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

• Published in: Marine Chemistry
• Main Authors: Genovese, C, Grotti, M, Pittaluga, J, Ardini, F, Janssens, J, Wuttig, K, Moreau, S, Lannuzel, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science Bv 2018
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Antarctic; Austral; Southern Ocean; The Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.1016/j.marchem.2018.04.005; http://ecite.utas.edu.au/126077

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′ FeL = 11.713.0) 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/m 2 /d of Lt during spring melt, 0.21 μmol/m 2 /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.