EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Sea shells record large biases from the marine bomb-14C curve in NW European seawater between the late 1960s and 2019

Maxi Castrillejo1, Christopher A. Richardson2, Rob Witbaard3, Rob Dekker3, Caroline Welte1,4, Lukas Wacker1, Christiane Yeman1, Núria Casacuberta1, Hans-Arno Synal1, and Marcus Christl1
Maxi Castrillejo et al.
  • 1Laboratory of Ion Beam Physics, ETH-Zürich, Zurich, Switzerland (
  • 2School of Ocean Sciences, Bangor University, Bangor, United Kingdom
  • 3NIOZ and Utrecht University, Texel and Utrecht, The Netherlands
  • 4Biogeosciences, ETH-Zurich, Zurich, Switzerland

The Northeast Atlantic alone has received 1.2 PBq of 14C as liquid and gaseous releases from European nuclear fuel reprocessing plants (NRPs) between the 1950s and present. The input of reprocessing-14C has the potential to elevate the regional 14C content of seawater, sediments and marine biota above the ambient levels expected from the bomb-14C. Yet, a comprehensive assessment of the time evolution of F14C in seawater is still missing for the Northwestern European Seas. Moreover, the least-well studied period of time (1990’s onward) corresponds to the largest liquid 14C releases reported by the Sellafield and La Hague NRPs. In this study, we aim at better constraining the temporal changes of F14C between the late 1960s and 2019, and to delimit the area of influence of reprocessing discharges with regard to 14C. To this end, we combine Accelerator Mass Spectrometry techniques and a novel archive of bivalve shells that inhabited the Irish Sea, the North Sea, Norway and the Bay of Biscay throughout the main period of reprocessing-14C discharge. The shells are made of aragonite, and thus, they can be used as an analogue of the past seawater F14C. The shell-based F14C data can be accurately placed in the temporal context because the animals have a known capture date and short lifespan of two years. The reconstructed F14C values vary between ~1 and ~3 after the 1970s. This range of F14C values is even larger than the one displayed by the atmospheric bomb peak (1 - 1.9). To investigate if the excess 14C is related to the reprocessing releases, we use a simple box model that simulates the seawater F14C by mixing bomb and reprocessing-14C, as well as the naturally occurring 12,14C. In shells from the southern North Sea, the F14C increases 0.1-0.4 above ambient levels after the mid-1990s in response to increased discharge rates of liquid 14C from the La Hague plant. Similarly, the shells collected in the Irish Sea show two consecutive peaks in the mid-1990s (F14C ~ 2.0) and 2000s (F14C ~ 2.2) that can be attributed to peak discharge rates of liquid 14C reported by Sellafield. The F14C in shells from the eastern coast of the UK and Norway are within the range of the ambient values, which indicates the expected rapid dilution of the reprocessing signal with open ocean waters. In previous studies, the bomb-14C marine curve has been used as a benchmark, among others, to estimate the age and growth rate of calcifying animals, to date marine sediments, and to investigate water mass mixing and circulation timescales. Given the biases from the marine bomb-14C curve unraveled by the shell data, we suggest that liquid releases from the NRPs should not be disregarded when applying 14C as a chronological or circulation tool to marine samples collected in the Irish Sea and parts of the North Sea over the last 5 decades.

How to cite: Castrillejo, M., Richardson, C. A., Witbaard, R., Dekker, R., Welte, C., Wacker, L., Yeman, C., Casacuberta, N., Synal, H.-A., and Christl, M.: Sea shells record large biases from the marine bomb-14C curve in NW European seawater between the late 1960s and 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1495,, 2019

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