Ligand-Iron Dynamics and their Influence on Dissolved Iron Distributions in a Global Model

Dissolved iron is a key limiting nutrient over ~1/3 of the oceans. Distributions of dissolved iron and iron residence times are thought to be strongly influenced by iron-binding ligands. In this study, we will present results from global-scale, ocean biogeochemical simulations with three different approaches to modeling the iron ligand interactions. We simulate these dynamics with an implicit ligand model, an explicit ligand model with a globally constant ligand concentration, and an explicit ligand model with dynamic sources and sinks. The source for iron-binding ligands in our dynamic model is remineralization of POM, and the sinks include implicit degradation by bacteria, photochemical degradation, and aggregation and particle scavenging of the ligands. In our model, iron-binding ligands influence dissolved iron distributions through their modulation of iron scavenging rates, which is a function of the sinking particle flux. Our goal is to understand how implementations of ligand cycling processes influence iron-binding ligand and dissolved iron distributions, and to gain a better understanding of ligand-iron interactions in the real ocean through comparisons of model output with observations of both iron-binding ligands and dissolved iron concentrations.