High-resolution δ13C measurements on ancient air extracted from less than 10 cm3 of ice

Leuenberger, M. C.; Eyer, M.; Nyfeler, P.; Stauffer, B.; Stocker, T. F. (2003). High-resolution δ13C measurements on ancient air extracted from less than 10 cm3 of ice. Tellus. Series B - chemical and physical meteorology, 55(2), pp. 138-144. Munksgaard 10.3402/tellusb.v55i2.16766

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A new method for δ13C analysis of very small air amounts of less than 0.5 cm3 STP was developed. This corresponds to less than 10 g of ice. It is based on the needle-crasher technique, which is routinely used for CO2 concentration measurements by infrared laser absorption. The extracted air is slowly expanded into a large volume through a water trap held at −70 °C where the pressure is measured. This sampled air is then carried by a high helium flux through a preconcentration system to separate CO2 cryogenically from the air. The small CO2 amount is then released into a low helium stream which forces the CO2 via an open split device to a mass spectrometer. The overall precision, based on replicates of standard air without crushing, is significantly better than 0.1‰ for a single analysis, and is further improved by a triplicate measurement of the same sample through a specially designed gas splitter. Performing δ13C measurements on ice air through the whole system, we reach a reproducibility of 0.12‰. Additional information is obtained through amplitude vs. pressure ratio determination, which results in a good control of the CO2 concentration (1 ppm precision for 1σ). The new method allows us to produce highly resolved records of atmospheric δ13C from air enclosed in ice, which is required to better understand the evolution and the temporal variability of the global carbon cycle.

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