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

Journal Article (Journal Article)

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.

Full Text

Duke Authors

Cited Authors

  • Whitby, H; Planquette, H; Cassar, N; Bucciarelli, E; Osburn, CL; Janssen, DJ; Cullen, JT; González, AG; Völker, C; Sarthou, G

Published Date

  • April 9, 2020

Published In

Volume / Issue

  • 10 / 1

Start / End Page

  • 6144 -

PubMed ID

  • 32273548

Pubmed Central ID

  • PMC7145848

Electronic International Standard Serial Number (EISSN)

  • 2045-2322

International Standard Serial Number (ISSN)

  • 2045-2322

Digital Object Identifier (DOI)

  • 10.1038/s41598-020-62266-7

Language

  • eng