Instruments and Methods A high-precision method for measurement of paleoatmospheric CO2 in small polar ice samples

We describe a high-precision method, now in use in our laboratory, for measuring the CO2 mixing ratio of ancient air trapped in polar ice cores. Occluded air in ice samples weighing 8–15 g is liberated by crushing with steel pins at –358C and trapped at –2638C in a cryogenic cold trap. CO2 in the extracted air is analyzed using gas chromatography. Replicate measurements for several samples of highquality ice from the Siple Dome and Taylor Dome Antarctic ice cores have pooled standard deviations of <0.9 ppm. This high-precision technique is directly applicable to high-temporal-resolution studies for detection of small CO2 variations, for example CO2 variations of a few parts per million on millennial to decadal scales.