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Title: The chemistry of iron in hydrothermal plumes
Author: Bennett, Sarah Anne
ISNI:       0000 0001 3460 0934
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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This thesis investigates the role of submarine hydrothermal vents in the global marine Fe budget. While debate continues over the sources of dissolved Fe to the global deep-ocean dissolved Fe budget, it had been presumed, until recently, that all the Fe emitted from hydrothermal vents precipitates and sinks to the seafloor close to the vent source. However, in the open ocean, dissolved Fe exists at concentrations greater than the predicted solubility because of the presence of organically complexed Fe. If similar complexes were formed in the hydrothermal systems then there would be the potential for dissolved Fe export via hydrothermal plumes to the deep-ocean. To investigate the fate of hydrothemally sourced Fe, samples were collected from hightemperature hydrothermal vent-field plumes at 9°N on the East Pacific Rise and at 5°S on the Mid-Atlantic Ridge. The samples from the East Pacific Rise were analysed for Fe and dissolved and particulate organic carbon. Although hydrothermal systems are presumed to be inorganically dominated, elevated concentrations of dissolved organic carbon compared to background seawater were detected in near-field buoyant plumes and the concentration of organic carbon appeared to relate to the total Fe concentration, consistent with the presence of some organic-Fe interaction. Non-buoyant plume samples from the Mid-Atlantic Ridge were analysed for total dissolvable and dissolved Fe and Mn as well as speciation studies on a subset of the dissolved Fe samples using Competitive Ligand Exchange – Cathodic Stripping Voltammetry. The dissolved Fe concentrations in the dispersing plume were higher than predicted from dissolved Fe(II) oxidation rates alone. Further investigation into the speciation of the dissolved Fe revealed the presence of stable Fe-ligand complexes, similar to those detected in the open ocean, but with higher concentrations. If these Fe-ligand complexes were representative of all hydrothermal systems, submarine venting could potentially provide between 11 to 22% of the global deep-ocean dissolved Fe budget. Buoyant plume samples from the same vent site were analysed for total dissolvable and dissolved Fe and Mn as well as particulate Fe, Mn, P, V, Cu, Zn and the rare earth elements. Fe isotopes were also analysed in the particulate fraction, as a potential tool for tracing the biogeochemical cycle of Fe in the ocean. The forms of particulate Fe were elucidated using the particulate trace element data, enabling the isotope fractionation caused by Fe sulfide precipitation to be determined. A diagnostic isotope signature for a potential stabilised dissolved Fe fraction was predicted to be isotopically heavier than the original vent fluid, potentially enabling Fe inputs from hydrothermal vents to be traced throughout the ocean.
Supervisor: German, Christopher ; Statham, Peter Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: GC Oceanography ; QD Chemistry