Evidence for end-Permian ocean acidification from calcium isotopes in biogenic apatite

C record of carbonate rocks (δ 13 C carb ), for the selective extinction of heavily calcifi ed marine animals, and for the abrupt transition in carbonate facies across the extinction horizon, an additional proxy is necessary to distinguish among these options. Calcium isotopes hold promise for differentiating between suggested scenarios for change in seawater carbonate chemistry linked with the end-Permian extinction. The calcium cycle is linked to the carbon cycle through the weathering of limestone and the deposition of calcium carbonate sediments. Calcium isotopes fractionate by ~0.6‰ and ~1.3‰ in calcite and aragonite, respectively, during the precipitation of modern carbonate minerals, meaning carbonate sediments are enriched in the lighter isotope relative to the seawater from which they precipitated (Skulan et al., 1997; Tang et al., 2008). Imbalances between calcium delivery and burial fl uxes and changes in the magnitude of fractionation during carbonate deposition will result in changes in the δ 44/40 Ca of seawater and will be recorded in marine sediments (DePaolo, 2004; Farkao et al., 2007). Therefore, variation in the δ