How Fast was the Onset of the Paleocene-Eocene Thermal Maximum? Was a Comet to Blame?!?!

A Comet Caused the PETM!

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

Authors:

Wright et al

Abstract:

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).

No! It Did NOT!

Onset of carbon isotope excursion at the Paleocene-Eocene thermal maximum took millennia, not 13 years

Authors:

Zeebee et al

Abstract:

The Paleocene-Eocene thermal maximum (PETM) may represent the best paleo-analog for rapid and massive carbon release to the ocean and atmosphere. Thus, constraining the carbon release rate at its onset is critical. Wright and Schaller (1) use records from apparently rhythmically layered shelf sediments to argue that the layering is annual and that the onset of the carbon isotope excursion (CIE, fingerprint for carbon release) in the surface ocean was complete in 13 y. Using basic carbon cycle and climate considerations, we show this is not feasible. In fact, Wright and Schaller’s isotope records indicate that the CIE onset took at least several millennia. This finding rules out a cometary origin of the carbon release.

Yes, it did!

Reply to Pearson and Nicholas, Stassen et al., and Zeebe et al.: Teasing out the missing piece of the PETM puzzle

Authors:

Wright et al

Abstract:

Understanding the Paleocene-Eocene Thermal Maximum (PETM) critically depends on knowing the rate at which the perturbation carbon was released. In our report (1) we argue that the layered Marlboro Clay may provide this important constraint. Our strongest evidence in support of the rapid release of carbon at the onset of the PETM is the differential response of the %CaCO3 and δ13C in the Millville core. The sharp %CaCO3 decrease occurred over 4 mm, compared with the δ13C decrease over an interval of 25 cm (figure 3 in ref. 1). Temporal differences are predicted by a rapid (instantaneous) release of light carbon, which would lower the surface ocean Graphic in a matter of months, in contrast to the carbon isotopic equilibrium exchange, which occurs on the scale of a decade (2) and can only be recorded in a core with a high sedimentation rates (1). Based on the rhythmic bedding in the Marlboro Clay, we argue that the drop in %CaCO3 occurred in less than a year and the δ13C equilibrium was on the order of a decade.

My guess is probably not given all we know of the PETM.