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Thursday, October 3, 2013

"Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum," by James D. Wright & Morgan F. Schaller, PNAS 110 (October 2013); doi: 10.1073/pnas.1309188110

Proceedings of the National Academy of Sciences, 110(40) (October 2013) 15908-15913; doi:

Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum

James D. Wright and Morgan F. Schaller


The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE’s onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ18O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ18O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ13C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of 13C-depleted carbon. During the CIE, a clear δ13C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ13C decreased by ∼20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC).

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