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Dissolved iron in the vicinity of the Crozet Islands, Southern Ocean

Research output: Contribution to journalArticlepeer-review

  • Helene Planquette
  • Peter J. Statham
  • Professor Gary Fones
  • Matthew A. Charette
  • C. Mark Moore
  • Ian Salter
  • Florence H. Nedelec
  • Sarah L. Taylor
  • M. French
  • A. R. Baker
  • N. Mahowald
  • T. D. Jickells
The annual phytoplankton bloom occurring north of the Crozet Plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high-nutrient low-chlorophyll (HNLC) conditions normally associated with the Southern Ocean. Therefore, during CROZet natural iron bloom and EXport experiment (CROZEX), a large multidisciplinary study performed between November 2004 and January 2005, measurements of total dissolved iron (DFe≤0.2 μm) were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples.DFe concentrations were determined by flow injection analysis with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD) catalytic spectrophotometric detection. DFe concentrations varied between 0.086 and 2.48 nM, with low values in surface waters. Enrichment of dissolved iron (>1 nM) at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron. Waters farther north also appear to be affected by this input of coastal and shelf origin, although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of ∼0.07 nM km−1 at the time of sampling. Using lateral and vertical diffusion coefficients derived from Ra isotope profiles and also estimates of atmospheric inputs, it was then possible to estimate a DFe concentration of ∼0.55 nM to the north of the islands prior to the bloom event, which is sufficient to initiate the bloom, the lateral island source being the largest component. A similar situation is observed for other Sub-Antarctic Islands such as Kerguelen, South Georgia, that supply dissolved iron to their surrounding waters, thus enhancing chlorophyll concentrations.
Original languageEnglish
Pages (from-to)1999-2019
JournalDeep Sea Research Part II: Topical Studies in Oceanography
Issue number18-20
Early online date27 Sep 2007
Publication statusPublished - 2007

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