First dataset of ²³⁶U and ²³³U around the Greenland coast: A 5-year snapshot (2012–2016)

We report the first combined dataset of 236U and 233U in the Greenland marine environment during the period of 2012–2016. Results are discussed in terms of time evolution and spatial distribution of 236U concentration, and atomic ratios of 236U/238U and 233U/236U. 236U concentrations along the Greenland coast are distributed within a relatively narrow range of (0.7–12.9) × 107 atom/L, corresponding to 236U/238U atomic ratios of (1.1–15.5) × 10−9.

The 233U/236U atomic ratios obtained vary from 0.12 × 10−2 to 1.16 × 10−2, with the majority distributed in the range of (0.2–0.7) × 10−2. We applied 233U/236U and 236U/238U atomic ratios in a binary mixing model to identify possible 236U source terms. The results indicate that anthropogenic 236U and 233U in Greenland surface seawater originated from the direct global fallout (DGF) and the Sellafield and La Hague reprocessing plants (RP) is diluted by a third endmember, mostly likely natural ocean water (NOW), containing marginal 236U and 233U.

A preliminary estimation of the source terms of 236U using 233U/236U atomic ratios indicate that, for both eastern and western Greenland seawater, contributions from global fallout (GF) constitute about 30% of 236U. The dominating source for 236U, i.e. 70 %, is associated to reactor 236U including discharges from RP and local reactor input in the Arctic Ocean.