The on-going acidification of modern oceans is a major issue of concern because it may have serious consequences for the survival of shelly marine invertebrates as the 21st century progresses. This is driven by anthropogenic CO2 release and the additional consequence of global warming is predicted to produce ocean de-oxygenation within a century. A better understanding of such effects will come from study of past ocean acidification and anoxic events but this objective is hampered both by poor constraint of ancient pH and redox values. This study aims to develop a new stable isotope technique – using Ca isotope fluctuations – to monitor ocean carbonate budgets and to evaluate the S isotope record of the oceans, a system primarily affected by ocean redox and evaporite burial. This approach will be applied to the end-Permian catastrophe, the greatest mass extinction of all time, to evaluate the hypothesis that the marine biotic crisis was caused by acidification and anoxia. Comparisons will be drawn with the non-steady state oceans of the late Precambrian Snowball Earth world when similar perturbations in ocean chemistry produced similar rock types to those seen in the aftermath of the Permian extinction. This uniquely, multi-pronged geochemical approach will allow coupled box modelling of the marine Ca and S budget and thus for the first time it will be possible to relate changes in these systems to oceanic oxygenation and pH levels and the contemporaneous mass extinction.The multi-pronged geochemical approach of this research will ultimately help to better constrain the timing and future effects of the anthropogenic emissions of CO2 on ocean acidification, marine biologic activity and global biogeochemical cycles.