Iron Speciation in Hydrothermal Plumes

Authors: Jeff Hawkes (National Oceanography Centre,)
Co-authored by industrial partner: No

Type: Thesis

State: Published (Approved)
Published: September 2013

Abstract: " This thesis considers the speciation of the transition metal iron (Fe) in hydrothermal vent plumes. Hydrothermal inputs have recently been recognised as important in the oceanic cycling of Fe, but understanding of the chemical forms of Fe in hydrothermal plumes remains very limited. By considering the abundance and distribution of various size and reactivity fractions of Fe in plumes it is possible to better constrain the true impact that hydrothermal Fe may have on ocean biogeochemistry. A reverse titration voltammetric technique was developed to determine Fe binding ligands in seawater when ligands were over-saturated by high concentrations of Fe, and Fe binding ligands and Fe size fractions were assessed in two hydrothermal plumes in the Southern Ocean. The results indicated that at least 7.5% of total vented hydrothermal Fe was present in association with labile complexes in the plume, which may have been organic, inorganic or mixed in their nature. These complexes would be available for transport into the deep ocean, representing an important source of bioavailable Fe to marine environments. A large portion of Fe in the plumes was in the colloidal size fraction, leading to the conclusion that weak colloidal flocculates are important in the distribution of hydrothermal Fe. The distribution and speciation of Fe was assessed in an island arc caldera. Fe oxy-hydroxide colloids were important in this environment, suggesting that the acid rich and often shallow hydrothermal venting found at island arcs should provide Fe as a micronutrient to surface waters. The interaction of Fe and several elements was assessed in the particulate phase in the three vent environments. Oxyanion (e.g. phosphorus) scavenging with Fe oxy-hydroxides was increased in the island arc and sulfide dominated vent sites, suggesting that factors other than phosphate concentration, such as Fe oxidation rate, could be important in how hydrothermal Fe oxy-hydroxides interact with seawater. "

Journal Keywords: Oceanography

Subject Areas: Environment, Materials

Instruments: I18-Microfocus Spectroscopy

Added On: 21/02/2014 07:45

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