Redox Dynamics of the Atmosphere and Oceans Induced by the Paleoproterozoic Snowball Earth Events

The Paleoproterozoic Earth underwent profound environmental changes, including multiple severe glaciations and fluctuations in atmospheric oxygen (O₂) levels. However, the precise relationship between O₂ evolution and the glaciations remains unclear. Here, we use a biogeochemical cycle model involving carbon, phosphorus, sulfur, and oxygen to investigate the redox dynamics of the ocean-atmosphere system following the climatic transition to a super-greenhouse state after deglaciation. Our stochastic analysis reveals that climatic recovery on a timescale of ~10⁵ years from elevated atmospheric CO₂ levels (> 0.2 atm) triggers an extensive oxidation of the atmosphere and oceans over the subsequent 10⁶-10⁷ years, aligning with the large sulfur isotope anomaly in buried pyrite after the third Paleoproterozoic glaciation (~2.3 Ga). This finding suggests that the third glaciation represented an extensively glaciated, snowball state, which would have required massive accumulation of atmospheric CO₂ for deglaciation. Variation in the boundary conditions regarding the global redox budget, as represented by high reductant fluxes, may explain the return of atmospheric O₂ to Archean-like levels following the first (Makganyene) glaciation, which is also considered a snowball Earth.