A call for refining the role of humic-like substances in the oceanic iron cycle

Type Article
Date 2020-04
Language English
Author(s) Whitby Hannah9, 10, Planquette Helene1, Cassar Nicolas1, 2, Bucciarelli Eva10, Osburn Christopher L.3, Janssen David J.4, 5, Cullen Jay T.6, González Aridane G.1, 7, Völker Christoph8, Sarthou Geraldine1
Affiliation(s) 1 : CNRS, Univ Brest, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
2 : Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA
3 : Marine, Earth, and Atmospheric Sciences, NC State University, Raleigh, NC, 27695, USA
4 : Institute of Ocean Sciences, Fisheries and Oceans Canada, 9860 W Saanich Rd, Sidney, BC, V8L 5T5, Canada
5 : University of Bern, Institute of Geological Sciences & Oeschger Center for Climate Change Research, Baltzerstrasse 1-3 3012, Bern, Switzerland
6 : School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada
7 : Instituto de Oceanografía y Cambio Global, IOCAG. Universidad de Las Palmas de Gran Canaria, ULPGC, Parque Científico Tecnológico de Taliarte, 35214, Telde, Spain
8 : Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany
9 : University of Liverpool, Liverpool, UK
10 : CNRS, Univ Brest, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
Source Scientific Reports (2045-2322) (Springer Science and Business Media LLC), 2020-04 , Vol. 10 , N. 1 , P. 6144 (12p.)
DOI 10.1038/s41598-020-62266-7
WOS© Times Cited 36

Primary production by phytoplankton represents a major pathway whereby atmospheric CO2 is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner. Here we show iron co-varying with electroactive humic substances at multiple open ocean sites, with the ratio of iron to humics increasing with depth. Our results agree with humic ligands composing a large fraction of the iron-binding ligand pool throughout the water column. We demonstrate how maximum dissolved iron concentrations could be limited by the concentration and binding capacity of humic ligands, and provide a summary of the key processes that could influence these parameters. If this relationship is globally representative, humics could impose a concentration threshold that buffers the deep ocean iron inventory. This study highlights the dearth of humic data, and the immediate need to measure electroactive humics, dissolved iron and iron-binding ligands simultaneously from surface to depth, across different ocean basins.

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Whitby Hannah, Planquette Helene, Cassar Nicolas, Bucciarelli Eva, Osburn Christopher L., Janssen David J., Cullen Jay T., González Aridane G., Völker Christoph, Sarthou Geraldine (2020). A call for refining the role of humic-like substances in the oceanic iron cycle. Scientific Reports, 10(1), 6144 (12p.). Publisher's official version : https://doi.org/10.1038/s41598-020-62266-7 , Open Access version : https://archimer.ifremer.fr/doc/00622/73388/