Abstract
The bioavailability of iron in seawater filtered through a 0.025-μm filter was investigated using 59Fe-labeled iron uptake by the macroalga Laminaria japonica (Areschoug: Phaeophyta) (collected in the northern Japan Sea 1993) as an assay. About 80% of the iron in the 0.025-μm filtered coastal seawater was soluble and/or small colloidal organically bound iron, associated with natural organic ligands forming complexes with ferric ion. After decomposition of the organic matter by ultraviolet (UV) irradiation, 55% of the iron addition [or 0.6 nM, nearly the concentration of Fe(OH) +2 in equilibrium with amorphous hydrous ferric oxide in seawater at pH 8.0] in the 0.025-μm filtered coastal seawater was taken up by the macroalga. Since the iron concentrations in the 0.025-μm filtered coastal seawater are 0.1 to 2.0 nM and only 0.6 nM of the iron is likely available to biota over 1 to 2 d, we suggest that only small amounts of bioavailable iron exist in coastal seawater not affected by inflow from land and that a significant fraction of dissolved (<0.025 μ) iron occurs in forms, such as organic iron complexes, other than the simple hydroxo-complex species predicted by thermodynamic models.
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Communicated by T. Ikeda, Hiroshima
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Suzuki, Y., Kuma, K. & Matsunaga, K. Bioavailable iron species in seawater measured by macroalga (Laminaria japonica) uptake. Marine Biology 123, 173–178 (1995). https://doi.org/10.1007/BF00350337
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DOI: https://doi.org/10.1007/BF00350337