Organic complexation of cobalt across the Antarctic Polar Front in the Southern Ocean
Michael J. Ellwood A H , Constant M. G. van den Berg B , Marie Boye C , Marcel Veldhuis D , Jeroen T. M. de Jong E , Hein J. W. de Baar D , Peter L. Croot F and Gerhard Kattner GA National Institute of Water and Atmospheric Research, PO Box 11 115, Hamilton, New Zealand.
B Earth and Ocean Sciences, University of Liverpool, Liverpool, UK.
C LEMAR, CNRS-UMR 6539/IUEM, F-29280 Plouzane, France.
D Netherlands Institute for Sea Research, Texel, The Netherlands.
E Department of Earth and Environmental Sciences, Université Libre de Bruxelles, CP 208, Boulevard de Triomphe B-1050, Brussels, Belgium.
F Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Düsternbrooker Weg 20, D-24105, Kiel, Germany.
G Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany.
H Corresponding author. Email: m.ellwood@niwa.co.nz
Marine and Freshwater Research 56(8) 1069-1075 https://doi.org/10.1071/MF05097
Submitted: 24 May 2005 Accepted: 7 September 2005 Published: 3 November 2005
Abstract
There is compelling evidence to demonstrate that phytoplankton in major regions of the world’s oceans are limited by the availability of certain trace elements, notably iron. Cobalt concentrations in open-ocean waters generally range between 10 and 120 pmol L−1 but such levels were not thought to limit phytoplankton growth. Herein, we present data for total dissolved cobalt and cobalt-complexing ligands for two stations located south (station 200) and north (station 204) of the Antarctic Polar Front (APF) along 20°E in the South Atlantic sector of the Southern Ocean. Results indicate that there was little difference between total cobalt concentrations south and north of the APF, whereas ligand concentrations were significantly higher (15–20 pmol L−1) for the upper water column south of the APF. Productivity in these waters was low at the time of this study; however, numbers of large eukaryotic algal species were higher south of the APF, while north of the APF small eukaryotic and prokaryotic species dominated. The higher ligand concentrations measured at the southern station are probably related to higher algal numbers at this site. Because ligand concentrations were higher, inorganic cobalt concentrations (Co′) south of the APF are extremely low, at femtomolar levels, whereas north of the APF calculated Co′ are much higher at picomolar levels where ligand concentrations were lower.
Extra keywords: ligands, speciation.
Acknowledgments
This research was funded by grants from NERC (PRIME) and the EU (MERLIM No. MAS3-CT95–0005). Samples were collected during a cruise with the German research vessel Polarstern (ANT XVI/3); assistance with the collection by officers and crew, and fellow scientists on board of the Polarstern, is gratefully acknowledged. Finally, we thank Mak Saito and two anonymous referees for reviews that helped to improve the manuscript.
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