Clumped isotope thermometry applied to bivalve mollusks

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Shells of bivalve mollusks from higher latitudes are high-potential recorders of environmental variability on seasonal to decadal time-scales. However, temperature estimates based on common oxygen isotope determinations (i.e. (18O-values) of shell carbonate suffer from the weakness that the exact oxygen isotopic composition of the seawater is unknown in most cases. Clumped isotope measurements on CO2 released from marine carbonates by acid digestion have been demonstrated to function as a new powerful paleothermometer, because the deviation between measured and stochastic mass 47/44 isotopologue distributions (as expressed by (47-values) is independent of the oxygen isotopic composition of the ambient water and exclusively controlled by temperature, given that the carbonates grew in equilibrium with the ambient water. We request funding for the installation of the clumped isotope technique for mass 47 measurements in CO2. In a next step, we will study the temperature – (47 relationship for CO2 extracted from calcitic and aragonitic mollusks. Finally, combined (47 and (18O measurements will be performed on shells of the long-lived A. islandica and the fast-growing M. edulis to reconstruct seasonal variations in temperature and freshwater input throughout selected time intervals of the Holocene (Allerød, Medieval Cimate Optimum, Little Ice Age).