The main component of this data set comprises calculated inorganic iron concentrations (Fe' = sum of iron hydroxide species). Inorganic iron is the most bioavailable chemical form of Fe in the ocean. Concentrations of Fe' were calculated according to two models, which we refer to as the discrete ligand model and the continuous binding site model. The discrete ligand model, which is currently applied to calculate Fe speciation in global biogeochemical models, combines dissolved Fe concentrations, conditional stability constants and ligand concentrations to obtain inorganic iron, whilst the continuous distribution model uses the NICA-Donnan model to obtain Fe'.