Evidence of taxonomic non-equilibrium effects in the clumped isotope composition of modern cephalopod carbonate

The stable oxygen isotope composition (δ18O) of ammonites and belemnites is a common proxy for Jurassic and Cretaceous sea temperatures. The challenges and uncertainties associated with cephalopod δ18O and other proxy based paleotemperature reconstructions make cephalopods such as ammonites and belemnites a favourable target for carbonate clumped isotope paleothermometry. Our measurements of the clumped isotopic composition of modern cephalopods (Nautilus pompilius, Nautilus macromphalus, Nautilus belauensis and Sepia officianalis), however, confirm significant “vital effects” in clumped isotopic of cephalopod aragonite.