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Influence of organic complexation on dissolved iron distribution in East Antarctic pack ice

journal contribution
posted on 2023-05-19, 18:16 authored by Genovese, C, Grotti, M, Pittaluga, J, Ardini, F, Janssens, JP, Kathrin WuttigKathrin Wuttig, Sebastien MoreauSebastien Moreau, Delphine LannuzelDelphine Lannuzel
Since Antarctic sea ice covers an area larger than the Antarctic continent itself, the discovery that it can fertilize the Southern Ocean with iron (Fe) has fostered a new breadth of research in recent years. In order to test the hypothesis that Fe-binding organic ligands control the distribution of dissolved iron (DFe) in Antarctic pack ice, iron organic speciation was investigated in samples collected during the Sea Ice Physics and Ecosystem eXperiment-2 (SIPEX-2) voyage in Austral winter/spring 2012. Dissolved Fe was measured using sector field inductively coupled plasma mass spectrometry, and iron organic speciation parameters were determined by competitive ligand equilibration - adsorptive cathodic stripping voltammetry method, using 1-nitroso-2-naphthol (NN) as the added ligand. The concentration of Fe-binding organic ligands (Lt) ranged from 4.9 nM to 41 nM (average of 14.9 ± 8.4 nM, n = 34), and was always higher than the corresponding DFe (average of 7.5 ± 4.5 nM, n = 34). Conditional stability constants (log K′Fe’L = 11.7–13.0) were similar to those previously observed in land-fast ice. Concentrations of DFe and Lt displayed similar depth profiles; their strong correlation (Spearman's ρ = 0.80, p < 0.001) suggested that Fe-binding organic ligands control DFe distribution in Antarctic pack ice. Unlike results previously obtained for land-fast ice, Fe-binding organic ligands in pack ice were never saturated with iron (Lt/DFe > 1). Estimates showed that pack ice would have released 0.45 μmol/m2/d of Lt during spring melt, 0.21 μmol/m2/d of which are free from Fe binding, and hence available for further complexation. Therefore, it is suggested that this excess of Fe-free ligands may play a key role in controlling the solubility of free or newly formed Fe in surface waters before the peak of primary production, outcompeting the Fe-binding organic ligands already present in seawater.

Funding

Department of Environment and Energy (Cwth)

History

Publication title

Marine Chemistry

Volume

203

Pagination

28-37

ISSN

0304-4203

Department/School

Institute for Marine and Antarctic Studies

Publisher

Elsevier Science Bv

Place of publication

Po Box 211, Amsterdam, Netherlands, 1000 Ae

Rights statement

© 2018 Elsevier B.V. All rights reserved.

Repository Status

  • Restricted

Socio-economic Objectives

Other environmental management not elsewhere classified

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