Abstract

Understanding the oceanic phosphate concentration is critical for understanding marine productivity and oxygen evolutions throughout Earth history. During the Archean, estimates of marine phosphate levels range from depleted to enriched conditions. However, biogeochemical conditions required for sustaining high phosphate concentrations while retaining an anoxic atmosphere during the Archean remain ambiguous. Here, we employ a biogeochemical model of the marine phosphate cycle to determine the conditions under which oceanic phosphate levels could have been higher than present-day values during the Archean after the emergence of oxygenic photoautotrophs. We show that, under the presence of oxygenic photoautotrophs, phosphate-rich oceans require the limitation by factors other than phosphate, or a combination of ocean stagnation and a high outgassing rate of reducing gases. If these conditions were not met, the occurrence of oceanic phosphate levels higher than present-day values during the Archean would require the absence of oxygenic photoautotrophs.