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.