High-resolution 14C analyses of annually-banded coral skeletons from Ishigaki Island, Japan:: implications for oceanography

We report high-resolution radiocarbon (Delta(14)C) analyses of annually-banded coral skeletons (Porites lutea) from Ishigaki Island, the Ryukyus, Japan, for the years 1985-1993. Analyses were carried out using an accelerator mass spectrometer (AMS) system at the National Institute for Environmental Studies, Tandem accelerator for Environmental Research and Radiocarbon Analysis (NIES-TERRA). Results provide a Delta(14)C time series showing significant seasonal and interannual variations superimposed on a long-term trend. Delta(14)C has a range of 66parts per thousand, from a minimum of 79parts per thousand to a maximum of 145parts per thousand. The amplitude of the seasonal variation is 15-40parts per thousand with lower Delta(14)C values in summer, which may indicate monsoon-induced local upwelling. The long-term trend of Delta(14)C is equivalent to a decrease of similar to30parts per thousand for the 8 yr from 1985 to 1993. Most of this trend probably reflects the gradual diffusion of bomb-derived C-14 from the atmosphere to the deep ocean via air-sea gas exchange and vertical movement of water masses. These results and ongoing analyses contribute to understanding of the ocean environment and ocean-atmosphere interactions in the far western subtropical Pacific. (C) 2004 Elsevier B.V. All rights reserved.