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Distribution and redox speciation of dissolved iron on the European continental margin
Author(s) -
Ussher Simon J.,
Worsfold Paul J.,
Achterberg Eric P.,
Laës Agathe,
Blain StÉphane,
Laan Patrick,
de Baar Hein J. W.
Publication year - 2007
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2007.52.6.2530
Subject(s) - oceanography , continental shelf , benthic zone , geotraces , plume , geology , surface water , biogeochemistry , transect , nepheloid layer , oxygen minimum zone , water mass , water column , trace metal , lability , genetic algorithm , seawater , environmental chemistry , upwelling , environmental science , chemistry , metal , ecology , biochemistry , physics , organic chemistry , environmental engineering , biology , thermodynamics
To investigate the biogeochemistry of iron in the waters of the European continental margin, we determined the dissolved iron distribution and redox speciation in filtered (<0.2 µm) open‐ocean and shelf waters. Depth profiles were sampled over the shelf slope southeast of the Chapelle Bank area (47.61°N, 4.24°W to 46.00°N, 8.01°W) and a horizontal surface‐water transect over the shelf and through the English Channel (la Manche) and the southern North Sea (46°N, 8°W to 52°N, 4°E). An abrupt trace‐metal front was found near the shelf slope, indicated by a horizontal gradient of dissolved iron (DFe) and aluminium (DAl), which correlated with changing salinities ( r 2 = 0.572 and 0.528, respectively, n = 92). Labile Fe(II) concentrations varied from <12 pmol L −1 in North Atlantic surface waters to >200 pmol L −1 in the near bottom waters of the shelf break. Labile Fe(II) accounted for ~5% of the dissolved iron species in surface shelf waters (mean 5.0 ± 2.7%), whereas higher Fe(II) fractions (i.e., >8%) were observed near the sea bottom on the shelf break and during a midday solar maximum in surface waters in the vicinity of the Scheldt river plume. Benthic processes (resuspension and diagenesis) constituted important sources of Fe(II) and DFe in this region, and photoreduction of Fe(III) species in shelf waters caused enhanced labile Fe(II) concentrations. These processes increased the lability of iron and its potential availability to marine organisms in the shelf ecosystem.