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

• Published in: Science of The Total Environment
• Main Authors: Qiao, Jixin, Heldal, Hilde Elise, Steier, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: 233U; 236U; Barents Sea; Sediment; Source term; Dating; Arctic; Arctic Ocean; Atlantic Arctic; Atlantic-Arctic
• Online Access: https://orbit.dtu.dk/en/publications/a8870edb-6d96-456d-ad62-78aac522a934; https://doi.org/10.1016/j.scitotenv.2022.157503; https://backend.orbit.dtu.dk/ws/files/283327827/1_s2.0_S0048969722046010_main_4_.pdf

This work reports the first dataset of 236 U and 233 U 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 236 U and 233 U along with 137 Cs, and 233 U/ 236 U atomic ratio were measured in six sediment profiles. The cumulative areal inventories of 236 U and 233 U obtained in this work are (3.50-12.7) × 10 11 atom/m 2 and (4.92-21.2) × 10 9 atom/m 2 , with averages values of (8.08 ± 2.93) × 10 11 atom/m 2 and (1.08 ± 0.56) × 10 10 atom/m 2 , respectively. The total quantities of 236 U and 233 U 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 236 U (6000 g) and 233 U (40-90 g) from global fallout in the Barents Sea. The integrated atomic ratios of 233 U/ 236 U ranging in (0.98-1.57) × 10 -2 reflect the predominant global fallout signal of 236 U in the Barents Sea sediments and the highest reactor- 236 U contribution accounts for 30 ± 14 % among the six sediment cores. The reactor- 236 U 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 236 U in the Barents Sea, prompt the oceanic tracer application of 236 U for studying the dynamics of the Atlantic-Arctic Ocean and associated climate changes. The 236 U- 233 U 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 236 U- 233 U pair as a useful tool for sediment dating.