Abstract
Hydrothermal vent fluids are highly enriched in iron (Fe) compared to ambient seawater, and organic ligands may play a role in facilitating the transport of some hydrothermal Fe into the open ocean. This is important since Fe is a limiting micronutrient for primary production in large parts of the world`s surface ocean. We have investigated the concentration and speciation of Fe in several vent fluid and plume samples from the Nifonea vent field, Coriolis Troughs, New Hebrides Island Arc, South Pacific Ocean using competitive ligand exchange - adsorptive cathodic stripping voltammetry (CLE - AdCSV) with salicylaldoxime (SA) as the artificial ligand. Our results for total dissolved Fe (dFe) in the buoyant hydrothermal plume samples showed concentrations up to 3.86 µM dFe with only a small fraction between 1.1% and 11.8% being chemically labile. Iron binding ligand concentrations ([L]) were found in µM level with strong conditional stability constants up to log K[L],Fe3+ of 22.9. Within the non-buoyant hydrothermal plume above the Nifonea vent field, up to 84.7% of the available Fe is chemically labile and [L] concentrations up to 97 nM were measured. [L] was consistently in excess of Felab, indicating that all available Fe is being complexed, which in combination with high Felab values in the non-buoyant plume, signifies that a high fraction of hydrothermal dFe is potentially being transported away from the plume into the surrounding waters, contributing to the global oceanic Fe budget.
Highlights
Iron (Fe) is an essential micronutrient for all marine organisms
The three samples taken within the plume core are enriched compared to regular seawater and follow the turbidity signal of the CTD water sampler (Figure 4), which can be used as a tracer for hydrothermal plumes
In terms of the various modeling scenarios presented in Resing et al (2015), we found little evidence to suggest that the hydrothermal flux of organic ligands was significantly greater than that of dissolved Fe (dFe), and rather support the theory that only a portion of dFe transport from hydrothermal vent fields is in the form of organic complexes, with the rest present as non-chemically labile nano-particles and colloids
Summary
Iron (Fe) is an essential micronutrient for all marine organisms. Fe is the fourth most abundant element in the earth’s crust (Hans Wedepohl, 1995), dissolved Fe (dFe,
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