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 (5parts per thousand-15parts per thousand) multiple negative spikes of delta(13)C, separated in places by sharp reversals of up to 20parts per thousand. Large oscillations of delta(13)C(org) between -36parts per thousand and -15parts per thousand from mean values of similar to24 +/- 2 in India, similar to26 +/- 2 in Madagascar, and similar to23 +/- 2 in South Africa occur before and after the P-T transition. The mean values are within the range of modern C3 plants (similar to-25parts per thousand). The negative delta(13)C(org) 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 delta(13)C can be explained by episodic release of methane from clathrates (similar to-60parts per thousand) either directly into the atmosphere or via the oceans, possibly during the disintegration of the southern continental shelf of Tethys. The rapid increases in delta(13)C may either signal aborted attempts of C4 plants (similar to-13parts per thousand) 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 delta(13)C 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.