Inventory and distribution of tritium in the oceans in 2016

Tritiumconcentrations in oceanswere compiled fromthe literature, online databases and originalmeasurements in order to determine the global distribution of tritium concentrations according to latitude and depth in all oceans. The total inventory of tritiumdecay 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 agreementwith the total atmospheric input of tritiumfromnuclear bomb tests and the natural inventory at steady-state estimated from natural production rates in the literature (27.8-29.3 kg in the Earth). We confirmthe global increase in tritiumaccording to latitude observed in theNorthern hemisphere since 1967 with amaximumin the Arctic Ocean. The minimumtritiumconcentrations 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 degrees N-60 degrees N) where we found the 2016 concentration to be 0.60 +/- 0.10 TU (1s). Results showed that in that area, between 1988 and 2013, tritiumconcentrations: 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-timemixing rate of surfacewaters and the steady state concentration were respectively calculated to be 23 +/- 5 years (1 sigma) and 0.38 +/- 0.07 TU (1 sigma). This apparent steady-state concentration in the North Atlantic Ocean implies a mean tritium deposition of 1870 +/- 345 Bq.m(-2) (1 sigma), five folds higher than the known inputs (natural, nuclear tests fallout and industrial releases, similar to 367 Bq.m(-2)) in this area. (c) 2018 Elsevier B.V. All rights reserved.