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Iron is an essential micronutrient for the growth of planktonic species. It is an integral element of numerous enzymes and proteins with important functions in photosynthesis and respiratory electron transport. In contrast to iron, hydrogen peroxide (H202) is ubiquitous in seawater. Phytoplankton are known to generate reactive oxygen species (ROS) such as superoxide and H202 . This production, in conjunction with membrane bound reductases, may affect an organism's ability to access nutrients such as iron. The work presented in this thesis describes the development and optimisation of sensitive flow injection-chemiluminescence techniques to assess redox processes at the cellular level and their application to investigate marine processes. Two flow injection methods, one based on direct sample injection and another involving the preconcentration of iron, were used to determine iron (II) and dissolved iron and assess potential interference from a number of metals and H202. The results demonstrated the increased oxidation of Fe(II) in the presence of H202 (half life reduced from 10.4 to 3.5 min at 50 nM H202) and confirmed the ability of the pre-concentration method to remove this matrix interference. The accuracy and precision of the pre-concentration method were confirmed through analysis of samples collected on two international intercomparison studies. The results demonstrated that the method was precise (- 8 %RSD) and provided a suitably low limit of detection (17 pM) for the determination of dissolved iron. Dust deposition is an important source of iron to remote open ocean regions. The solubility of iron and aluminium in North Atlantic waters was assessed through an on-deck dissolution experiment. Calculated solubilities of iron released from six differing dust samples were low and varied from 0.001 to 0.04 %, whereas the release of aluminium ranged from 0.06-9.0 %. Solubility was inversely correlated with particle concentration, where higher solubility was observed for lower particle concentrations. A versatile and adaptable FI system was developed, with a low detection limit (0.4 - 1.3 nM), excellent precision (1.1-1.8 %RSD) and the capability of sensitive real-time determination of H202 over a wide dynamic range. The results from laboratory based assays using a novel in-line filter approach demonstrated H202 production by the diatom species Thalassiaira ueiss weissflogii with observed concentrations in the range 30- 100 nM. In addition, through field studies carried out in two different oceanic regions (English Channel and Ross Sea), a previously unreported correlation between phytoplankton biomass and surface H20 1 concentrations was observed. The FI-CL instrumentation for the determination of Fe(II) was successfully adapted and optimised for the continuous in-line measurements of Fe(II) generated by diatoms. This technique provided a low detection limit (11 pM) and excellent precision (6.3 ± 3.2 % RSD). In further laboratory based assays with T. ueissflogii, preliminary results indicated pM changes in Fe(II) generation following the reduction of organically bound Fe(Ill).

Salmon farming is a major industry in many Scottish sea lochs. Although the impact of salmon farming and pathways of several farm wastes have been studied extensively, there has been little research into the fate of metals originating from fish farms. This thesis investigates the influence of salmon farming on sediment biogeochemical conditions, with particular reference to the cycling, interactions, and effects of metals in farm sediments of Scottish sea lochs. Scottish sea lochs are fjordic systems, and have a defined set of physical processes occurring within them that depend on topographical characteristics of the sea loch and the influence of external forces. The most common definition of a fjord, also know as a sea loch, is “a deep, high-latitude estuary which has been (or is presently being) excavated or modified by landbased ice” (Syvitski et al. 1987). The established opinion of their origin is that fluvial action along fault lines allowed subsequent glaciers to follow this path of least resistance, leading to major excavation (Skei et al. 2003). Fjords are found in all northern and southern regions of the earth that were once ice-covered, but this review will focus on the sea loch (fjordic) systems of western Scotland.

The aim of this study was to improve our understanding of the marine iron cycle using a newly implemented technique to measure dissolved iron in seawater. The setting up of a flow-injection analyser with chemiluminescence detection (FIACL) for Fe(II) proved to be non-trivial. Extensive work was undertaken to solve problems relating to our limited level of understanding of the CL reaction, and the variable behaviour of the resins prepared to preconcentrate iron. An analyser for Fe(II)+(III) was optimised, and careful assessment of data demonstrated the high quality of the information interpreted in this study, from the Celtic Sea shelf edge (Northeast Atlantic), and from the North Scotia Ridge (Southern Ocean). The distribution of iron at the Celtic Sea shelf edge was examined, and was used to provide a conceptual framework for future studies. Dissolved Fe (< 0.4 µm) concentrations were measured in samples from nine vertical profiles taken across the continental slope (160 – 2950 m water depth). Dissolved iron concentrations varied between 0.2 and 5.4 nM, and the resulting detailed section showed evidence of a range of processes influencing the iron distributions. The presence of elevated levels of dissolved Fe near the seafloor was consistent with release of Fe from in situ particulate organic matter remineralisation at two upper slope stations, and possibly of pore water release upon resuspension on shelf. Lateral transport of dissolved iron was evident in an intermediate nepheloid layer and its advection along an isopycnal. Surface waters at the shelf break also showed evidence of vertical mixing of deeper iron-rich waters. The data also suggest some degree of stabilisation of relatively high concentrations of iron, presumably through ligand association or as colloids. The possibility of iron limitation of phytoplankton at the shelf edge was not ruled out despite obvious depletion of nitrate. This study supports the view that export of dissolved iron laterally to the ocean’s interior from shelf and coastal zones may have important implications for the global budget of oceanic iron. A set of surface samples collected on a survey between the Falkland Islands and South Georgia were analysed for total dissolvable iron. Results suggested a source of benthic iron near South Georgia. A shift in photo-physiology of phytoplankton towards South Georgia was probably influenced by the transition from iron-limited to iron-replete populations. These results therefore strongly support the hypothesis that South Georgia may be a "pulse-point" of iron to high-nutrient low-chlorophyll waters.