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

Whitby, Hannah ORCID: 0000-0002-0064-3052, Planquette, Helene, Cassar, Nicolas, Bucciarelli, Eva, Osburn, Christopher L, Janssen, David J, Cullen, Jay T, Gonzalez, Aridane G, Voelker, Christoph and Sarthou, Geraldine
(2020) A call for refining the role of humic-like substances in the oceanic iron cycle. SCIENTIFIC REPORTS, 10.

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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.

Item Type: Article
Uncontrolled Keywords: biogeochemsitry, environmental chemistry, marine chemistry
Depositing User: Symplectic Admin
Date Deposited: 15 Apr 2020 10:01
Last Modified: 20 Jul 2022 13:10
DOI: 10.1038/s41598-020-62266-7
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3083209