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Disequilibrium Uranium (234U/238U) in Natural Aqueous Objects and Climatic Variations: World Ocean


Natural waters usually demonstrate the disturbance of radioactive equilibrium between parent 238U and and daughter 234U (usually, 234U/238U ≈ 0.8–3 in activities). The ratio of 234U/238U > 10 found in groundwaters can be explained by climatic variations, and it is result of 234U accumulation in permafrost rocks during cold periods and its more rapid loss compared to 238U during thawing. We tested this hypothesis for data on uranium isotope composition in water, and also chemo- and biogenic formations of the World Ocean. Most significant enrichment in 234U is discovered in the northern and internal seas during climatic warmings, which is consistent with an inferred influence of the permafrost formation and degradation on the anomalous increase of 234U/238U in groundwaters. Sampling of the Barents Sea shows that the uranium-234 enrichment in oceanic water increases with increase (a) of isolation from oceanic circulation system, (b) of the relative length of the coastal line, (c) and the contribution of continental waters to the chemical balance of the basin.

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We are grateful to O.L. Balakina, the head of the Hydrometeorological Department of the Northern UGMS and chief of the R/V Mikhail Somov expedition, for providing favorable conditions for the performance of research works and uninterrupted attention to our studies. We also thank the captain and crew of the R/V Mikhail Somov for the assistance in solving the problems arising during the expedition.


Expedition works were carried out in the framework of the Transarctica-2019 project.

Analytical works were financially supported by the Russian President Foundation for Support of Young Scientists, project no. МК-1919.2020.5. Data interpretation was supported by the Russian Science Foundation, project no. 20-77-10057.

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Correspondence to I. V. Tokarev or E. Yu. Yakovlev.

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Translated by M. Bogina

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Tokarev, I.V., Yakovlev, E.Y., Zykov, S.B. et al. Disequilibrium Uranium (234U/238U) in Natural Aqueous Objects and Climatic Variations: World Ocean. Geochem. Int. 59, 895–902 (2021).

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  • disequilibrium uranium
  • 234U/238U
  • climatic variations
  • permafrost
  • World Ocean