| Summary: | The Sellafield nuclear fuel reprocessing plant is estimated to be the largest single source of global anthropogenic radiocarbon discharge. This study addresses the impact of these releases on the Irish coastal marine environment. Spatial trends in the (super 14) C content of seaweed (Fucus spp.) were assessed by collecting and analyzing samples from well-distributed locations around the Irish coastline. Temporal trends were studied by comparing (super 14) C concentrations in present-day samples with levels found in archive material collected at the same locations during research campaigns conducted in the mid-1980s and mid-1990s. The impact of (super 14) C discharged from Sellafield was found to be most apparent in seaweeds from the northeastern Irish coast. This indicates that the pattern of residual currents and, in particular, the south to north transfer of water known to predominate in the Irish Sea, largely controls the spatial distribution of (super 14) C releases. Maximum (super 14) C discharge levels to the marine environment from Sellafield (between 12 and 13 TBq yr (super -1) ) were mirrored by peak concentrations found in seaweed from the mid-1990s and in present-day samples (highest recorded value of 130.4 pMC). Concentrations of (super 14) C in seaweed from the west coast of Ireland correspond closely with values measured for seaweeds from the Atlantic coast of northwest Spain and do not appear to be significantly affected by Sellafield discharges.
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