Determining the Thermal Diffusion Factor for ⁴⁰Ar/³⁶Ar in Air To Aid Paleoreconstruction of Abrupt Climate Change

Abstract

The thermal diffusion factor (αT) of 40Ar/36Ar in air has been measured in the laboratory for the first time. The mean values of αT × 103 that we find at −30.0 °C are 9.85 ± 0.04 for air and 11.25 ± 0.03 for pure argon. The latter value is more precise than the data found in the literature. The temperature dependence of the thermal diffusion factor in air in the range −60 to −10 °C can be described by an empirical equation αT × 103 = 26.08 − 3952/〈T 〉 (±1%), where 〈T 〉 is the effective average temperature. Results of this study are valuable for reconstruction of magnitudes of abrupt climate change events recorded in Greenland ice cores. For one abrupt warming event ∼15,000 years ago, near the end of the last glacial period, these results yield a warming of 11 ± 3 °C over several decades or less. Theoretical calculations are not yet able to provide the needed accuracy, and the experimental results for the thermal diffusion factor in air should be used for paleoenvironmental studies.