Radionuclides in the bottom sediments at the Komsomolets nuclear submarine wreck site (Norwegian Sea): fluxes and radioecology.

The vertical distribution of anthropogenic (239+240Pu, 238Pu) and natural (210Pbex, 226Ra, 232Th, 40K) radionuclides was studied in bottom sediments at the Komsomolets submarine wreck site (eastern deep Norwegian Sea) and a reference station (western deep Norwegian Sea). Maximum 239+240Pu activity concentrations were observed in surface sediments (0-1 cm): 845 ± 48 mBq·kg-1 at the wreck site and 583 ± 41 mBq·kg-1 (layer 0-0.5 cm) at the reference station, decreasing nearly exponentially with depth. A similar pattern was found for 238Pu (3-35 mBq·kg-1). Natural radionuclides showed relatively uniform distributions with slight increases at depth. Lower radionuclide activities at the reference station may reflect differences in sediment composition and accumulation conditions. Geochronological dating using 210Pbex and, for the first time, plutonium isotopes yielded sedimentation rates of 0.09 ± 0.02 and 0.08 ± 0.02 cm yr-1, and mass accumulation rates of 0.041 ± 0.006 and 0.043 ± 0.006 g cm-2·yr-1 at the wreck site and a reference station, respectively. These parameters enabled reconstruction of radionuclide sedimentation fluxes over the past 60 years. The reconstructed sediment records indicated an approximately threefold increase in 239+240Pu and 238Pu fluxes from the mid-1950s. Continued plutonium inputs through oceanic transport pathways, including bottom-current and sea-ice-mediated transport, may contribute to this trend. Screening radioecological assessment demonstrated that current radionuclide levels in bottom sediments at the Komsomolets site do not exceed screening criteria. No evidence of a detectable local plutonium contribution from the Komsomolets wreck was found in the investigated sediments.