Clumped isotope analyses on biogenic aragonites and their use in paleoclimate reconstructions

Understanding the response of Earth’s climate to perturbations requires accurate and detailed reconstructions of past climate states (e.g. Tierney et al., 2020). The clumped isotope thermometer has the potential to constrain the formation temperatures of carbonates independent from the (isotopic) composition of the precipitation fluid and regardless of the origin (e.g. taxonomy) of the carbonate producer (e.g. Anderson et al., 2020), making it an ideal tool for paleoclimate reconstructions. Unfortunately, it is still not fully certain whether the clumped isotope composition of different carbonate minerals (e.g. calcite, aragonite, dolomite) responds similarly to changes in formation temperatures or variations in the temperature at which the acid reaction takes place during analyses (e.g. Guo et al., 2009; Müller et al., 2017). This uncertainty complicates the application of clumped isotope thermometry to biogenic aragonite shells of bivalves and gastropods, as well as to chemically precipitated travertines and speleothems.

To solve part of these issues, we present a new dataset consisting of clumped isotope measurements on aragonitic Arctica islandica bivalves grown at precisely controlled temperatures (1.1±0.2°C - 18±0.3°C). We compare our data with preexisting clumped isotope calibration datasets spanning a wide temperature range and containing both aragonite and calcite samples. Our clumped isotope data with well-defined formation temperatures allows us to constrain small but important differences between previously published calibration datasets and sheds light on the temperature dependence of clumped isotope composition of aragonites. We use these new insights into the clumped isotope thermometer at low temperatures to produce seasonally resolved paleotemperature reconstructions from excellently preserved aragonitic bivalves from the Pliocene Warm Period, a valuable analogue for future climate under intermediate greenhouse gas emission scenarios (SSP2-4.5; Meinshausen et al., 2020).

References

Anderson et al. GRL 48, e2020GL092069, https://doi.org/10.1029/2020GL092069, 2021.

Guo et al. GCA, 73, 7203–7225, https://doi.org/10.1016/j.gca.2009.05.071, 2009.

Meinshausen et al. GMD 13, 3571–3605, https://doi.org/10.5194/gmd-13-3571-2020, 2020.

Müller et al. Chem. Geol., 449, 1–14, https://doi.org/10.1016/j.chemgeo.2016.11.030, 2017.

Tierney et al. Science 370, https://doi.org/10.1126/science.aay3701, 2020.