²³⁶U and ¹²⁹I as tracers of water masses in the Arctic Ocean

Recently ²³⁶U attested to be a new transient oceanographic tracer: it is conservative in seawater and far from having reached steady state in the oceans. Its main sources in the North Atlantic are global fallout and European reprocessing plants. In this study, concentrations of ²³⁶U and ¹²⁹I of eight deep profiles in the Arctic Ocean collected in 2011-2012 were determined with a compact ETH Zurich AMS system (TANDY). Results on ²³⁶U/²³⁸U show a steep gradient, from the lowest ever-reported ²³⁶U/²³⁸U atomic ratio in open ocean water (5±5) x 10^-12 up to (3700±80) x 10^-12. Whereas the very low ratios are indicative for deep old waters, high ratios in shallow and surface waters show a clear signature of Atlantic Waters (AW) penetrating to the Arctic Ocean. The combination of ²³⁶U with ¹²⁹I, both being released by the nuclear reprocessing plants of Sellafield and La Hague, with a distinct temporal input function, is used to estimate transit time of AW distributions in the Arctic Ocean.