Spatial and temporal variations of 14C in Fucus spp. in Swedish coastal waters

Abstract

Carbon-14 (14C) dominates the collective effective dose from globally dispersed long-lived radionuclides produced by and released from the nuclear power industry. Literature data on the discharge of 14C to the marine environment from nuclear power plants (NPPs) and its dispersion in the marine ecosystem are sparse. The local marine 14C background must be determined before the 14C enrichment in the marine environment from a NPP can be estimated. This is not trivial since marine activity concentrations of 14C vary spatially, partly due to long-range transport of 14C from other anthropogenic sources. We have analysed 14C in samples of several species of brown algae (Fucus spp.) collected at 45 sites along the Swedish coast in 2020. At sites remote from NPPs, the 14C activity concentrations per unit mass of carbon (here expressed as Fraction Modern, F14C) were significantly higher on the west coast than on the east coast (F14C up to about 1.10 in Skagerrak, and about 1.01, close to atmospheric levels, in the Baltic Sea and the Gulf of Bothnia). On the west coast, F14C showed a strong correlation with salinity, both of which increased towards the north. This indicates that 14C is carried from other anthropogenic sources (e.g. from the nuclear fuel reprocessing plants at La Hague and Sellafield). The highest value of F14C observed was close to the Ringhals NPP on the west coast, F14C ≈ 1.3, which is higher than expected in the terrestrial environment of this NPP. We also report on temporal variations of F14C in Fucus spp. collected at Särdal on the Swedish west coast during the period 1967–2020. The values of F14C in the Särdal marine samples collected after the 1990s are clearly higher than F14C in clean air CO2, indicating contributions of 14C of anthropogenic origin.