. Here, we investigate the decadal variability in the NA SPG in the state-of-the-art, high resolution (0.25◦ ocean resolution), climate model ‘HadGEM3’. We find a decadal mode with a period of 17 years that explains 30% of the annual variance in related indices. The mode arises due to the advection of heat content anomalies, and shows asymmetries in the timescale of phase reversal between positive and negative phases. A negative feedback from temperature-driven density anomalies in the Labrador Sea (LS) allows for the phase reversal. The North Atlantic Oscillation (NAO), which exhibits the same periodicity, amplifies the mode. The atmosphere-ocean coupling is stronger during positive rather than negative NAO states, explaining the asymmetry. Within the NA SPG, there is potential predictability arising partly from this mode for up to 5 years. There are important similarities between observed and simulated variability, such as the apparent role for the propagation of heat content anomalies. However, observations suggest interannual LS density anomalies are salinity-driven. Salinity control of density would change the temperature feedback to the south, possibly limiting real-world predictive skill in the southern NA SPG with this model. Finally, to understand the diversity of behaviours, we analyse 42 present-generation climate models. Temperature and salinity biases are found to systematically influence the driver of density variability in the LS. Resolution is a good predictor of the biases. The dependence of variability on the background state has important implications for decadal predictions.

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An increase of heavy metals in the natural environment, as a result of human development activities, may lead to further impacts on environment and human health. The project aim was to investigate the potential impact of heavy metal sources on the marine sediment at Sohar Industrial Port (SIP) and nearby coastal regions. SIP was established in 1999 and this is the first comprehensive evaluation of heavy metal pollution at the port. The research focused on the levels of Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, V, Zn , Hg, As and Sn over a period of two years. The concentration of anions F, Br, Cl and SO4 in the sediment was also evaluated. The research has, based on published literature, evaluated the public and environmental issues at SIP and nearby regions area. A theoretical fingerprinting technique was used to establish sources of pollution in the SIP region using a combination of field data, laboratory analyses of samples and statistical modeling techniques. Results from the study indicate that concentration of heavy metals was significantly higher at the SIP than in the nearby coastal regions. The data indicated that Cd, Cr, Cu, Ni, Pb, Zn, Hg and As sediment concentrations exceeded levels for International Sediment Quality Guidelines (ISQG) values from USA, Canade, Holland, Australia and New Zealand . Heavy metals that exceed ISQG provide higher potential risks of contamination and may cause human health problems at the SIP and surrounding areas. Potential sources of pollution at SIP include petrochemical industries, various metal processing industries, cooling water outfalls, dust emissions from industries and open hazardous storage sites. Consideration needs to be given to the use of addition new technologies for cleaning of pollution in the environment around SIP. The project proposes development of policies and strategies to mitigate and prevent further sediment contamination at SIP and nearby regions.

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The biodegradation of urea by phototrophic and heterotrophic micro organisms and the urea sea water concentration were investigated in relation to the microbial population, inorganic sources of nitrogen and the hydrography of the Elbe estuary and Southern German Bight during three cruises (HGL Cruises) from the end of July to the end of September 1976. During the HGL cruises and a preliminary investigation in Beaumaris Bay and the Menai Strait, no evidence was found to suggest that land derived urea was an important contributor to sea water urea concentration. In situ production seems likely to be a major source of urea. Urea contributes an ecologically significant amount to the total nitrogen' (ammonium, nitrate, nitrite and urea-N) in the Elbe estuary and S. German Bight. Urea-N concentrations in the latter water, although showing greater spacial variation than the inorganic nitrogen, often exceeded the concentrations of the inorganic nitrogen. Urea concentrations were highest during periods of greatest biological activity (Cruise HGL I:July-August) and decreased as the year advanced. Both phototrophic and heterotrophic micro organisms are important in the biodegradation of urea and rates of degradation were highest during the time of highest biological activity (Cruise HGL I: July-August), phototrophic urea degradation predominating in the Elbe estuary while heterotrophic degradation generally predominated in offshore waters. A complex relationship may exist between the urea producers (possibly zooplankton) and urea degraders as well as between the phototrophic and heterotrophic micro organisms. Distinct water regimes (the Elbe, Coastal and North Sea regimes) of different physical characteristics, often separated by frontal regions were encountered on the HGL cruises. The distribution of the micro organisms and sea water urea concentrations were related to the hydrography and these in turn affected the distribution of rates of urea biodegradation. Urea assimilation indices indicated that in the stratified North Sea regime, containing low inorganic nitrogen, bacteria were more effective urea degraders than phytoplankton. Cellular ATP: cellular C ratios may be a useful indicator of physiological activity and environmental stress. Urea assimilation indices and cellular ATP: cellular C ratios may indicate that the micro organisms in the Elbe estuary are under greater environmental stress than those in the more offshore waters of the North sea regime.

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No description available.

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No description available.