On the characteristics of cosmogenic in situ 14C in some GISP2 Holocene and late glacial ice samples

In previous studies, we have shown that information on ice accumulation processes is recorded by the in situ production of 14C, from nuclear interactions of cosmic rays with oxygen in ice (Lal et al., 1997). In this report, we discuss a study of a number of Holocene and several glacial ice samples from the GISP2 core whose accumulation rates are known and which should be little affected by uncertainties in ice flow models (Cuffey et al., 1997), to determine trapping efficiencies of in situ 14C. We present new results along with discussion of the earlier results of Lal et al. (1997), which include results on partitioning of in situ 14C among the CO and CO2 phases through time in ice. The usefulness of the in situ 14C data to measurements of ice accumulation rates and ages are discussed