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    Alexandra Bruce
    February 20, 2013

    Just in case folks on the West Coast of North America were wondering how the Fukushima disaster may be affecting your habitat over the next 10 years, here is a computer simulation, produced by the Heimholtz Center for Oceanographic Research in Germany.

    It’s bad — but still not as bad as the present-day levels of radioactivity in the Baltic Sea, 36 years after the Chernobyl disaster…


    “Fukushima – Where is the Radioactive Water?”
    July 6, 2012

    Scientists at the GEOMAR | Helmholtz Center for Ocean Research have examined the long-term spread with the help of a model study. The strong mixing by oceanic eddy provides for rapid dilution of the radioactive water. The first landfall to be reached should be in about three years along the North American coast. The radioactivity should be already below the levels that are still to be found in the Baltic Sea, as a result of the Chernobyl disaster.

    During the nuclear disaster at Fukushima in March 2011, large amounts of radioactive material were released. A major part of it came through the atmosphere but also partly due to direct discharge into the Pacific Ocean, including long-lived isotopes in the seawater, as well soluble cesium-137.

    Using detailed computer simulations, researchers at GEOMAR | Helmholtz Centre for Ocean Research have studied the long-term propagation of radioactive water. “In our models, we have placed great emphasis on a realistic representation and fine details of the flow,” said the team leader, Prof. Claus Boning, “because the fabric spread not only by the mainstream, the Kuroshio, but mainly by intensive and highly variable vortex dominated areas.”

    “According to our model, it’s likely radioactive water had been distributed already to nearly half the North Pacific Ocean, due to strong turbulence in that area,” explained graduate oceanographer Erik Behrens, lead author of the published paper in the international journal “Environmental Research Letters” study. “In addition, winter storms have mixed the water into depths of around 500 meters.” The consequent dilution in the model calculation provides for a rapid decrease in cesium concentrations.

    The effect of the wide ocean mixing is particularly evident when comparing the model simulated the timing of the radiation levels in the Pacific with the situation in the Baltic Sea. “In March and April 2011, the water flowed into the Pacific, at the amount of radioactivity at least three times as large as the one that was registered in 1986 as a result of the Chernobyl disaster in the Baltic Sea,” said Boening. “Nevertheless, we simulated the radiation levels in the Pacific are already lower than the values ​​that can be found today, 26 years after Chernobyl, in the Baltic Sea.”

    According to the simulation model, the first landfalls of the contaminated water should occur around the autumn of 2013, along the strip the Hawaiian Islands and reach the North American coast around two to three years later.

    Unlike at the sea surface floating debris, which are distributed by the wind, the radioactive water is transported only by the currents below the sea surface. The other accompanying dilution will significantly slow now, since the oceanic eddies are much weaker than in the Kuroshio region in the eastern Pacific. Therefore, for years to come, the radiation levels in the North Pacific will be considerably higher than before the disaster.

    We would be very interested in contacting Claus Boning because his team has direct comparative measurements. “Then we could see immediately whether we are right, even if the absolute values ​​of the concentrations,” says Prof. Böning. Such data are for the Kiel scientists but not currently available.

    Original work:
    Behrens, E., f.u. Schwarzkopf, J.F. Lübbecke and C.W. Böning, 2012: Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima. Environmental Research Letters, 7,

    High resolution image:

    Simulated expansion of the contaminated Wasses the summer of 2012, 16 months after the nuclear disaster. The colors illustrate the dilution relative to the original starting concentration in the Japanese coastal waters: the highest values ​​(colored red) have amounted to about one-thousandth of the value in April 2011. Source: GEOMAR.

    Animation of the spread of the contaminated water. Video sequence of the time course over a period of 10 years after the nuclear disaster. The colors illustrate the dilution relative to the original concentration in the Japanese coastal waters. Source: GEOMAR.

    Prof. Dr. Claus Böning (theory and modeling, GEOMAR), tel 600-4003 0431,
    Jan Steffen (GEOMAR, Communication & Media), Tel: 0431 600-2811,


    July 23, 2012

    Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima Published 7/9, 2012.

    (English explanation)

    *Erik Behrens et al 2012 Environ. Res. Lett. 7 034004

    *GEOMAR | Helmholtz Centre for Ocean Research, Kiel


    *Video sequence of the time course over a period of 10 years after Fukushima Nuclear disaster.The colors illustrate the dilution relative to the initial concentration in the Japanese coastal waters.

    *A sequence of global ocean circulation models, with horizontal mesh sizes of 0.5°, 0.25° and 0.1°, are used to estimate the long-term dispersion by ocean currents and mesoscale eddies of a slowly decaying tracer (half-life of 30 years, comparable to that of 137Cs) from the local waters off the Fukushima Dai-ichi Nuclear Power Plants. The tracer was continuously injected into the coastal waters over some weeks; its subsequent spreading and dilution in the Pacific Ocean was then simulated for 10 years. The simulations do not include any data assimilation, and thus, do not account for the actual state of the local ocean currents during the release of highly contaminated water from the damaged plants in March–April 2011. An ensemble differing in initial current distributions illustrates their importance for the tracer patterns evolving during the first months, but suggests a minor relevance for the large-scale tracer distributions after 2-3 years. By then the tracer cloud has penetrated to depths of more than 400 m, spanning the western and central North Pacific between 25°N and 55°N, leading to a rapid dilution of concentrations.

    **To be Continued ⇒



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    Alexandra Bruce

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