Sea level variations during snowball Earth formation: 1. A preliminary analysis

A preliminary theoretical estimate of the extent to which the ocean surface could have fallen with respect to the continents during the snowball Earth events of the Late Neoproterozoic is made by solving the Sea Level Equation for a spherically symmetric Maxwell Earth. For a 720Ma (Sturtian) continental configuration, the ice sheet volume in a snowball state is similar to 750m sea level equivalent, but ocean surface lowering (relative to the original surface) is similar to 525m due to ocean floor rebounding. Because the land is depressed by ice sheets nonuniformly, the continental freeboard (which may be recorded in the sedimentary record) at the edge of the continents varies between 280 and 520m. For the 570Ma (Marinoan) continental configuration, ice volumes are similar to 1013m in eustatic sea level equivalent in a soft snowball event and similar to 1047m in a hard snowball event. For this more recent of the two major Neoproterozoic glaciations, the inferred freeboard generally ranges from 530 to 890m with most probable values around 620m. The thickness of the elastic lithosphere has more influence on the predicted freeboard values than does the viscosity of the mantle, but the influence is still small (similar to 20m). We therefore find that the expected continental freeboard during a snowball Earth event is broadly consistent with expectations (similar to 500m) based upon the inferences from Otavi Group sediments.