Biogeosciences
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1726-4189
7
2
2010
10.5194/bg-7-455-2010
http://www.biogeosciences.net/7/455/2010/
http://www.biogeosciences.net/7/455/2010/bg-7-455-2010.html
http://www.biogeosciences.net/7/455/2010/bg-7-455-2010.pdf
455
468
2010-02-02
An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean)
F. Chever
G. Sarthou
geraldine.sarthou@univ-brest.fr
E. Bucciarelli
S. Blain
A. R. Bowie
Université Européenne de Bretagne, 35000 Rennes, France
Université de Brest, CNRS, IRD, UMR 6539 LEMAR, IUEM; Technopôle Brest Iroise, Place Nicolas Corpernic, 29280 Plouzané, France
Laboratoire Océanographie Biologique de Banyuls sur Mer, Université Pierre et Marie Curie, Paris 06, quai Fontaulé, 66650 Banyuls sur Mer, France
Laboratoire Océanographie Biologique de Banyuls sur Mer, CNRS, quai Fontaulé, 66650 Banyuls sur Mer, France
Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC), University of Tasmania, Hobart, Australia
Total dissolvable iron (TDFe) was measured in the water column above and in
the surrounding of the Kerguelen Plateau (Indian sector of the Southern
Ocean) during the KErguelen Ocean Plateau compared Study (KEOPS) cruise.
TDFe concentrations ranged from 0.90 to 65.6 nmol L<sup>−1</sup> above the plateau
and from 0.34 to 2.23 nmol L<sup>−1</sup> offshore of the plateau. Station C1
located south of the plateau, near Heard Island, exhibited very high values
(329–770 nmol L<sup>−1</sup>). Apparent particulate iron (Fe<sub>app</sub>),
calculated as the difference between the TDFe and the dissolved iron
measured on board (DFe) represented 95±5% of the TDFe above the
plateau, suggesting that particles and refractory colloids largely dominated
the iron pool. This paper presents a budget of DFe and Fe<sub>app</sub> above the
plateau. Lateral advection of water that had been in contact with the
continental shelf of Heard Island seems to be the predominant source of
Fe<sub>app</sub> and DFe above the plateau, with a supply of 9.7±3.6×10<sup>6</sup>
and 8.3±11.6×10<sup>3</sup> mol d<sup>−1</sup>, respectively. The
residence times of 1.7 and 48 days estimated for Fe<sub>app</sub> and DFe
respectively, indicate a rapid turnover in the surface water. A comparison
between Fe<sub>app</sub> and total particulate iron (TPFe) suggests that the total
dissolved fraction is mainly constituted of small refractory colloids. This
fraction does not seem to be a potential source of iron to the phytoplankton
in our study. Finally, when taking into account the lateral supply of
dissolved iron, the seasonal carbon sequestration efficiency was estimated
at 154 000 mol C (mol Fe)<sup>−1</sup>, which is 4-fold lower than the previously
estimated value in this area but still 18-fold higher than the one estimated
during the other study of a natural iron fertilisation experiment, CROZEX.
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