Seafloor weathering can explain the disparate durations of Snowball glaciations

Abstract The Cryogenian Period (720–635 Ma) witnessed two Snowball Earth glaciations: the largest known perturbations to the geologic carbon cycle in Earth history. These two runaway ice-albedo catastrophes naturally test planetary climate stability and habitability. Geochronological data show that the Sturtian glaciation lasted 56 m.y., and the Marinoan was as short as 4 m.y., which is an unexplained difference previously attributed to changing volcanic outgassing rates and dust or ice albedo. Here, we propose that this difference in duration is instead due to changes in the extent of seafloor weathering, which was elevated during both glaciations by an acidic ocean under relatively high CO2. By assuming modern volcanic outgassing rates and a conservative range of ice albedos, we find that seafloor weathering rates 25–53 times higher than modern are required to suppress atmospheric CO2 and maintain glaciation for a 56 m.y. Sturtian glaciation, whereas <15 times higher than modern are required for a 4 m.y. Marinoan glaciation. Rates were plausibly enhanced further by reduced deep-sea sedimentation and low marine sulfate, which would have prevented hydrothermal anhydrite production and created more porous, weatherable oceanic crust. Geochemical data indicate low marine sulfate (<2 mM) during the Sturtian, which rebounded for the Marinoan (up to ~30 mM), and can account for the different seafloor weathering rates required by our model. Thus, our results suggest seafloor weathering and evolving ocean redox chemistry are critical for determining the duration of Snowball Earth glaciations.