Isotopic analysis of coexisting Late Jurassic fish otoliths and molluscs: Implications for upper-ocean water temperature estimates

Abstract

The δ¹⁸O compositions of well-preserved Jurassic fish otoliths from Wootton Bassett, UK, provide upper-ocean paleotemperatures that are comparable with those derived from the isotopic analysis of fish tooth phosphates, providing independent scrutiny of such paleotemperatures. δ¹⁸O otolith temperatures in excess of 30 °C also rival temperatures associated with the middle Cretaceous thermal maximum. The negative carbon isotopes of the otoliths may point to a freshwater influence and potentially migratory nature of the fish. However, given the large departures from equilibrium fractionation toward more negative carbon values reported from modern marine fish, we consider our temperature interpretations to be robust and representative of the marine depositional environment. Depleted δ¹³C values, we believe, suggest that the otoliths examined in this study belong to fish with high metabolic rates.