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| Titel |
New insights on the role of organic speciation in the biogeochemical cycle of dissolved cobalt in the southeastern Atlantic and the Southern Ocean |
| VerfasserIn |
J. Bown, M. Boye, D. M. Nelson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 7 ; Nr. 9, no. 7 (2012-07-27), S.2719-2736 |
| Datensatznummer |
250007196
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| Publikation (Nr.) |
 copernicus.org/bg-9-2719-2012.pdf |
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| Zusammenfassung |
| The organic speciation of dissolved cobalt (DCo) was investigated in the
subtropical region of the southeastern Atlantic, and in the Southern Ocean
in the Antarctic Circumpolar Current (ACC) and the northern Weddell Gyre,
between 34°25´ S and 57°33´ S along the Greenwich Meridian during
the austral summer of 2008. The organic speciation of dissolved cobalt was
determined by competing ligand exchange adsorptive cathodic stripping
voltammetry (CLE-AdCSV) using nioxime as a competing ligand. The
concentrations of the organic ligands (L) ranged between 26 and 73 pM, and
the conditional stability constants (log K'CoL) of the organic
complexes of Co between 17.9 and 20.1. Most dissolved cobalt was organically
complexed in the water-column (60 to >99.9%). There were clear
vertical and meridional patterns in the distribution of L and the organic
speciation of DCo along the section. These patterns suggest a biological
source of the organic ligands in the surface waters of the subtropical
domain and northern subantarctic region, potentially driven by the
cyanobacteria, and a removal of the organic Co by direct or indirect
biological uptake. The highest L:DCo ratio (5.81 ± 1.07 pM pM−1)
observed in these surface waters reflected the combined effects of ligand
production and DCo consumption. As a result of these combined effects, the
calculated concentrations of inorganic Co ([Co']) were very low in the
subtropical and subantarctic surface waters, generally between 10−19
and 10−17 M. In intermediate and deep waters, the South African margins
can be a source of organic ligands, as it was suggested to be for DCo (Bown
et al., 2011), although a significant portion of DCo (up to 15%) can be
stabilized and transported as inorganic species in those DCo-enriched
water-masses. Contrastingly, the distribution of L does not suggest an
intense biological production of L around the Antarctic Polar Front where a
diatom bloom had recently occurred. Here [Co'] can be several orders of
magnitude higher than those reported in the subtropical domain, suggesting
that cobalt limitation was unlikely in the ACC domain. The almost invariant
L:DCo ratio of ~1 recorded in these surface waters also reflected the
conservative behaviours of both L and DCo. In deeper waters higher ligand
concentrations were observed in waters previously identified as DCo sources
(Bown et al., 2011). At those depths the eastward increase of DCo from the
Drake Passage to the Greenwich Meridian could be associated with a large
scale transport and remineralisation of DCo as organic complexes; here, the
fraction stabilized as inorganic Co was also significant (up to 25%) in
the low oxygenated Upper Circumpolar Deep Waters. Organic speciation may
thus be a central factor in the biogeochemical cycle of DCo in those areas,
playing a major role in the bioavailability and the geochemistry of Co. |
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