CA, MO AND U ISOTOPES EVIDENCE OCEAN ACIDIFICATION AND DEOXYGENATION DURING THE LATE PERMIAN MASS EXTINCTION

The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained.

Here we use Ca, Mo and U isotopes applied to globally distributed, well dated late Permian- early Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing d^44/40Ca compositions, paralleling a major decrease in d¹³C values. These findings support an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability during the early Triassic, which is similar to that of the early-middle Cambrian, suggests imply largely biogenetically controlled perturbations of the oceanic carbon cycle. These findings strengthen the evidence for a global ocean acidification event coupled with rapid expansion of anoxic zones as drivers of end-Permian extinction in the oceans.