Temperature Dependence of Clumped Isotopes ( increment 47) in Aragonite

Clumped isotope thermometry can independently constrain the formation temperatures of carbonates, but a lack of precisely temperature-controlled calibration samples limits its application on aragonites. To address this issue, we present clumped isotope compositions of aragonitic bivalve shells grown under highly controlled temperatures (1-18 degrees C), which we combine with clumped isotope data from natural and synthetic aragonites from a wide range of temperatures (1-850 degrees C). We observe no discernible offset in clumped isotope values between aragonitic foraminifera, mollusks, and abiogenic aragonites or between aragonites and calcites, eliminating the need for a mineral-specific calibration or acid fractionation factor. However, due to non-linear behavior of the clumped isotope thermometer, including high-temperature (>100 degrees C) datapoints in linear clumped isotope calibrations causes them to underestimate temperatures of cold (1-18 degrees C) carbonates by 2.7 +/- 2.0 degrees C (95% confidence level). Therefore, clumped isotope-based paleoclimate reconstructions should be calibrated using samples with well constrained formation temperatures close to those of the samples.

Automated summary

Clumped isotope thermometry can independently constrain the formation temperatures of carbonates, but calibration samples close to the formation temperatures of the samples are needed to accurately perform paleoclimate reconstructions.