Temporal and vertical distributions of anthropogenic ²³⁶U in the Japan Sea using a coral core and seawater samples

Author(s)

Aya Sakaguchi, Tomoya Nomura, Peter Steier, Robin Golser, Keiichi Sasaki, Tsuyoshi Watanabe, Tomoeki Nakakuki, Yoshio Takahashi, Hiroya Yamano

Abstract

The input history of U-236 to the surface water of the Japan Sea was reconstructed through measurement of the U-236/U-238 atom ratio in annual bands of a coral skeleton which was collected at Iki Island in the Tsushima Strait, the main entrance to the Japan Sea. The U-236/U-238 atom ratios and concentrations of U isotopes were measured for the period 1935-2010 using AMS and ICP-MS. The U-236/U-238 atom ratios revealed three prominent peaks: 4.51 x 10(-9) in 1955, 6.15 x 10(-9) in 1959 and 4.14 x 10(-9) in 1963; thereafter the isotope ratios gradually decreased over the next several decades, attaining a value of ca.1.3 x 10(-9) for the present day. A simplified depth profile model for U-236 in the Japan Sea, using the reconstructed U-236 value for the surface water together with observed depth profiles for U-236 in the water column in 2010, yielded diffusion coefficients of 3.4-5.6 cm(2)/s for 6 sampling points. The diffusion coefficient values obtained for the northern stations were relatively large, and fitting uncertainty was also larger for stations in the northern region. It may be presumed that the distribution of U-236 in the water columns have been influenced not only by diffusion but also by subduction of the surface water in the Japan Sea

Organisation(s)

Isotope Physics

External organisation(s)

University of Tsukuba, Kanazawa Gakuin University, Hokkaido University, University of Tokyo, Hiroshima University, National Institute for Environmental Studies of Japan

Journal

Journal of Geophysical Research: Oceans

Volume

121

Pages

4-13

No. of pages

10

ISSN

2169-9275

DOI

https://doi.org/10.1002/2015JC011109

Publication date

01-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

103037 Environmental physics, 105306 Oceanography

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology, Geophysics, Oceanography, Earth and Planetary Sciences (miscellaneous), Space and Planetary Science

Portal url

https://ucris.univie.ac.at/portal/en/publications/temporal-and-vertical-distributions-of-anthropogenic-236u-in-the-japan-sea-using-a-coral-core-and-seawater-samples(dfb0fd4b-2e59-485c-8ac8-325dae8966d7).html