Vertical distribution of 236U in the North Pacific Ocean

Publication date: April 2017
Source:Journal of Environmental Radioactivity, Volumes 169–170
Author(s): R. Eigl, P. Steier, K. Sakata, A. Sakaguchi
The first extensive study on ²³⁶U in the North Pacific Ocean has been conducted. The vertical distribution of ²³⁶U/²³⁸U isotopic ratios and the ²³⁶U concentrations were analysed on seven depth profiles, and large variations with depth were found. The range of ²³⁶U/²³⁸U isotopic ratios was from (0.09 ± 0.03) × 10⁻¹⁰ to (14.1 ± 2.2) × 10⁻¹⁰, which corresponds to ²³⁶U concentrations of (0.69 ± 0.24) × 10⁵ atoms/kg and (119 ± 21) × 10⁵ atoms/kg, respectively. The variations in ²³⁶U concentrations could mainly be attributed to the different water masses in the North Pacific Ocean and their formation processes. Uranium-236 inventories on the water column of each sampling station were calculated and varied between (3.89 ± 0.08) × 10¹² atoms/m² and (7.03 ± 0.50) × 10¹² atoms/m², which is lower than in former studies on comparable latitudes in the North Atlantic Ocean and the Sea of Japan. The low inventories of ²³⁶U found for the North Pacific Ocean in this study can be explained by the lack of additional input sources of artificial radionuclides, apart from global and regional/local fallout. This study expands the use of ²³⁶U as oceanographic circulation tracer to yet another ocean basin and shows that this isotope can be used for tracing circulation patterns of water masses in the Pacific Ocean.



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