The apparent iron solubility calculated from ambient temperature, pH and dissolved organic carbon in the Atlantic and Pacific oceans

Iron (Fe) is an important limiting nutrient in the marine environment constraining primary production across much of the ocean due to its sparse solubility in seawater. Iron availability regulates the magnitude and dynamics of ocean primary productivity, and is dependent on Fe solubility and speciation in seawater which in turn are influenced by physico-chemical properties such as pH, temperature, dissolved organic material. In this study, the apparent iron solubility (SFe(III)app) is calculated in an oversaturated system by setting an input of dissolved Fe(III) to 10 nmol L-1, at ambient ocean pH, temperature and dissolved organic carbon concentrations. This will result in the precipitation of Fe hydroxide, as ferrihydrite assumed in our system. The SFe(III)app is defined as the sum of aqueous inorganic Fe(III) species and Fe(III) bound to DOM, formed at a free Fe (Fe3+) concentration equal to the limiting solubility of Fe hydroxide (Fe(OH)3(s)). We compared calculated apparent iron solubility to measured dissolved iron concentrations (dFe) from three GEOTRACES cruises in the Atlantic and Pacific oceans. I aim to build a comprehensive picture on Fe speciation and dFe inventory in the ambient oceanic water column, with further feedbacks on primary productivity.