Historical record of nuclear activities from 129I in corals from the northern hemisphere (Philippines)

Publication date: November 2016
Source:Journal of Environmental Radioactivity, Volume 164
Author(s): Angel T. Bautista, Hiroyuki Matsuzaki, Fernando P. Siringan
Iodine-129 is a long-lived fission product that is majorly released in human nuclear activities (HNA) such as nuclear bomb testing, nuclear fuel reprocessing, and nuclear accidents. It is a good environmental tracer and former measurements of ¹²⁹I in corals from the southern hemisphere show the increasing trend of ¹²⁹I concentrations in the marine environment caused by HNA. Here we show time series of ¹²⁹I/^127(stable)I isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record ¹²⁹I released from HNA in even greater, unprecedented detail. Corals were taken from the Pacific Ocean (Baler) and South China Sea (Parola) sides of the Philippines. We observed nearly identical peaks (¹²⁹I/¹²⁷I ∼ 31.5 × 10⁻¹²) in both the Baler and Parola records, each attributed to the year 1962 – the year with the highest recorded amount of ¹²⁹I release from nuclear bomb testing. This 1962 ¹²⁹I bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better than the well-known coral ¹⁴C bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident ¹²⁹I signals in years 1977, 1980, and 1986, concurrently in Parola and with 9 to 11-year lags in Baler. This discrepancy in timing suggests that ¹²⁹I was transported to the South China Sea and Pacific Ocean sides of the Philippines directly from the atmosphere and through prevailing ocean currents, respectively. Lastly, we observed surprisingly high ¹²⁹I/¹²⁷I isotopic ratios (i.e., 22.8 to 38.9 × 10⁻¹²) in the Parola record after the year 1996, which is in contrast to the decreasing trend observed in the Baler record and in published ¹²⁹I releases of different HNA. These results possibly indicate the presence of unknown sources of ¹²⁹I in the South China Sea region.

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