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The biogeochemical cycle of dissolved cobalt in the Atlantic and the Southern Ocean south off the coast of South Africa
Bown, J.; Boye, M.; Baker, A.; Duvieilbourg, E.; Lacan, F.; Le Moigne, F.; Planchon, F.; Speich, S.; Nelson, D.M. (2011). The biogeochemical cycle of dissolved cobalt in the Atlantic and the Southern Ocean south off the coast of South Africa, in: 43rd international Liège colloquium on ocean dynamics "Tracers of physical and biogeochemical processes, past changes and ongoing anthropogenic impacts" - May 2-6, 2011. pp. 2
In: (2011). 43rd international Liège colloquium on ocean dynamics "Tracers of physical and biogeochemical processes, past changes and ongoing anthropogenic impacts" - May 2-6, 2011. GHER, Université de Liège: Liège. 156 pp., meer
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  • Bown, J.
  • Boye, M.
  • Baker, A.
  • Duvieilbourg, E.
  • Lacan, F.
  • Le Moigne, F.
  • Planchon, F., meer
  • Speich, S.
  • Nelson, D.M.
Abstract
    Dissolved cobalt (DCo) concentrations were measured by flow-injection analysis and chemiluminescence detection in filtered (0.2 µm), acidified and UV-digested samples at 12 deep stations in order to resolve the several biogeochemical provinces of the Antarctic Circumpolar Current and to assess the vertical and frontal structures in the Atlantic sector of the Southern Ocean. DCo concentrations ranged from 5.73 ± 1.15 pM to 72.9 ± 4.51 pM. The distribution of DCo was nutrient-like in surface waters of the subtropical domain with low concentrations in the euphotic layer due to biological uptake. The biological utilization of dissolved cobalt was proportional to that of phosphate in the subtropical domain with a DCo:Phosphate depletion ratio of 44 µM/M. In deeper waters the distribution indicated remineralization of DCo and inputs from the margins of South Africa with lateral advection of enriched intermediate and deep waters to the southeastern Atlantic Ocean. In contrast the vertical distribution of DCo changed southward, from a nutrient-like distribution in the subtropical domain to scavenged-type behaviour in the domain of the Antarctic Circumpolar Current and conservative distribution in theWeddell Gyre. There the cycle of DCo featured low biological removal by Antarctic diatoms with input to surface waters by snow, removal in oxygenated surface waters, and dissolution and stabilization in the low-oxygenated Upper Circumpolar Deep Waters. DCo distributions and physical hydro-dynamics features also suggest inputs from the Drake Passage and the southwestern Atlantic to the 0° meridian along the eastward flow of the Antarctic Circumpolar Current. Bottom enrichment of DCo in the Antarctic Bottom Waters was also evident, together with increasing water-mass pathway and ageing, possibly due to sediment resuspension and/or mixing with North Atlantic Deep waters in the Cape Basin. Overall atmospheric input of soluble Co by dry aerosols to the surface waters was low but higher in the ACC domain than in the northern part of the section. At the highest latitudes, it is possible that snowfall could be a source of DCo to surface waters. Tentative budgets for DCo in the mixed layer of the subtropical and the ACC domains have been constructed for each biogeochemical region encountered during the cruise. The estimated DCo uptake flux was found to be the dominant cobalt flux along the section. This flux decreases southward, which is consistent with the observations that DCo shows a southward transition from nutrient-like towards conservative distribution in the mixed layer.
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