Radiocarbon age assessment of a new, near background IAEA C-14 quality assurance material

The C-14 Quality Assurance Programme coordinated by the IAEA (Rozanski et al. 1992) prepared a set of five new intercomparison materials, including 40-50 ka old subfossil wood excavated from New Zealand peat bogs (IAEA C-4 standard). Statistical analysis of 79 C-14 measurements made on the wood indicated considerable variation in the results, with a marked skewness toward more modern values. The wide range of results and the possibility of inhomogeneity within the standard prompted the recovery and analysis of replacement material. The new subfossil wood sample is kauri (Agathis australis), at least 50 ka old, excavated from a swamp in Northland. It is in the form of a single plank, 6 m long, weighing 80 kg. It will be forwarded to the IAEA in Vienna for milling and distribution. Subsamples were obtained from both ends of the plank and analyzed by six laboratories. We present here the results of these analyses and compare them with the previous IAEA intercalibration results for the C-4 standard.