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

Abstract

<p><strong>Abstract.</strong> A high-resolution dynamical model (NEMO-MED12) was use to give the first simulation of the distribution of radiocarbon (<sup>14</sup><i>C</i>) across the whole Mediterranean Sea. The simulation provides a descriptive overview of both the natural pre-bomb <sup>14</sup><i>C</i> and the entire anthropogenic radiocarbon transient generated by the atmospheric bomb tests performed in the 1950s and early 1960s. The simulation was run until 2010 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 ventilation 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 event (EMT). It reveals a significant increase in <sup>14</sup><i>C</i> concentration (by more than 60 ‰) in the Aegean deep water, and at 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.</p>

IDENTIFICATION IN PORE WATERS OF RECYCLED SEDIMENT ORGANIC MATTER USING THE DUAL ISOTOPIC COMPOSITION OF CARBON (δ13C AND Δ14C): NEW DATA FROM THE CONTINENTAL SHELF INFLUENCED BY THE RHÔNE RIVER

“…Identification in Pore Waters 1623 (Tisnérat-Laborde et al 2013;Ayache et al 2017), which is consistent with the signature found in the OM for the nuclear period. As our results are slightly higher than the values of the surface ocean, another possible source of enriched DIC originating from the river plume is the impact of the nuclear power plants along the Rhône during the last 40 years.…”

“…This Δ 14 C OM result is probably linked to the deposition of enriched phytoplankton grown in marine surface waters during the nuclear period which is mineralized in the sediment and which transfers its isotopic signature to the pore water DIC. Evidence for this is the fact that the Δ 14 C values obtained in the NW Mediterranean Sea surface were around +90‰ in the 1970s and decreased to 60‰ in 2010 (Tisnérat-Laborde et al 2013; Ayache et al 2017), which is consistent with the signature found in the OM for the nuclear period. As our results are slightly higher than the values of the surface ocean, another possible source of enriched DIC originating from the river plume is the impact of the nuclear power plants along the Rhône during the last 40 years.…”

“…On the marine side, the DIC and consequently the marine OM, such as phytoplankton, showed a value of Δ 14 C = –50‰ to Δ 14 C = –60‰ due to the marine reservoir effect in this zone (Siani et al 2000; Tisnérat-Laborde et al 2013). Then, during the last 50 years, after the atmospheric nuclear bomb tests and the penetration of the bomb radiocarbon into the river and the ocean, enriched values were measured in the Mediterranean Sea surface waters with Δ 14 C = +90‰ around 1970 and a decrease to Δ 14 C = +60‰ in 2010 (Tisnérat-Laborde et al 2013; Ayache et al 2017). After 1980, nuclear energy developed in France.…”

Modeling the biogeochemical impact of atmospheric phosphate deposition from desert dust and combustion sources to the Mediterranean Sea

“…CC BY 4.0 License. 2016a), tritium-helium-3 (Ayache et al, 2015) and 14 C (Ayache et al, 2016b). These evaluations 95…”