A rapid rise of seawater δ13C during the deglaciation of the Marinoan Snowball Earth

Abstract

The Marinoan Snowball Earth glaciation (~650–635 Ma) was followed by an increase in atmospheric O2 level and the diversification of eukaryotes. These dramatic changes have been assumed to have resulted from the rapid recovery of primary productivity during deglaciation, but this hypothesis has not yet been tested. Carbonate carbon isotope (δ13Ccarb), closely related to organic matter production and burial, has the potential to provide with the most straightforward evidence for the perturbation in marine carbon cycle. However, individual δ13Ccarb record might be less well-suited to test this hypothesis than a large data compilation. Here, we analyze 1590 globally-distributed carbonate carbon isotope data from the Marinoan cap carbonate. The least square sum analysis of the shallow-water cap carbonate δ13Ccarb data indicates that the carbon isotopic composition of seawater dissolved inorganic carbon (DIC, δ13CDIC) was −3.01‰ during cap carbonate precipitation. This result sharply contrasts with the assumed synglacial seawater δ13CDIC value of −5‰, which was verified with a binary mixing model. The 2‰ increase in the seawater δ13CDIC can be attributed to intensive organic matter production and burial during the deglaciation in less than 106 years. Massive organic carbon burial in the wake of the Marinoan Snowball Earth glaciation contributed a postglacial increase of atmospheric O2 level by 3.8% to 13.4% PAL (present atmospheric level) and thus further facilitated diversification of eukaryotes.