Abstract
One of the most dramatic global warming events in the Earth’s history occurred at the Paleocene-Eocene boundary (ca. 55 Ma). During the Paleocene-Eocene thermal maximum (PETM), the global temperature increased by more than 4°C within a few thousand years, accompanied by an abrupt negative carbon isotope excursion (CIE) in both the marine and terrestrial environments. Although this excursion implies a massive and rapid addition of 13C-depleted carbon to the oceans and atmosphere, the source of the massive carbon injection during the PETM remains uncertain.
To provide some constraints on the cause of the PETM, we re-examined the observed magnitude of the CIE, and then reconstructed the perturbation of the global carbon cycle during the PETM, using a simple one-box global carbon-cycle model.
The eruption of the North Atlantic Igneous Province (NAIP) appears to be the most plausible candidate for a triggering mechanism of the PETM. Our model indicates that the CIE of –3‰ is best explained by inputs of 2,200 Gt-C of thermogenic methane, produced by NAIP volcanism, and 700–2,800 Gt-C of biogenic methane produced by the subsequent dissociation of seafloor gas hydrates within 10 kyr. The uncertainty in the mass of released biogenic methane is attributed mainly to high variability in atmospheric pCO2 reconstructed for the late Paleocene (ranging from <300 to >2,000 ppm). However, the global temperature rise calculated by our model is 1.4°C at most, and we cannot reconstruct a temperature anomaly exceeding 4°C.
