Examining the relationship between temperature and δ18O of freshwater molluscan carbonate from modern and Pleistocene fluvial sediments from the British Isles

The δ18O of freshwater molluscan carbonate (δ18Oc) from fluvial sequences has the potential to be a key palaeoclimate archive, given the close association between δ18Oc values and temperature in temperate lowland freshwater systems. However, the scarcity of systematic modern and Pleistocene studies from these deposits has limited the use of molluscan carbonate δ18Oc as a proxy for climate change. Here we present a study of fluvial molluscan carbonate δ18Oc from modern river systems and Pleistocene fluvial sequences located in central and southeast Britain. We compare molluscan carbonate δ18Oc from four species of gastropod to independently-derived estimates of temperature from the same contexts. We demonstrate that the δ18Oc of modern shells from three sites in southeast Britain are consistent with formation under equilibrium conditions with modern water temperature and δ18Ow values, which are in turn controlled by prevailing air temperature. The relationship between the δ18Oc value and temperature is also observable in the data obtained from fossil shells from ten Pleistocene sequences. Despite uncertainties with the interpretation of both the δ18Oc and palaeotemperature data at several localities, and the paucity of mollusc shells from cold climate contexts, this study highlights the potential of using δ18Oc analysis to obtain palaeoclimatic records from long Pleistocene fluvial sequences in temperate regions.