Temperature Dependence of Clumped Isotopes (∆ 47 ) in Aragonite

Abstract

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°C), which we combine with clumped isotope data from natural and synthetic aragonites from a wide range of temperatures (1–850°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°C) datapoints in linear clumped isotope calibrations causes them to underestimate temperatures of cold (1–18°C) carbonates by 2.7 ± 2.0°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.