Fig. 6
From: Anoxygenic photosynthesis and the delayed oxygenation of Earth’s atmosphere
Representative results from our global ocean-sediment biogeochemical model (CANOPS-KB). a Each curve shows net oxygen fluxes (Φox) as a function of atmospheric pO2. Intersection points at Φox = 0 indicate regions of parameter space in which the O2 cycle is at equilibrium and dominated by negative feedback (negative slope) and positive feedback (positive slope). Circles plotted along the black curve thus show examples of stable (open) and unstable (closed) equilibrium points for model runs at a nominal deep ocean Fe/P ratio of 100. Each curve is labeled by an assumed external reductant flux (i.e., volcanic/metamorphic reductant input minus O2 accumulation due to hydrogen escape and/or imbalances in global S and Fe cycling, Φred) in Tmol O2 equivalents year−1. b Each curve plots stable equilibrium pO2 values as a function of deep ocean Fe/P ratio ([Fe/P]d) under the same conditions as shown in a. The (○) shows our nominal model ([Fe/P]d = 100 and no external reductant input). Arrows above and below the curves denote regions where our model predicts runaway oxygenation or deoxygenation, respectively. Also shown in b are approximate estimates of [Fe/P]d for the Archean and Proterozoic (shaded gray bars; see text)
