Inventory and distribution of tritium in the oceans in 2016

International audience Tritium concentrations in oceans were compiled from the literature, online databases and original measurements in order to determine the global distribution of tritium concentrations according to latitude and depth in all oceans. The total inventory of tritium decay corrected...

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Published in:Science of The Total Environment
Main Authors: Oms, Pierre-Emmanuel, Bailly Du Bois, Pascal, Dumas, Franck, Lazure, Pascal, Morillon, Mehdi, Voiseux, Claire, Le Corre, Cedric, Cossonnet, Catherine, Solier, Luc, Morin, Pascal
Other Authors: Laboratoire de Radioécologie de Cherbourg-Octeville (IRSN/PSE-ENV/SRTE/LRC), Service de recherche sur les transferts et les effets des radionucléides sur les écosystèmes (IRSN/PSE-ENV/SRTE), Institut de Radioprotection et de Sûreté Nucléaire (IRSN)-Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de métrologie de la radioactivité dans l'environnement (IRSN/PSE-ENV/SAME/LMRE), Service d'analyses et de métrologie de l'environnement (IRSN/PSE-ENV/SAME), PDG-DFO, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), This work was supported by the Institut de Radioprotection et de Sûreté Nucléaire and the Institut Français de Recherche pour l'Exploitation de la Mer.
Format: Article in Journal/Newspaper
Language:English
Published: HAL CCSD 2019
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Online Access:https://hal.science/hal-02336283
https://hal.science/hal-02336283/document
https://hal.science/hal-02336283/file/0000160042_001.PDF
https://doi.org/10.1016/j.scitotenv.2018.11.448
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Summary:International audience Tritium concentrations in oceans were compiled from the literature, online databases and original measurements in order to determine the global distribution of tritium concentrations according to latitude and depth in all oceans. The total inventory of tritium decay corrected in 2016 has been estimated using evaluation of the natural and artificial contributions in 23 spatial subdivisions of the total ocean. It is determined equal to 26.8 ± 14 kg including 3.8 kg of cosmogenic tritium. That is in agreement with the total atmospheric input of tritium from nuclear bomb tests and the natural inventory at steady-state estimated from natural production rates in the literature (25.6 – 28 kg in the Earth). A global increase in tritium concentration was observed according to latitude in the Northern hemisphere with a maximum in the Arctic Ocean. The minimum tritium concentrations observed in the Southern Ocean were close to steady-state with known natural tritium deposition. We focused on the temporal evolution of surface (0 to 500 m) tritium concentrations in a selected area of the North Atlantic Ocean (30°N - 60°N) where we found the 2016 concentration to be 0.60 ± 0.05 TU (1σ). Results showed that in that area, between 1988 and 2013, tritium concentrations: i) decreased faster than the sole radioactive decay, due to a mixing with lower and lateral less concentrated waters, and ii) decreased towards an apparent steady state concentration. The half-time mixing rate of surface waters and the steady state concentration were respectively calculated to be 23 ± 5 years (1σ) and 0.38 ± 0.07 TU (1σ). This apparent steady-state concentration in the North Atlantic Ocean implies a mean tritium deposition of 1870 ± 345 Bq.m-2 (1σ), five folds higher than the known inputs (natural, nuclear tests fallout and industrial releases, ~367 Bq.m-2) in this area. Keywords: Radionuclide, Tracer, Database, Background concentration.