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Sources of plutonium to the tropical Northwest Pacific Ocean (1943-1999) identified using a natural coral archive

Lindahl, P.,Asami, R.,Iryu, Y.,Worsfold, P.,Keith-Roach, M.,Choi, M.S. Pergamon Press ; Elsevier Science Ltd 2011 Geochimica et cosmochimica acta Vol.75 No.5
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The Pu isotopes, 239Pu and 240Pu, were determined in annually-banded skeletons of an accurately dated (1943-1999) modern coral (Porites lobata) from Guam Island to identify historical Pu sources to the tropical Northwest Pacific Ocean. Activity concentrations of 239+240Pu and 240Pu/239Pu atom ratios were determined in the dated coral bands using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands and global fallout were identified as the two main sources. The Guam site was dominated by PPG close-in fallout in the 1950s, with an average 240Pu/239Pu atom ratio of 0.315+/-0.005. In addition, a higher 240Pu/239Pu atom ratio (0.456+/-0.020) was observed that could be attributed to fallout from the ''Ivy Mike'' thermonuclear detonation in 1952. The atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low 240Pu/239Pu atom ratio (∼0.18). Recent coral bands (1981-1999) are dominated by the transport of remobilised Pu, with high 240Pu/239Pu atom ratios, from the Marshall Islands to Guam Island along the North Equatorial Current (NEC). This remobilised Pu was estimated to comprise 69% of the total Pu in the recent coral bands, although its contribution was variable over time.
2
Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives

Lindahl, Patric,Andersen, Morten B.,Keith-Roach, Miranda,Worsfold, Paul,Hyeong, Kiseong,Choi, Min-Seok,Lee, Sang-Hoon Elsevier 2012 Environment international Vol.40 No.-
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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. Highlights ► Low levels of Pu isotopes determined in dated NW Pacific coral samples. ► Contribution from different Pu sources estimated. ► Unusual high 240Pu/239Pu ratio of 0.46 is attributed to 1952 Ivy Mike detonation. ► Identified Pu contribution from the Nagasaki atomic bomb.

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