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Iron is an essential micronutrient for the metabolism of marine organisms and impacts on primary productivity and hence indirectly on climate change. The dominant source of iron to the sea surface in open ocean regions is from the atmosphere by aeolian dust transport but the solubility of iron from dust is poorly constrained. In this thesis, chemical and physical factors impacting on the process of dust dissolution and iron release in seawater were investigated using FI-CL detection. A manual FI manifold was automated and optimised for the determination of iron, at nanomolar concentrations, released from aerosols in seawater. The limit of detection was 0.04 ± 0.03 nM and the precision (rsd) ranged from 0.2 to 10.8%. Protocols, maintenance find troubleshooting sections were documented for effective utilisation o f the technique. A seawater treatment system to produce low DOC (dissolved organic carbon) and dFe (dissolved iron) seawater was adapted and optimised. This UV photo-oxidation system was poorly efficient in removing DOC (-40%), complexing ligands (~60%) and dFe (apparent removal 90%). An autosampler was designed, validated, and integrated with an incubation system for sub-sampling during dissolution experiments of aerosol iron in seawater. Fast release of iron f r om the aerosol particles occurred within the first 2 h, followed by a decrease over 1 day. Preliminary experiments w i t h UV-irradiated seawater exhibited lower solubilities compared w i t h non UV-irradiated seawater. High dust concentrations gave lower final solubilities compared with low dust concentrations. A 24 h kinetic study was carried out using NIST 1648 under contrasting light and dark regimes. Dissolution of the endmember under dark conditions released 0.36% of the iron whilst the addition of 20 nM to 200 nM Desferrioxamine B (DFOB) stimulated a release of 0.90 to 1.6%. In light, the release of iron was 0.50% with aerosol, whilst the addition of DFOB (20 nM) induced an adsorption (-1.18%). Iron release from aerosol samples from three sites around the Eastern Mediterranean: Erdemli, Tel-Shikmona and Heraklion was determined in a NATO funded project. The solubility of contrasting aerosol populations from crustal and anthropogenic sources was investigated. Crustally derived aerosol samples exhibited a variable kinetic profile of iron release with an average of maximum solubility of 0.39 ± 0.52%. The anthropogenically influenced aerosol samples exhibited consistent kinetic profiles (fast release < 2 h) with an average of maximum solubility of 10.6 ± 8.9%. From these results, an approximation of the atmospheric dry inputs of soluble iron in seawater to the Levantine Basin was calculated for the first time, ranging from 804 ± 910 t for the Northern Levantine Basin to 2,670 ± 3,050 t for the Southern Levantine Basin.

Oxygenated Volatile Organic Compounds (OVOCs) are low molecular weight (Cl-C3 compounds), volatile species that include alcohols, aldehydes and ketones. They are ubiquitous throughout thetroposphere where they alter the oxidative capacity of the atmosphere and influence the global ozone budget. The role of the ocean in the cycling of OVOCs remains largely unanswered due to a paucity of water measurements. Thisis . partly due to analytical difficulties in extracting these labile species from solution. Their presence at trace (nanomolar) concentrations and their high solubility makes efficient extraction from solution challenging. This thesis reviews the global importance and the current understanding of the OVOCs and highlights the uncertainty created from a paucity of oceanic measurements. It also details the available analytical capabilities for analysing these species, both in air and water to provide a platform from which to start method development. Developmental work was undertaken in order to design and validate two separate analytical techniques for the extraction of OVOCs from seawater: I) A Membrane Inlet - Proton Transfer Reaction / Mass Spectrometer (MI-PTRlMS) was optimised for the quantification of methanol, acetaldehyde and acetone in seawater, 2) a Purge andTrap- Gas Chromatography / Flame Ionisation Detection (P&T-GCIFID) system was developed for the extraction of ethanol, l-propanol, 2-propanol, propanal, acetone and acetaldehyde. Their independent capabilities are discussed as well as the advantages of their simultaneous use to provide maximum information regarding OVOC content within a sample. These techniques were deployed on two research cruises to as~ess the importance of an upwelling region and also to determine the spatial variability of both the concentration and flux of OVOCs in the Atlantic Ocean. The methods that have been developed during this research have increased the available data on OVOC concentrations in seawater and have shown that the ocean is important in the cycling of these trace gases.

Acrylic acid in the marine environment is thought to originate mainly from the algal osmolyte dimethylsulphoniopropionate (OMSP). Enzymatic cleavage of this precursor has shown to produce the climate active sulphur gas dimethylsulphide (OMS) and acrylic acid. Whereas OMS and DMSP have attracted a lot of scientific interest over the years, the roles and fate of acrylic acid in the marine environment are poorly understood. To investigate these in more detail, an HPLC method has been developed which allows the direct analysis of acrylic acid in seawater. The method has a detection limit of 5-1 OnM and enables differentiation between the dissolved and particulate fractions of acrylic acid. This allowed an in-depth study into the acrylic acid production characteristics of several Emiliania huxleyi strains during growth and senescence and their subsequent classification into high and low acrylic acid producers. Grazing and viral lysis of OMSP-containing cells increases the production of OMS. The concomitant formation of acrylic acid in these processes has often been assumed and laboratory experiments now confirmed this hypothesis. Further research focused on the suggested grazer deterrent effects of acrylic acid and experiments with the microzooplankton grazer Oxyrrhis marina indicated that these were highly dependent on length and levels of exposure. Whilst high acrylate additions to cultures of 0. marina and its prey Dunaliella tertiolecta increased grazer growth rates in the short term (12-24 hours), they resulted in grazing and growth rate reductions in the long-term (1-5 days). Field studies investigated the occurrence of acrylic acid in the natural environment. During a research cruise in the Norwegian and Greenland Sea depth profiles were taken which show for the first time the distribution of this compound within the water column. A mesocosm experiment emphasised the importance of bacterial communities in controlling acrylic acid levels in the natural environment and identified it as an important carbon source for bacterial growth.

This project investigates how isotope systems respond to changes in continental weathering processes and the consequences for the chemical composition of the oceans. Both experimental and natural data indicate that Li and Mg stable isotope systems preserve information on the mineral reactions controlling water chemistry. Dissolution experiments indicate that primary mineral formation has little effect on Li, but does fractionate the isotopes of Mg, whereas secondary mineral formation involves preferential uptake of the lighter isotopes of both Li and Mg. Glacial regions have low chemical weathering rates so their rivers should, in principal, have Li isotope compositions (δ⁷Li) that are similar to those of the underlying rock.