Fe (III) speciation in the high nutrient, low chlorophyll Pacific region of the Southern Ocean

• Published in: Marine Chemistry
• Main Authors: Nolting, R.F., Gerringa, L.J.A., Swagerman, M.J.W., Timmermans, K.R., Baar, H.J.W. de
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1998
• Subjects: Seawater; Southern Ocean; Chemical speciation; Iron; Pacific
• Online Access: https://hdl.handle.net/11370/b14bce99-9130-48dd-97de-fb6289427e5a; https://research.rug.nl/en/publications/b14bce99-9130-48dd-97de-fb6289427e5a; https://doi.org/10.1016/S0304-4203(98)00046-2; https://pure.rug.nl/ws/files/14544192/1998MarChemNolting.pdf

Fe speciation was measured with competitive ligand equilibration adsorptive cathodic stripping voltammetry in the Pacific part of the Southern Ocean between 58° and 68°30′S along the 90°W meridian. The conditional stability constant (K′ with respect to [Fe3+]) was between 10^20.6 and 10^21.6 when one organic ligand was detected. The ligand concentration ([Lt]) varied between 2.2 and 12.3 equivalents of nM Fe (nEq of Fe). The ligand concentration was at least 6 times, and generally more than 10 times, that of the total dissolvable Fe concentration. At one station a depth profile was sampled where below 200 m depth, two organic ligands were measured with K1′=10^21 and K2′=10^22.4. Organic complexation of Fe was similar to results found elsewhere judging from the overall organic alpha value (K′*[Lt]) 10^12.4–10^13.9. The lower values of organic alpha were within one order of magnitude of our choice of the inorganic alpha (10^11.9) in which case the organic and inorganic ligands could compete effectively for Fe. Different values of organic alpha and the occurrence of two organic ligand classes were consistent with differences in hydrography. South of the Polar Front, the least organic complexation occurred (organic alpha=10^12.4, organic complexation around 80%), where the highest chlorophyll a concentrations were measured.