PRELIMINARY TEST OF THE EA-AGE3 SYSTEM FOR 14C MEASUREMENT OF CaCO3 SAMPLES AND CORAL-BASED ESTIMATION OF MARINE RESERVOIR CORRECTION IN THE OGASAWARA ISLANDS, NORTHWESTERN SUBTROPICAL PACIFIC

We conducted a preliminary test of the coupled system of an elemental analyzer and the automated graphitization equipment Ionplus AGE3 (EA-AGE3 method) for accelerator mass spectrometry radiocarbon (AMS C-14) measurements of CaCO3 samples, by comparing with the conventional method where the samples are hydrolyzed in phosphoric acid and resulting CO2 gas is manually graphitized in a vacuum line (HPA method). The samples used in the test were the IAEA C2 travertine, fossil and modern corals from the Ryukyu Islands and the Ogasawara Islands, respectively (both are located in the northwestern subtropical Pacific). Results indicate that, relative to the HPA method, the EA-AGE3 method tends to cause an increase of similar to 0.4-0.5 pMC with more widely scattered data. This is presumably due to C-14 contamination in the EA (the most likely cause seems to be a memory effect of C-14); this effect could be reduced by careful optimization of conditions and procedures in the EA process. The C-14 data of pre-bomb annual bands (1931-1949 AD) in the modern Ogasawara coral obtained by the HPA method were used to estimate the marine reservoir C-14-age correction (Delta R) of this region; it ranges from -109 yr to -28 yr with the mean value with standard deviation of -81 +/- 29 yr.