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
aragonites precipitated in a wide range of temperatures (1‒850°C). We
observe no offset in clumped isotope values between aragonitic
foraminifera, mollusks, and abiogenic aragonites or between aragonites
and calcites, eliminating the need for 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.