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Article
Iron Colloids Dominate Sedimentary Supply to the Ocean Interior
Proceedings of the National Academy of Sciences
  • William B. Homoky, University of Leeds
  • Tim M. Conway, University of South Florida
  • Seth G. John, University of Southern California
  • Daniela König, University of Liverpool
  • FeiFei Deng, University of Oxford
  • Alessandro Tagliabue, University of Liverpool
  • Rachel A. Mills, University of Southampton
Document Type
Article
Publication Date
1-1-2021
Digital Object Identifier (DOI)
https://doi.org/10.1073/pnas.2016078118
Disciplines
Abstract

Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a “rusty source”) that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.

Citation / Publisher Attribution

Proceedings of the National Academy of Sciences, v. 118, issue 13, art. e2016078118

Citation Information
William B. Homoky, Tim M. Conway, Seth G. John, Daniela König, et al.. "Iron Colloids Dominate Sedimentary Supply to the Ocean Interior" Proceedings of the National Academy of Sciences Vol. 118 Iss. 13 (2021)
Available at: http://works.bepress.com/tim-conway/27/