Sources of ¹³⁷Cs to an Arctic fjord (Hornsund, Svalbard)

Although primary sources of anthropogenic ¹³⁷Cs have decreased nowadays, the Arctic is exposed to a variety of secondary sources. These include riverine run-off, oceanic currents, drifting sea ice, melting glaciers and permafrost. Recent reports underline the role of glaciers, specifically cryoconite holes, in radionuclide accumulation. Therefore, this study investigates the hypothesis that melting glaciers are an important means of delivering ¹³⁷Cs for Arctic fjord (Hornsund, Svalbard). As marine sediments are the final sink for most contaminants, seven 30-40 cm long sediment cores collected in 2016 were investigated for ¹³⁷Cs activity concentration. Five were collected in a transect from the central to the outer part of the fjord while two were collected within one km of the different melting tidewater glaciers. Sediment layers were dated using ²¹⁰Pb to reveal the history of ¹³⁷Cs accumulation. The measured ¹³⁷Cs activity concentrations ranged from <0.1 to 7.7 Bq kg^-1. The activity concentrations ranging from 0.3 to 3.1 Bq kg^-1 were measured in surface (0-2 cm) sediments. The total ¹³⁷Cs inventories were calculated for five station and ranged from 322 to 908 Bq m^-2, of which 29-34 Bq m^-2 were deposited within the last decade. At two stations characterized by largest sediment accumulation rates only the last decade inventories were calculated and they ranged from 13 to 444 Bq·m^-2. The mean of ¹³⁷Cs fluxes calculated for last decade ranged from 2.7 to 44.1 Bq m^-2yr^-1. The history of ¹³⁷Cs environmental inputs was well revealed in the sediments as the ¹³⁷Cs penetration depth agreed with the time of its introduction to the Arctic and the most pronounced ¹³⁷Cs activity concentration peak was found in sediments dated for circa 1963. Although ¹³⁷Cs fluxes and inventories were largest in the glacial bay (Brepollen), the ¹³⁷Cs was diluted in a large amount of sedimenting material. Based on the results in this study, the glaciers do not appear to act as important sources of ¹³⁷Cs to the marine environment in the Hornsund fjord.