Fe(II) stability in seawater.

Hopwood, Mark J. , Santana-González, Carolina , Gallego-Urrea, Julian , Sanchez, Nicolas, Achterberg, Eric P. , Ardelan, Murat V., Gledhill, Martha, González-Dávila, Melchor, Hoffmann, Linn, Leiknes, Øystein, Santana-Casiano, Juana Magdalena , Tsagaraki, Tatiana M. and Turner, David (2018) Fe(II) stability in seawater. Open Access Biogeosciences Discussions . pp. 1-29. DOI 10.5194/bg-2018-439.

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Abstract

The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II). Here we deploy flow injection analysis to measure in-situ Fe(II) concentrations during a series of mesocosm/microcosm experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During 5 mesocosm/microcosm experiments in Svalbard and Patagonia, where dissolved (0.2µm) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24–65% of DFe suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were retarded relative to calculated constants derived from ambient temperature, salinity, pH and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations <2nM and attributed to a stabilising effect of cellular exudates upon Fe(II). This enhanced stability of Fe(II) under post-bloom conditions, and the existence of such a high fraction of DFe as Fe(II), challenges the assumption that DFe speciation is dominated by ligand bound-Fe(III) species.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/FP7/603773
Keywords: Iron, biogeochemistry, Fe(II), trace elements
Research affiliation: OceanRep > SFB 754 > B10
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > SFB 754
Refereed: No
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-2018-439
ISSN: 1810-6285
Projects: OCEAN-CERTAIN, SFB754, EACFe
Date Deposited: 29 Oct 2018 11:23
Last Modified: 29 Oct 2018 12:13
URI: http://oceanrep.geomar.de/id/eprint/44586

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