Reducing Power of Ferrous Iron in the Archean Ocean, 1. Contribution of Photosynthetic Oxygen

A quantitative model of the Archean ocean is developed in order to estimate the oxidation
rate of dissolved ferrous iron, a key process for the deposition of banded iron formations. The
continuity equation including chemical reactions and vertical transport is solved for 0 2 and
Fe II. The oxidation rate depends on the oceanic pH profile, which ks calculated as a function of the
atmospheric CO pressure. In this first part, the2 oxidation due to the reaction with photosynthetic
oxygen is considered. The results are presented as a function of the oxygen concentration in the mixed layer which was varie_• between 10-10 and 10-6 mol kg . It ks shown that this Fe II oxidation by 0 is very efficient and that r•latively low 02 levels are required for the oxidation rate to
be limited by upward transport of iron to the surface ocean. Possible evolutionary paths for the Archean ocean-atmosphere system are discussed by an analysis of the balance of the iron input flux.