Understanding source terms of anthropogenic uranium in the Arctic Ocean - First 236U and 233U dataset in Barents Sea sediments

Abstract

This work reports the first dataset of ²³⁶U and ²³³U in sediment cores taken from the Barents Sea, with the aim to better understand the source terms of anthropogenic uranium in the Arctic region. Concentrations of ²³⁶U and ²³³U along with ¹³⁷Cs, and ²³³U/²³⁶U atomic ratio were measured in six sediment profiles. The cumulative areal inventories of ²³⁶U and ²³³U obtained in this work are (3.50-12.7) × 10¹¹ atom/m² and (4.92-21.2) × 10⁹ atom/m², with averages values of (8.08 ± 2.93) × 10¹¹ atom/m² and (1.08 ± 0.56) × 10¹⁰ atom/m², respectively. The total quantities of ²³⁶U and ²³³U deposited in the Barents Sea bottom sediments were estimated to be 507 ± 184 g and 7 ± 3 g, respectively, which are negligible compared to the total direct deposition of ²³⁶U (6000 g) and ²³³U (40-90 g) from global fallout in the Barents Sea. The integrated atomic ratios of ²³³U/²³⁶U ranging in (0.98-1.57) × 10^-2 reflect the predominant global fallout signal of ²³⁶U in the Barents Sea sediments and the highest reactor-²³⁶U contribution accounts for 30 ± 14 % among the six sediment cores. The reactor-²³⁶U input in the Barents Sea sediments is most likely transported from the European reprocessing plants rather than related to any local radioactive contamination. These results provide better understanding on the source term of anthropogenic ²³⁶U in the Barents Sea, prompt the oceanic tracer application of ²³⁶U for studying the dynamics of the Atlantic-Arctic Ocean and associated climate changes. The ²³⁶U-²³³U benchmarked age-depth profiles seem to match reasonably well with the reported input function history of radioactive contamination in the Barents Sea, indicating the high potential of anthropogenic ²³⁶U-²³³U pair as a useful tool for sediment dating.

Keywords: (233)U; (236)U; Barents Sea; Dating; Sediment; Source term.