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 deg C), which we combine with clumped isotope data
from aragonites precipitated in a wide range of temperatures (1‒850 deg
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 deg C) datapoints in linear clumped isotope
calibrations causes them to underestimate temperatures of cold (1‒18 deg
C) carbonates by 2.7 +/- 2.0 deg 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.