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 O-2 and Fe II. The oxidation rate depends on the oceanic pH profile, which is calculated as a function of the atmospheric CO2 pressure. In this first part, the 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 varied between 10(-10) and 10(-6) mol kg(-1). It is shown that this Fe II oxidation by O-2 is very efficient and that relatively low O-2 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.