Large areas of the oceans were reducing during much of the Precambiran  (4.5 to 0.5 Ga). The Great Oxidation Event (GOE; 2.45-2.2 Ga )  most likely was associated with the establishment of a redox-cline at the base of the surface mixed layer of the ocean.  In the modern ocean, the bottom of the mixed layer often lies above the base of the photic zone . Thus, an ecosystem model for the Precambrian should reflect the net primary production (NPP) of oxygenic phototrophs in the mixed layer and anoxygenic phototrophs below (NPP_ox and NPP_red, respectively). Satelite data and a vertically generalized production model (VGPM) can be used to calculate the mixed layer NPP relative to the NPP below. We use this to estimate the potential role of NPP_red below the mixed layer. The model implies that ~34% of the Precambrian total NPP would have been NPP_red if factors such as climate were comperable to today. High rates of exported NPP_red are consistent with the Precambrian sulfur isotope record which suggests that high rates of sulfate reduction proceeded the GOE.

 

Figure: Results of the model of anoxigenic photosynthesis. Percent is relative to total production.