From ¹⁴C/¹²C measurements towards radiocarbon dating of ice

A dry extraction method of CO₂ included in glacier ice adds a contamination equivalent to 1.8 µg modern carbon for a 35 µg C sample. This enables radiocarbon dating by accelerator mass spectrometry of 35 µg C samples to about 25 000 BP. Measured ¹⁴C/¹²C ratios are presented for a part of the Vostok ice core, and for some surface samples; high ¹⁴C/¹²C values ranging between 65 and 105 pin C indicate in-situ ¹⁴C production during the ablation. The reproducibility of radiocarbon dating of ice is demonstrated by results for some parts of the Caroline core, yielding an age versus depth profile, in which the age does not simply increases with depth. The results indicate that the accuracy of radiocarbon dating of ice is not limited by the statistical error arising in the accelerator measurements, but by the uncertainty in the contamination background of the samples and by the in-situ production of ¹⁴C.