Two 60-year records of ~(129)I from coral skeletons in the South Pacific Ocean

摘要

~(129)I is an important radionuclide tracer for certain natural and anthropogenic nuclear processes. ~(129)I has a half-life of 15.7 Myr and can be measured by accelerator mass spectrometry (AMS). This paper presents ~(129)I results made at the University of Arizona with a NEC 3 MV Pelletron accelerator. For this study, we selected living corals from the Solomon Islands and Easter Island to monitor increases in anthropogenic I in the surface waters of the Pacific Ocean. ~(129)I/~(127)I values were measured in cores taken from massive Porites head coral skeletons. Typical sample sizes for this study were 10 g for the Solomon Islands corals, and 30 g for the Easter Island corals. Temporal resolution was semi-annual at the Solomon Islands, and annual at Easter Island. Iodine was extracted from the corals without the use of carrier iodine. Results of our study produced records at both sites from roughly 1935 to 1996. While ~(129)I/~(127)I values have increased at both locations since the beginning of atmospheric nuclear weapons testing, different bomb-pulse curves at these sites suggest different transport mechanisms and/or ~(129)I inputs at the two sites. The implications of these measurements are discussed below.