Articles | Volume 13, issue 13
Biogeosciences, 13, 3887–3900, 2016
Biogeosciences, 13, 3887–3900, 2016

Research article 06 Jul 2016

Research article | 06 Jul 2016

Potentially bioavailable iron delivery by iceberg-hosted sediments and atmospheric dust to the polar oceans

Robert Raiswell1, Jon R. Hawkings2, Liane G. Benning1,3, Alex R. Baker4, Ros Death2, Samuel Albani5,a, Natalie Mahowald5, Michael D. Krom1,6, Simon W. Poulton1, Jemma Wadham2, and Martyn Tranter2 Robert Raiswell et al.
  • 1Cohen Biogeochemistry Laboratory, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
  • 2Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK
  • 3GFZ, German Research Centre for Geosciences, Telegrafenberg, 11473 Potsdam, Germany
  • 4Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  • 5Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, USA
  • 6Department of Marine Biology, Haifa University, Haifa, Israel
  • anow at: the Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

Abstract. Iceberg-hosted sediments and atmospheric dust transport potentially bioavailable iron to the Arctic and Southern oceans as ferrihydrite. Ferrihydrite is nanoparticulate and more soluble, as well as potentially more bioavailable, than other iron (oxyhydr)oxide minerals (lepidocrocite, goethite, and hematite). A suite of more than 50 iceberg-hosted sediments contain a mean content of 0.076 wt % Fe as ferrihydrite, which produces iceberg-hosted Fe fluxes ranging from 0.7 to 5.5 and 3.2 to 25 Gmoles yr−1 to the Arctic and Southern oceans respectively. Atmospheric dust (with little or no combustion products) contains a mean ferrihydrite Fe content of 0.038 wt % (corresponding to a fractional solubility of  ∼  1 %) and delivers much smaller Fe fluxes (0.02–0.07 Gmoles yr−1 to the Arctic Ocean and 0.0–0.02 Gmoles yr−1 to the Southern Ocean). New dust flux data show that most atmospheric dust is delivered to sea ice where exposure to melting/re-freezing cycles may enhance fractional solubility, and thus fluxes, by a factor of approximately 2.5. Improved estimates for these particulate sources require additional data for the iceberg losses during fjord transit, the sediment content of icebergs, and samples of atmospheric dust delivered to the polar regions.

Short summary
Iron is an essential nutrient for plankton growth. One important source of iron is wind-blown dust. The polar oceans are remote from dust sources but melting icebergs supply sediment that contains iron which is potentially available to plankton. We show that iceberg sediments contain more potentially bioavailable iron than wind-blown dust. Iceberg sources will become increasingly important with climate change and increased plankton growth can remove more carbon dioxide from the atmosphere.
Final-revised paper