Approx age of ice based on layer counting and delta 18O data for trapped air (Grootes et al., 1993; Sowers et al., 1993; Meese et al., 1994a; Stuiver et al., 1995). Typical errors in determination of 14C concentration in recent samples are 50-60 atoms/g, which includes statistical errors and uncertainties. The larger errors arise from multiple extractions, and in samples from depths 100.4 to 1518 from 14C-decay corrections.