Calcium isotope constraints on the end-Permian mass extinction

The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (delta C-13) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (delta(44)/Ca-40) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report delta(44)/Ca-40 across the Permian-Triassic boundary from marine limestone in south China. The delta(44)/Ca-40 exhibits a transient negative excursion of similar to 0.3 parts per thousand over a few hundred thousand years or less, which we interpret to reflect a change in the global delta(44)/Ca-40 composition of seawater. CO2-driven ocean acidification best explains the coincidence of the delta(44)/Ca-40 excursion with negative excursions in the delta C-13 of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average delta C-13 of CO2 released was heavier than -28 parts per thousand and more likely near -15 parts per thousand; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction.