Iron supply from the Mid Atlantic Ridge to the North Atlantic ocean

Maeve Carroll Lohan, University of Southampton, Ocean and Earth Science, Southampton, SO14, United Kingdom, Alastair J.M. Lough, University of Southampton, Ocean and Earth Sciences, National Oceanography Centre, Southampton, United Kingdom, David Gonzalez Santana, Institut Universitaire Européen de la Mer, Université de Bretagne-Occidentale, Plouzané, France, Alessandro Tagliabue, University of Liverpool, Liverpool, United Kingdom and Joseph Resing, NOAA/PMEL, Joint Institute for the Study of the Atmosphere and the Ocean, Seattle, WA, United States
Abstract:
Iron (Fe) limits primary productivity in large regions of the worlds oceans. Recent studies have revealed that hydrothermal inputs of iron to the ocean can be detected many thousands of kilometers away from mid-ocean ridges. However, the mechanisms by which hydrothermal vents supply Fe to the deep ocean are poorly understood.

We sampled hydrothermal plumes originating from 10 known vent sites on the Mid-Atlantic Ridge (MAR) with differing geochemistry to assess the chemical stability of Fe released from each site. Hydrothermal dFe is dispersed to the West of the MAR into the N. Atlantic as well as North to South along the ridge axis. Within the MAR dFe was always greater than deep open ocean concentrations indicative of the spreading of plumes within the ridge. Hydrothermal plume dFe was predominantly colloidal (dFe-sFe = cFe) decreasing as a fraction of dFe with distance from the hydrothermal source suggesting either a loss of cFe or exchange between size fractions. Understanding this exchange and the formation of particulates is critical to constraining the longevity of hydrothermal Fe in the deep ocean. Near Edge X-Ray Adsorption Fine Structure (NEXFAS) on particles showed changes in iron (II) and iron (III) speciation as particles were dispersed from hydrothermal plumes.

Our study highlights the ubiquity of elevated Fe concentrations along the MAR and how differing geochemistry influences the hydrothermal flux of dFe to the ocean. We compared Fe data to conservative δ3He to constrain the longevity of hydrothermal Fe in the North Atlantic.