Comparison of CO₂ measurements by two laboratories on air from bubbles in polar ice

Abstract

The CO₂ content of air enclosed in bubbles in polar ice has been reported by our two laboratories (in Grenoble and Bern) to be representative of the atmospheric CO₂ concentration at the time the ice was formed^1,2. Such ice core studies indicate lower concentrations in ice formed at the end of the ice age, around 18,000 yr BP, and several explanations have been proposed for such a change^3,4. Both laboratories are currently measuring various ice cores in order to determine the pre-AD 1850 CO₂ level in the atmosphere, which relates to the partitioning of anthropogenic CO₂ among the atmospheric, biospheric and oceanic reservoirs. The two laboratories use different ice cores and different analytical procedures and we, therefore, need to know to what extent the measurements are quantitatively comparable. We present here the results of a comparison between the two laboratories based on measurements from the same ice core sections, which indicate that the measurements can be compared with great confidence. The results suggest that the mean CO₂ level recorded by Antartic ice for the period 800–2,500 yr BP is about 260 p.p.m.v.