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.