The issue of comparability of measurements (and thus bias, accuracy, and precision of measurement) from diverse laboratories is one which has been the focus of some attention both within the radiocarbon community and the wider user communities. As a result, the 14C community has undertaken a widescale, far-reaching, and evolving program of inter-comparisons, to the benefit of laboratories and users alike. The benefit to the users is, however, indirect, since the 14C inter-comparisons have not been used to generate "league tables" of performance, but rather to allow individual laboratories to check procedures and modify them as required.

We constructed an automated system to transform organic samples to CO2, which included several options such as: combustion in 2 steps with collection of the 2 fractions, volatile fraction combustion, and 13C sampling. The process includes organic matter combustion, CO2 drying, quantification of the mass of carbon, CO2 collection in a glass vial, and eventually 13C sampling. The system is computer-controlled and-monitored. The apparent background age of the automated system reaches 0.191 +/ 0.011 pMC (2 sigma), equivalent to a 14C age of about 51,700 yr BP, and requires only 30 min of handling, instead of the several days needed when using a manual procedure.

We have analyzed by radiocarbon 27 consecutive single rings, starting from AD 1952, of a preliminarily cross-dated section (DFR 021) of Pinus radiata, which grew in Armidale, northern New South Wales, Australia. The bomb 14C results suggested the possibility of 2 false rings, and, consequently, 2 misidentified rings in the preliminary count for this section. This possibility was supported by a better ring-width correlation between the revised DFR 021 count and other Pinus radiata chronologies in the study region. This indicated that bomb 14C is a useful tool to complement the standard techniques of dendrochronology in tree species where annual rings are not always clearly defined. Our accelerator mass spectrometry (AMS) 14C results for Armidale Pinus radiata, on a corrected timescale, can be compared with previously published atmospheric and oceanic 14C data. The data show interesting features of atmospheric circulation and the regional air-sea exchange of CO2 for the bomb period. On average, the difference between Delta-14C values for Armidale (30 degrees S) and those for Tasmania (42 degrees S) was negligible, implying a small latitudinal 14C gradient in the Southern Hemisphere. However, small offsets between Armidale and Tasmania were observed for some periods. The variation of these offsets suggests some slight changes in the relative contributions of the 2 excess 14C sources (the northern troposphere and southern stratosphere) to the southern troposphere. In the decay of bomb 14C, atmospheric 14C reached a global equilibrium at the end of the 1960s and decreased exponentially, halving every 16 years. The time for air-sea exchange of CO2 for southern Pacific mid-latitudes was found to be about 7.5 yr, which was equivalent to a CO2 flux from the atmosphere to the oceans of 21.5 moles m-2 y-1 for the 1970s.

A simple method for preparing pollen concentrates for 14C AMS dating is applied to organic and inorganic deposits from a peat bog in south Westland, New Zealand, from which preliminary AMS dating indicated age inversions and severe younger carbon contamination problems. The AMS ages of the pollen concentrates provided consistently older age estimates for each sample than ages derived from their respective organic residue or combined pollen and organic residue fractions. It is likely that the younger age estimates of the organic residue fractions result from the incorporation of younger plant material into the sample and possible contamination from younger humic acids percolating through the site.