Organic Matrices Help Preserve Iron At Sea

Hot-water plumes gushing into the ocean through seafloor hydrothermal vents have historically been viewed as inorganic systems. But new research suggests that the underwater geysers pull in organic material from nearby flora and fauna, a finding with implications for the geochemical cycling of nutrients (Nat. Geosci., DOI: 10.1038/ngeo433). A research team led by Brandy M. Toner, formerly of Woods Hole Oceanographic Institution and now of the University of Minnesota, Twin Cities, examined samples of particulate matter collected from the Tica vent at the East Pacific Rise by using scanning transmission X-ray microscopy and near-edge X-ray absorption fine structure spectroscopy. By weight, the samples contained an average of 6.7% particulate organic carbon, which likely came from biological debris. Some of the organic carbon was in the form of polymer-like matrices that appear to be composed of lipids, polysaccharides, and proteins. The matrices also incorporate Fe(II) and Fe(III), with the iron likely bound to organic functional groups through sorption or complexation. The researchers propose that the matrices prevent oxidation and precipitation of Fe(II), perhaps increasing its bioavailability as a deep-sea nutrient.