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

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 pCO(2). 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 delta O-18 cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for delta O-18 amplitudes and layer counts. High- resolution stable isotope records show 3.5% delta C-13 decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of C-13-depleted carbon. During the CIE, a clear delta C-13 gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric delta C-13 decreased by similar to 20%. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC).