The distribution and stabilisation of dissolved Fe in deep-sea hydrothermal plumes

We have conducted a study of hydrothermal plumes overlying the Mid-Atlantic Ridge near 5 degrees S to investigate whether there is a significant export flux of dissolved Fe from hydrothermal venting to the oceans. Our study combined measurements of plume-height Fe concentrations from a series of 6 CTD stations together with studies of dissolved Fe speciation in a subset of-those samples. At 2.5 kin down plume from the nearest known vent site dissolved Fe concentrations were similar to 20 nM. This is much higher than would be predicted from a combination of plume dilution and dissolved Fe(II) oxidation rates, but consistent with stabilisation due to the presence of organic Fe complexes and Fe colloids. Using Competitive Ligand Exchange-Cathodic Stripping Voltammetry (CLE-CSV), stabilised dissolved Fe complexes were detected within the dissolved Fe fraction on the edges of one non-buoyant hydrothermal plume with observed ligand concentrations high enough to account for stabilisation of similar to 4% of the total Fe emitted from the 5 degrees S vent sites. If these results were representative of all hydrothermal systems, submarine venting could provide 12-22% of the global deep-ocean dissolved Fe budget. (c) 2008 Elsevier B.V. All rights reserved.