Discussion on differences in radiocarbon ages reported from St. Kitts, West Indies

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M. J. Roobol writes: In a recent paper, P. E. Baker (1985), describes differences in radiocarbon ages obtained from pyroclastic deposits of Mt Misery, St Kitts. The ages reported by Roobol et al. 1981 are consistently older than those reported by Baker (1985). Unit E pyroclastic flow deposits of Mt Misery yielded a range of ages from 2280 to 3060 years in the earlier work and 2030 to 2060 in the later work. In one instance the same carbonized tree trunk yielded an age of 2860 ± 105 (Roobol et al. 1981) compared with 2050 ± 40 and 2120 ± 40 (Baker 1985). The reason for this systematic difference does not lie in the use of different radiocarbon dating laboratories, but in the nature of the material submitted to them. The older ages obtained by us result from a field decontamination procedure which we developed and have used in the Lesser Antilles since 1971. We regard all exposed carbonized wood on the green tropical volcanoes of the Lesser Antilles as contaminated by the decomposed remains of modern plant roots and we apply our decontamination procedure at all collection sites. Our age dates are consistently older because we submit less contaminated material and we regard them as more closely approaching the age of the deposit. Some discussion of the justification and nature of the simple decontamination procedure is given here as its application may be of wider interest. In 1971 Alan Smith and I began collecting carbonized wood on Mt Pelée,