Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives |
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| Institution: | 1. State Key Laboratory of Radiation Medicine and Protection, School for Radiological and Interdisciplinary Sciences (RAD-X), Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions and School of Radiation Medicine and Protection, Soochow University, Suzhou 215123, China;2. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China;3. Tianjin Center, China Geological Survey, CGS, Key Laboratory of Coast and Quaternary Geo-Environment, Tianjin 300170, China;4. College of Environmental Science and Engineering, Yangzhou University, Yangzhou 225127, China;5. Department of Oncology, University of Oxford, Old Road Campus Research Building, Old Road Campus, Roosevelt Drive, Oxford, OX37DQ, United Kingdom;6. The Key Laboratory of Coastal and Island Development of Ministry of Education, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China;1. The Key Laboratory of Coastal and Island Development of Ministry of Education, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China;2. State Key Laboratory of Pollution Control & Resources Reuse, School of the Environment, Nanjing University, Nanjing 210046, China;3. College of Environmental Science and Engineering, Yangzhou University, Yangzhou 225009, China;1. Institut de Ciència i Tecnologia Ambientals & Departament de Física, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain;2. Laboratory of Ion Beam Physics, ETH-Zurich, Otto Stern Weg 5, 8093 Zurich, Switzerland;3. Institute of Biogeochemistry and Pollutant Dynamics, Environmental Physics, ETH-Zurich, Universitätstrasse 16, 8092 Zurich, Switzerland;4. School of Science, Centre for Marine Ecosystems Research, Edith Cowan University, Joondalup, WA 6027, Australia;5. Oceans Institute and School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia |
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| Abstract: | Historical 239Pu activity concentrations and 240Pu/239Pu atom ratios were determined in skeletons of dated modern corals collected from three locations (Chuuk Lagoon, Ishigaki Island and Iki Island) to identify spatial and temporal variations in Pu inputs to the Northwest Pacific Ocean. The main Pu source in the Northwest Pacific is fallout from atmospheric nuclear weapons testing which consists of global fallout and close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands. PPG close-in fallout dominated the Pu input in the 1950s, as was observed with higher 240Pu/239Pu atom ratios (> 0.30) at the Ishigaki site. Specific fallout Pu contamination from the Nagasaki atomic bomb and the Ivy Mike thermonuclear detonation at the PPG were identified at Ishigaki Island from the 240Pu/239Pu atom ratios of 0.07 and 0.46, respectively. During the 1960s and 1970s, global fallout was the major Pu source to the Northwest Pacific with over 60% contribution to the total Pu. After the cessation of the atmospheric nuclear tests, the PPG again dominated the Pu input due to the continuous transport of remobilised Pu from the Marshall Islands along the North Equatorial Current and the subsequent Kuroshio Current. The Pu contributions from the PPG in recent coral bands (1984 onwards) varied over time with average estimated PPG contributions between 54% and 72% depending on location. |
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