Simulating transport of non-Chernobyl 137Cs and 90Sr in the North Atlantic–Arctic region

Abstract

The spatial and temporal distributions of the anthropogenic radionuclides 137 Cs and 90 Sr, originating from nuclear bomb testing and the Sellafield reprocessing plants in the Irish Sea, are simulated using a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The physical model is forced with daily atmospheric re-analysed fields for the period 1950 to present. Comparison of temporal evolution of observed and simulated concentrations of 137 Cs have been conducted for the regions east of Scotland, west of central Norway and at the entrance of the Barents Sea. It follows that the radionuclides from the Sellafield discharge reach the Barents Sea region after 4-5 years, in accordance with observations. The simulation provides a detailed distribution and evolution of the radionuclides over the integration time. For the Atlantic waters off the coast of Norway and in the southern Barents Sea, the atmospheric fallout dominates over the Sellafield release up to the mid 1960s and from the early 1990s, whereas Sellafield is the main source for the two radionuclides in the 1970s and 1980s. It is furthermore argued that model systems like the one presented here can be used for future prediction of radioactive contaminations in the Nordic Seas and the Arctic Ocean, for instance under various global warming scenarios.

Tracer-derived transit time of the waters in the eastern Nordic Seas

“…3). The obtained transit times are in accordance with earlier observation-based studies (Kershaw and Baxter, 1995;Livingston et al, 1984), as well as model studies (Nies et al, 1998;Gao et al, 2004;Karcher et al, 2004). Furthermore, Brown et al (2002) found that the transit time is 3.5 yr (42 months) for the Sellafield signal to reach the northern coast of Norway based on cross-correlation analysis of observed 99 Tc in the 1990s.…”

“…for the northern North Atlantic and the Nordic Seas, will not be given here as these quantities have been addressed in the studies of Furevik et al (2002), Gao et al (2003Gao et al ( , 2004, Nilsen et al (2003), Hatun et al (2005) and Eldevik et al (2005) for model systems closely related to the one used here. In general, the model system has demonstrated skill in simulating the ocean circulation and thermodynamics in the region of interest.…”

“…4 1995 (a) 1955 1960 1965 1970 1975 1980 1985 1990 1995 1955 1960 1965 1970 1975 1980 1985 1990 1995 Kershaw and Baxter (1995) in circles, the simulated surface concentration due to the atmospheric fallout (dashed line) and the sum of the concentrations from the Sellafield release and the atmospheric fallout (thick solid line) for the east of Scotland (a), west of Norway (b) and in the southwestern Barents Sea region (c). For comparison, the thin line corresponds to the thick solid line, but is taken from the 80 km resolution version of the model (Gao et al, 2004). Note the different concentration scales on the panels.…”

“…For instance, radionuclides from the atmospheric nuclear bomb tests in in the 1950s and 1960s and chlorofluorocarbons (CFCs) emitted to the atmosphere since the 1930s have been used to explore the regional to global decadal-scale ventilation of the ocean surface waters (England and Maier-Reimer, 2001; Aoyama and Hirose, 2003;Willey et al, 2004), whereas natural radiocarbon has been used to map the path and age of the global overturning circulation (Toggweiler et al, 1989a,b). Other radionuclides like caesium-137 ( 137 Cs), strontium-90 ( 90 Sr) and technetium-99 ( 99 Tc) originating from nuclear fuel reprocessing plants have been used to explore the local and basin-scale transport and dispersion of the waters exposed to these discharges (Dahlgaard, 1995;Brown et al, 2002;Gao et al, 2004;Karcher et al, 2004).…”

Diagnosing ocean tracer transport from Sellafield and Dounreay by equivalent diffusion and age

“…In a pioneering work by Prandle (1984), mixing and time-scales of the radionuclide 137 Cs on the European continental shelf was investigated. More recently, it has been shown that the current generation of OGCMs are capable of simulating the large-scale dispersion (Nordic Seas and the Arctic Ocean) of radionuclides from both European reprocessing plants and atmospheric fallout from nuclear bomb testing in a realistic manner (e.g., Karcher et al, 2004;Gao et al, 2004).…”