The start of the Ediacaran period is defined by one of the most severe climate change events recorded in Earth history—the recovery from the Marinoan ‘snowball’ ice age, ∼635 Myr ago (ref. 1). Marinoan glacial-marine deposits occur at equatorial palaeolatitudes2, and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about -5 and +15 parts per thousand, respectively3,4,5; these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1,3,4. This abrupt transition records a climate system in profound disequilibrium3,6 and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating Phanerozoic deglaciation. Hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3, deep-ocean out-gassing during post-glacial oceanic overturn7 or methane hydrate destabilization8,9,10. Here we report the broadest range of oxygen isotope values yet measured in marine sediments (-25‰ to +12‰) in methane seeps in Marinoan deglacial sediments underlying the cap carbonate. This range of values is likely to be the result of mixing between ice-sheet-derived meteoric waters and clathrate-derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater. The equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day. A pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions, abrupt unidirectional warming, cap carbonate deposition, and a marine oxygen crisis. Our findings suggest that methane released from low-latitude permafrost clathrates therefore acted as a trigger and/or strong positive feedback for deglaciation and warming. Methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11,12,13 that coincides with critical boundaries in the geological record14,15 and may represent one particularly important mechanism active during conditions of strong climate forcing.
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We thank the NSF and NASA Exobiology for funding, A. Derkowski and T. Bristow for assistance with clay mineralogy, D. Winter for replicate isotopic analyses and I. Fairchild for a review.
Author Contributions M.J.K. collected samples and wrote the manuscript; D.D.M. collected samples, performed geochemical analyses and wrote the supplemental section; C.v.d.B. collected samples. All authors discussed the results and commented on the manuscript.
The file contains Supplementary Figure S1, Supplementary Tables S1-S2 and Supplementary Discussion. Figure S1 shows Reynella Siltstone XRD traces supporting the presence of smectite. Tables S1 & S2 provide isotopic data for Fig. 2 and quantitative mineralogy of Reynella Siltstone. Discussion text outlines probable isotopic and chemical effects of clathrate destabilization.