Coupled carbon and silica cycle perturbations during the Marinoan snowball Earth deglaciation.

The snowball Earth hypothesis proposes that if polar ice sheets were to advance equatorward of a mid-latitude threshold, runaway ice-albedo effects would lead to a stable, globally ice-covered climate state that would require extremely high atmospheric pCO2 levels (supplied by volcanic degassing over millions of years) for deglaciation. Geologic evidence, including globally distributed and low-latitude glacial deposits, suggests that two such global glaciations occurred during the Neoproterozoic. We model the coupled carbon and silica cycles through a snowball Earth event, including the extremely high pCO2 and dramatically accelerated chemical weathering of its aftermath. The enhanced delivery of dissolved weathering products to the ocean induces elevated sedimentary burial of CaCO3 (deposited as "cap carbonates") and SiO2. Uncertainty in the relative importance of carbonate versus silicate weathering allows a wide range of possible CaCO3 burial magnitude, potentially dwarfing that of SiO2. However, total SiO2 burial is insensitive to weathering strengths, and is set by the amount of CO2 required for deglaciation (~1019 mol). Chert associated with Marinoan post-glacial cap carbonates in Africa and Mongolia corroborate modeled predictions of elevated SiO2 burial. [ABSTRACT FROM AUTHOR]