OCEAN ACIDIFICATION, VOLCANISM AND END-PERMIAN EXTINCTION: PERSPECTIVES BASED ON INTERPRETING CARBON ISOTOPE EXCURSIONS
As expected, the extent of perturbation to the saturation state and pCO2 depends on the magnitude and rate of carbon addition, which in turn is dependent on the presumed isotopic composition of the source CO2 and the duration and magnitude of the carbon isotope shift. An additional uncertainty to which the model is sensitive is the buffering capacity of the Late Permian ocean (before the perturbation), likely reduced from that of the modern ocean because of the presumed lack of deep-sea sedimentary CaCO3 (i.e., a very shallow CaCO3 compensation depth). In only the most extreme cases of a purely magmatic source of CO2 does the surface ocean become widely undersaturated with respect to CaCO3. Sources such as volatilization of organic-C rich sedimentary rocks, thermogenic methane production, or release of biogenic methane from clathrates drive smaller reductions in saturation state and increases in pCO2. The simulation that best matches the independent estimates of the degree of warming and quantity of CO2 released leads to moderate reductions in saturation state but substantial increases in pCO2of 20 ka duration, potentially sufficient to cause hypercapnia.