Transport limitation of the silicate weathering negative feedback on global temperature: implications for the Neoproterozoic glaciations

One of the foundation ideas of earth system science is that there is a negative feedback on global temperatures that operates via the carbonate-silicate weathering cycle: Buildup of CO2 in the atmosphere leads to higher temperatures. These increases silicate weathering, that in turn removes more CO2. However, the supply of material for silicate weathering is itself limited by the tectonic cycle, and this limits the effectiveness of the negative feedback at high global temperatures. Here we show using a very simple model of the geological carbon cycle that this limitation can readily lead to long-period snowball-greenhouse oscillations, with intervals between extreme glaciations of order tens of millions of years. We suggest that this is the explanation of the series of very severe glaciations during the Neoproterozoic. Our simple model gives qualitatively consistent estimates of excursions in carbonate δ13C during this time period, and suggests a large flux of oxygen to the atmosphere, broadly consistent with data.