Dissolved Fe and Fe binding ligand concentrations at the hydrothermal vent fields in the Coriolis Troughs, New Hebrides Island Arc

It is globally accepted that hydrothermal vent fluids are highly enriched in Fe compared to the surrounding seawater and for long it was believed that the majority of the dissolved Fe is precipitated either directly out of the fluid with seawater contact or from the plume within a short distance.

Recent research at other deep-sea hydrothermal vents has shown, however, that organic ligands are able to keep Fe soluble and therefore facilitating its transport into the open ocean. This is important since Fe is also considered a limiting factor for primary production in large parts of the world`s surface ocean. The New Hebrides Island Arc is not studied well with respect to the fluid chemistry of its numerous vents. Up until now, no data is published for the crucial micronutrient Fe in these fluids. Several hydrothermal vent fluids, divided into mixing zone, outlet and pure fluid as well as one hydrothermal plume from the Coriolis Troughs have been analyzed with respect to total dissolved Fe (dFe) and Fe binding ligands (FeL), using competitive ligand exchange - adsorptive cathodic stripping voltammetry (CLE - AdCSV) with Salicylaldoxime as the artificial ligand.

Our dFe data for the hydrothermal plume show concentrations ranging from 9.6 nM to 30.1 nM, being highly enriched compared to the surrounding seawater. Good correlation is observed between dFe and turbidity, which can be used as a proxy for hydrothermal plumes. Hydrothermal fluid samples collected near and directly from the vent outlet show total dissolved Fe concentrations varying from 0.46 µM up to 380 µM, respectively. We find enriched organic ligand concentrations in the plume samples as well as in the samples taken near the hydrothermal vent outlets. Pure hydrothermal fluid samples with an in-situ temperature of up to 370 °C show different ligand properties than low to mid temperature samples.