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Are molluscs a reliable archive for stable isotope paleo-temperature reconstructions? Implications from dual clumped isotope thermometry

Shell carbonates of marine molluscs are a widely used archive for paleo-environmental reconstructions. However, their use for temperature reconstructions may be impeded by species-specific vital effects and/or a lack of knowledge of the chemical and isotopic composition of paleo-seawater. Clumped isotope (∆47) thermometry of marine carbonates enables temperature reconstructions independent of seawater composition provided the carbonate formed in thermodynamic equilibrium. Dual clumped isotope thermometry, i.e. simultaneous analysis of ∆48 alongside ∆47, offers the opportunity to determine if a carbonate formed in isotopic equilibrium and to account for kinetic effects taking place prior to and/or during precipitation. Here, we present dual clumped isotope data for several modern mollusc specimens (including bivalves and gastropods) with average growth temperatures ranging from 5-27°C. We find that most specimens analysed in this study exhibit dual clumped isotope compositions which are indistinguishable from equilibrium. Moreover, their ∆47-derived temperatures agree within errors with their growth temperatures. We interpret the apparent equilibrium calcification of mollusc shell carbonates to be a possible consequence of a relatively low pH at the site of calcification. The absence of any resolvable kinetic isotope effects makes molluscs a reliable archive for highly precise (95CI of <2.2°C) temperature reconstructions via ∆47-analysis. Based on previous ∆47 investigations of molluscs grown at known seawater oxygen isotope compositions (δ18OSW), we also determine the temperature dependencies of the oxygen isotope fractionation between seawater and molluscan aragonite/calcite.

47 and δ18O values of fossil molluscs may be used in conjunction with these calibrations to reconstruct both - seawater-δ18O and temperature.


Vanessa Schlidt1, David Evans2, Niels de Winter3, Miguel Bernecker1, Amelia Jane Davies1, Iris Arndt1, Philip Tauxe Staudigel1, Mattia Tagliavento1, Wolfgang Müller1, Jens Fiebig1
1Institute for Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany; 2School of Ocean and Earth Science, University of Southampton, Southampton, UK;Institute for Geosciences, Goethe University Frankfurt, Altenhöferallee 1, 60438 Frankfurt, Germany; 3Department of Earth Sciences, Faculty of Geosciences, Utrecht University, the Netherlands
GeoBerlin 2023