Multiple Organic Carbon Isotope Reversals across the Permo‐Triassic Boundary of Terrestrial Gondwana Sequences: Clues to Extinction Patterns and Delayed Ecosystem Recovery

Organic materials across the palynologically defined Permian‐Triassic (P‐T) boundary from five major terrestrial basins in the interior of the former Gondwana Supercontinent show large to very large (5‰–15‰) multiple negative spikes of δ13C, separated in places by sharp reversals of up to 20‰. Large oscillations of δ13Corg between −36‰ and −15‰ from mean values of ∼$$24\pm 2$$ in India, ∼$$26\pm 2$$ in Madagascar, and ∼$$23\pm 2$$ in South Africa occur before and after the P‐T transition. The mean values are within the range of modern C3 plants (∼−25‰). The negative δ13Corg spikes of the terrestrial plant remains complement similar spikes of smaller amplitude recorded globally in marine carbonates across the P‐T boundary. Sensitivity analyses of carbon fluxes in a coupled atmosphere‐ocean system indicate that the sharp declines in terrestrial and marine δ13C can be explained by episodic release of methane from clathrates (∼−60‰) either directly into the atmosphere or via the oceans, possibly during the disintegration of the southern continental shelf of Tethys. The rapid increases in δ13C may either signal aborted attempts of C4 plants (∼−13‰) to establish themselves at the expense of C3 plants or, more likely, reflect a punctuated increase in C3 biomass production related to elevated atmospheric CO2. Detection of a gradual negative trend in the Upper Permian and a similar positive recovery in the Lower Triassic, separated by up to three large negative δ13C spikes across the P‐T boundary in at least four terrestrial sections, caution against models of the end‐Paleozoic biodiversity collapse and ensuing Mesozoic recovery based on a singular perturbation at the P‐T boundary. Rather, these transitions may reflect multiple ecosystem stability states and abrupt responses during gradual forcing of a complex nonlinear system with thresholds.