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

摘要

We report high-resolution radiocarbon (Δ~(14)C) analyses of annually-banded coral skeletons (Ponies luted) 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 Δ~(14)C time series showing significant seasonal and interannual variations superimposed on a long-term trend. Δ~(14)C has a range of 66 per thousand, from a minimum of 79 per thousand to a maximum of 145 per thousand. The amplitude of the seasonal variation is 15-40 per thousand with lower Δ~(14) values in summer, which may indicate monsoon-induced local upwelling. The long-term trend of Δ~(14) is equivalent to a decrease of ～ 30 per thousand for the 8 yr from 1985 to 1993. Most of this trend probably reflects the gradual diffusion of bomb-derived ~(14)C 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.