Methanogenic Blow-up in the End-Permian Carbon Cycle

The cause of the end-Permian extinction---arguably Earth's greatest
biological crisis, about 252 million years ago---remains mysterious.
We focus on concurrent disruptions in the global carbon cycle. By
transforming geochemical signals into physical fluxes, we reveal an
incipient singularity in the flux of CO2 into the oceans. Given
reports of pre-existing anoxia, we hypothesize that the anaerobic
degradation of abundant recalcitrant organic carbon provided the CO2
source, and that the evolution of a new microbial metabolic pathway
caused the blow-up. We show that the most probable date for the
emergence of the fast acetoclastic pathway in Methanosarcina,
responsible for most modern biogenic methane, ranges between 238-268
million years ago. Because methanogens are limited by nickel, we
hypothesize that increased nickel concentrations enhanced
Methanosarcina's growth. Our analyses of late-Permian South China
sediments show that nickel indeed increased sharply at the extinction,
probably as a consequence of concurrent Siberian volcanism.