Organic iron(iii) speciation in surface transects across a frontal zone: the Chatham Rise, New Zealand
Feng Tian A C , Russell D. Frew A , Sylvia Sander A , Keith A. Hunter A and Michael J. Ellwood BA Department of Chemistry, University of Otago, Dunedin, New Zealand.
B National Institute of Water and Atmosphere, Hillcrest, Hamilton, New Zealand.
C Corresponding author. Email: ftian@alkali.otago.ac.nz
Marine and Freshwater Research 57(5) 533-544 https://doi.org/10.1071/MF05209
Submitted: 20 October 2005 Accepted: 5 May 2006 Published: 13 July 2006
Abstract
Iron (Fe) is a critical nutrient in marine systems and the organic complexation of Fe is a central factor of the marine biogeochemistry of Fe. In the present study, total dissolved Fe and its organic speciation were measured in filtered seawater samples (<0.2 μm) collected along three surface transects across the subtropical (ST) front, east of New Zealand, in austral spring (October 2000). Total dissolved Fe concentrations were low (~0.1 nm) in the subantarctic (SA) waters. The highest Fe concentration (~0.8 nm) was observed at the mixing boundary north of the Subtropical Convergence (STC) and then decreased relatively quickly both southward and northward. Cathodic stripping voltammetry was used to determine Fe speciation. The dissolved Fe(iii) was fully complexed (>99.9%) by natural organic ligands, which were found to occur in excess of the dissolved Fe concentration at 1.29 ± 0.33 nm (equivalent to an excess over Fe of ~1.0 nm), and with a complex stability of K′FeL,Fe3+ = 22.67 ± 0.22. The total ligand concentrations were consistently higher (~0.5 nm) in the ST and STC waters than in the SA waters. Our Fe data imply that the regional currents may be an important vehicle for transporting the elevated Fe across the front.
Extra keywords: organic speciation, subtropical front.
Acknowledgments
Samples for this study were collected during Cruise TAN0010 as part of NIWA’s Ocean Ecosystems Programme (C01X0027). We thank Stu Pickmere, Scott Nodder and Philip Sutton for the nutrient and hydrographic data. We wish to thank Robert Strzepek and two anonymous reviewers for their helpful comments. We also acknowledge financial support for F.T. from the Chemistry Department.
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