Fig. 3.
Time-dependent model scenario (#2) of snowball initiation. (A) Prescribed carbon fluxes, due to oxygenic production (Fprod), aerobic remineralization (Fremin,O2), input from volcanoes and carbonate weathering (Fin, multiplied by 23), sulfate remineralization (Fremin,SO4) and iron reduction (Fremin,Fe). (*) The last two fluxes, representing anaerobic remineralization, are plotted shifted and their initial value before the anomaly is zero. (B) Carbonate speciation. (C) Organic and inorganic carbon masses (solid lines) and δ13C isotopic composition (dash). (D) Decrease in sulfate concentration [ΔSO4(T), blue], or, alternatively, the required sulfate flux into the ocean (green, solid) for the sulfate reduction scenario. The present-day riverine flux is shown by the green, dashed line. (E) Implied iron fluxes of Fe3+ for iron reduction part of the scenario (red, with present-day flux into the ocean shown in red dashed line), and the implied flux of Fe2+ for the sulfate reduction and pyrite formation (blue). (F) Organic and inorganic burial rates. (G) Ca2+ and the weathering fraction αwthr (SI Appendix). (H) Organic burial fraction f and non-steady-state fraction fδ defined in the text. (I) Atmospheric CO2 and ocean pH.