Challenging results on iron bioavailability in the Southern Ocean

21 November 2023

Fourquez and co-authors (2023, see reference below) conducted dissolved iron (dFe) uptake experiments with Phaeocystis antarctica, in order to establish processes controlling the dFe bioavailability in natural samples of the Southern Ocean. They show that the degree of bioavailability varied regardless of in situ dFe concentration and depth. This first result challenges the consensus that sole dFe concentrations can be used to predict Fe uptake in modeling studies. In addition, the range of this degree of bioavailability is wider than previously thought (<1 to ~200% compared to free inorganic Fe’). The authors also propose to couple dataset of Fe-binding ligands, dFe bioavailability, and δ⁵⁶Fe. Contrasting again with previous assumptions, they observe a negative correlation between dissolved δ⁵⁶Fe and total ligand concentrations, which might suggest against a role for complexation in driving dissolved δ⁵⁶Fe toward higher values.

**Figure:** This study investigates factors influencing the availability of a type of iron, dFe. In part (A), a table shows relationships between different iron forms, dFe availability, and iron uptake. Colours indicate the strength of connections, and stars mark significant relationships (P values smaller than 0.05). Part (B) uses PCA to explore correlations between iron uptake, chemistry, and ligands. The blue arrows represent key influences. The first two factors explain 36.55% and 24.13% of observed differences. We confirmed data normality with the Henze-Zirkler test.

Reference:

Fourquez, M., Janssen, D. J., Conway, T. M., Cabanes, D., Ellwood, M. J., Sieber, M., Trimborn, S., & Hassler, C. (2023). Chasing iron bioavailability in the Southern Ocean: Insights from Phaeocystis antarctica and iron speciation. Science Advances, 9. Access the paper: https://doi.org/10.1126/sciadv.adf9696

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