A rapid rise of seawater δ~(13)C during the deglaciation of the Marinoan Snowball Earth

摘要

The Marinoan Snowball Earth glaciation (similar to 650-635 Ma) was followed by an increase in atmospheric O-2 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 (delta C-13(carb)), 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 delta C-13(carb) 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 delta C-13(carb) data indicates that the carbon isotopic composition of seawater dissolved inorganic carbon (DIC, delta C-13(DIC)) was -3.01 parts per thousand during cap carbonate precipitation. This result sharply contrasts with the assumed synglacial seawater delta C-13(carb) value of -5 parts per thousand, which was verified with a binary mixing model. The parts per thousand increase in the seawater delta(13)Crqc can be attributed to intensive organic matter production and burial during the deglaciation in less than 10(6) years. Massive organic carbon burial in the wake of the Marinoan Snowball Earth glaciation contributed a postglacial increase of atmospheric O-2 level by 3.8% to 13.4% PAL (present atmospheric level) and thus further facilitated diversification of eukaryotes.