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.