Sources and distributions of ~(137)Cs, ~(238)Pu, ~(239,240)Pu radionuclides in the north-western Barents Sea

摘要

Sediment deposits are the ultimate sink for anthropogenic radionuclides entering the marine environment. The major sources of anthropogenic radionuclides to the Barents Sea are fallout from nuclear weapons tests, long range transport from other seas, and river and non-point freshwater supplies. In this study we investigated activity concentrations, ratios, and inventories of the anthropogenic radionuclides, ~(137)Cs, ~(238)Pu, ~(239,240)Pu in dated sediment cores collected along a north-south transect in the northwestern Barents Sea. The data were used to evaluate the influence of different sources on the derived spatial and temporal patterns of anthropogenic radionuclides in seafloor sediment deposits. Activity concentrations of ~(137)Cs ranged from <0.1 Bq/kg to 10.5 Bq/kg while ~(239,240)Pu ranged from <0.01 Bq/kg to 2.74 Bq/kg and ~(238)Pu activity concentrations ranged from <0.01 Bq/kg to 0.22 Bq/kg. Total inventories of ~(137)Cs ranged from 29.5 ± 1.5 Bq/m~2 to 152.7 ± 5.6 Bq/m~2 and for ~(239,240)Pu inventories (6 sediment layers only) ranged from 9.5 ± 0.3 Bq/m~2 to 29.7 ± 0.4 Bq/m~2. Source contributions varied among stations and between the investigated radionuclides. The ~(238)Pu/~(239,240)Pu ratios up to 0.18 indicate discharges from nuclear fuel reprocessing plants as a main contributor of plutonium. Based on ~(238)Pu/~(239,240)Pu ratio, it was calculated that up to 19-27% of plutonium is supplied from sources other than atmospheric global fallout. Taking into account Atlantic current flow trajectories and that both activity concentrations and inventories of plutonium negatively correlate with latitude, Sellafield is a major source for the Barents Sea. Concentrations and inventories of ~(137)Cs correlate positively with latitude and negatively with distance from the Svalbard archipelago. The ~(137)Cs concentrations are highest in an area of intensive melting of sea ice formed along the Siberian coast. Thus, sea ice and supplies from Svalbard may be important source of ~(137)Cs to the Barents Sea seafloor.