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

摘要

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 I-129 in corals from the southern hemisphere show the increasing trend of I-129 concentrations in the marine environment caused by HNA. Here we show time series of I-129/(127(stable))1 isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record I-129 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 (I-129/I-127 similar to 31.5 x 10(-12)) in both the Baler and Parola records, each attributed to the year 1962 - the year with the highest recorded amount of I-129 release from nuclear bomb testing. This 1962 I-129 bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better thhn the well-known coral C-14 bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident I-129 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 I-129 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 I-129/(127) I isotopic ratios (i.e., 22.8 to 38.9 x 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 I-129 releases of different HNA. These results possibly indicate the presence of unknown sources of I-129 in the South China Sea region. (C) 2016 Elsevier Ltd. All rights reserved.