Somes, C. J., Dale, A. W., Wallmann, K., Scholz, F., Yao, W., Oschlies, A., Muglia, J., Schmittner, A., & Achterberg, E. P. (2021). Constraining Global Marine Iron Sources and Ligand-Mediated Scavenging Fluxes With GEOTRACES Dissolved Iron Measurements in an Ocean Biogeochemical Model. Global Biogeochemical Cycles, 35(8), e2021GB006948. https://doi.org/10.1029/2021GB006948
Iron is a key, bio essential micronutrient controlling phytoplankton growth in vast regions of the global ocean. Despite its importance, uncertainties remain high regarding external iron source fluxes and internal marine cycling on a global scale, including removal (scavenging) rates and mechanisms. Iron concentrations in the ocean are affected not only by the source fluxes but also by the presence of ligands, compounds that maintain iron in a dissolved form (more bioavailable) and counteract removal mechanisms (transferring dissolved iron to particulate, less bioavailable form). In this study, the authors used a global dissolved iron (Fe) data set, including GEOTRACES measurements, to constrain source and scavenging fluxes in the marine iron component of a global ocean biogeochemical numerical model. The variable ligand parameterization improved the global model-data misfit the most, suggesting that bacteria are an important source of ligands to the ocean. Further parameterization of atmospheric deposition and release of iron from sediments further improved the model most notably in the surface ocean. High scavenging rates were then required to maintain the iron inventory. The model simulates a tight spatial coupling between source inputs and scavenging rates, which may be too strong due to underrepresented ligands near source inputs, contributing to large uncertainties when constraining individual fluxes with dissolved iron concentrations. Model biases remain high and are discussed to help improve global marine iron cycle models.