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The dual-clumped isotope thermometer as a tool to identify and correct for isotopic disequilibrium in the clumped isotope composition of biogenic carbonate

The clumped isotope composition (∆47) of marine biogenic carbonates is an increasingly applied proxy for temperature reconstruction. The clumped isotope measurement is particularly valuable as ∆47 is independent of the δ18O of seawater. However, kinetic effects during biomineralization can impact the ∆47 of some marine archives, impeding accurate paleotemperature reconstruction.

Dual carbonate clumped isotope thermometry (i.e., simultaneous ∆47 and ∆­48 measurements on a single carbonate) has the potential to identify kinetically driven isotopic disequilibrium in biogenic carbonate and facilitate the reconstruction of carbonate formation temperature independent of kinetic biases. We present the dual-clumped isotope compositions of several key marine archives, historically used to reconstruct changes in sea surface temperature and δ18O across the Phanerozoic. These include brachiopods, cold and warm-water corals, and belemnites.

Corals and brachiopods exhibit disequilibrium ∆47 and ∆48, corresponding kinetic effects relating to mixing of an equilibrium DIC pool with kinetically derived HCO3- produced by hydration and hydroxylation of CO2. We demonstrate how measurement of the dual clumped isotope composition of corals and brachiopods can be used to correct for kinetic bias in ∆47, yielding more accurate temperature reconstructions (<±3°C at the 95% confidence interval). Dual clumped isotope thermometry, therefore, (re-)opens brachiopod and coral archives for reconstruction of shallow and intermediate water mass temperatures on geological timescales. Furthermore, we confirm that belemnites precipitate calcite in dual-clumped isotope equilibrium yielding precise growth temperatures, thus belemnite ∆47 may be reliably used as a proxy for Mesozoic sea surface temperatures (<±2.5°C at the 95% confidence interval).


Amelia Davies1, Uwe Brand2, Jacek Raddatz1, Eberhard Gischler1, Gregory Price3, Weifu Guo4, Miguel Bernecker1, Mattia Tagliavento1, Jens Fiebig1
1Institut für Geowissenschaften, Goethe Universität, Frankfurt am Main, Germany; 2Department of Earth Sciences, Brock university, St. Catherines, Ontario, Canada.; 3Department of Geological Sciences, The University of Plymouth, Plymouth, UK; 4Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, United States
GeoMinKöln 2022