Distinct iron cycling in a Southern Ocean eddy

• Published in: Nature Communications
• Main Authors: Ellwood, Michael J., Strzepek, Robert F., Strutton, Peter G., Trull, Thomas W., Fourquez, Marion, Boyd, Philip W.
• Other Authors: Department of Education and Training | Australian Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2020
• Subjects: General Physics and Astronomy; General Biochemistry, Genetics and Molecular Biology; General Chemistry; Southern Ocean
• Online Access: http://dx.doi.org/10.1038/s41467-020-14464-0; http://www.nature.com/articles/s41467-020-14464-0.pdf; http://www.nature.com/articles/s41467-020-14464-0

Abstract Mesoscale eddies are ubiquitous in the iron-limited Southern Ocean, controlling ocean-atmosphere exchange processes, however their influence on phytoplankton productivity remains unknown. Here we probed the biogeochemical cycling of iron (Fe) in a cold-core eddy. In-eddy surface dissolved Fe (dFe) concentrations and phytoplankton productivity were exceedingly low relative to external waters. In-eddy phytoplankton Fe-to-carbon uptake ratios were elevated 2–6 fold, indicating upregulated intracellular Fe acquisition resulting in a dFe residence time of ~1 day. Heavy dFe isotope values were measured for in-eddy surface waters highlighting extensive trafficking of dFe by cells. Below the euphotic zone, dFe isotope values were lighter and coincident with peaks in recycled nutrients and cell abundance, indicating enhanced microbially-mediated Fe recycling. Our measurements show that the isolated nature of Southern Ocean eddies can produce distinctly different Fe biogeochemistry compared to surrounding waters with cells upregulating iron uptake and using recycling processes to sustain themselves.