Reconstruction of the temporal distribution of 236U/238U in the Northwest Pacific Ocean using a coral core sample from the Kuroshio Current area

The temporal distribution of 236U in the Northwest Pacific Ocean was reconstructed through measurements of the annual changes in 236U/238U atom ratios in a coral core collected from Kume Island located within the Kuroshio Current region. In total, 74years (1940–2014) of temporal trend of 236U/238U a...

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Bibliographic Details
Published in:Marine chemistry 2017-03, Vol.190, p.28-34
Main Authors: Nomura, Tomoya, Sakaguchi, Aya, Steier, Peter, Eigl, Rosmarie, Yamakawa, Akane, Watanabe, Takaaki, Sasaki, Keiichi, Watanabe, Tsuyoshi, Golser, Robin, Takahashi, Yoshio, Yamano, Hiroya
Format: Article
Language:English
Subjects:
236U
236U/238U atom ratios
AMS
Coral core
Northwest Pacific Ocean
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Summary:The temporal distribution of 236U in the Northwest Pacific Ocean was reconstructed through measurements of the annual changes in 236U/238U atom ratios in a coral core collected from Kume Island located within the Kuroshio Current region. In total, 74years (1940–2014) of temporal trend of 236U/238U atom ratios were reconstructed using Accelerator Mass Spectrometry (AMS). The annually resolved 236U/238U ratios showed a strong increase from 1952, and two prominent peaks were found in the annual bands for 1954 (11.0±1.2×10−9) and 1958 (8.55±1.17×10−9); also an enhanced peak was observed for the band of 1963 (3.51±0.20×10−9). These peaks coincided with the occurrence of large nuclear tests in the Pacific Proving Grounds and/or the highest global fallout rate, suggesting a clear influence of these nuclear events on 236U/238U atom ratios. Furthermore, the coral results showed some disagreement with the annual changes for 236U in East Asian corals collected at the entrance to the Sea of Japan. Based on these results, the mixing ratios of the surface seawater currents in the Northwest Pacific Ocean have been estimated. •The temporal distribution of 236U in the Northwest Pacific Ocean was reconstructed.•Prominent 236U input peaks were 1954 and 1958 rather than 137Cs maximum age, 1963.•Large nuclear tests in the PPG clearly influenced on the 236U input to the Pacific.•236U and 236U/238U can be used as robust oceanic circulation and mixing tracers.
ISSN:0304-4203
1872-7581
DOI:10.1016/j.marchem.2016.12.008