High-resolution regional modelling of natural and anthropogenic radiocarbon in the Mediterranean Sea

A high-resolution dynamical model ( Nucleus for European Modelling of the Ocean, Mediterranean configuration -NEMO-MED12) was used to give the first simulation of the distribution of radiocarbon (C-14) across the whole Mediterranean Sea. The simulation provides a descriptive overview of both the natural pre-bomb C-14 and the entire anthropogenic radiocarbon transient generated by the atmospheric bomb tests performed in the 1950s and early 1960s. The simulation was run until 2011 to give the post-bomb distribution. The results are compared to available in situ measurements and proxy-based reconstructions. The radiocarbon simulation allows an additional and independent test of the dynamical model, NEMO-MED12, and its performance to produce the thermohaline circulation and deep-water ventilation. The model produces a generally realistic distribution of radiocarbon when compared with available in situ data. The results demonstrate the major influence of the flux of Atlantic water through the Strait of Gibraltar on the inter-basin natural radiocarbon distribution and characterize the ventilation of intermediate and deep water especially through the propagation of the anthropogenic radiocarbon signal. We explored the impact of the interannual variability on the radiocarbon distribution during the Eastern Mediterranean Transient (EMT) event. It reveals a significant increase in C-14 concentration (by more than 60 %) in the Aegean deep water and at an intermediate level (value up to 10%) in the western basin. The model shows that the EMT makes a major contribution to the accumulation of radiocarbon in the eastern Mediterranean deep waters.