Radiation Levels Will Concentrate in Pockets In Baja California and Other West Coast Locations

Washington’s Blog
August 21, 2013

An ocean current called the North Pacific Gyre is bringing Japanese radiation to the West Coast of North America:

While many people assume that the ocean will dilute the Fukushima radiation, a previously-secret 1955 U.S. government report concluded that the ocean may not adequately dilute radiation from nuclear accidents, and there could be “pockets” and “streams” of highly-concentrated radiation.

The University of Hawaii’s International Pacific Research Center created a graphic showing the projected dispersion of debris from Japan:

Last year, scientists from the National Oceanic and Atmospheric Administration’s (NOAA) Pacific Marine Environmental Laboratory and 3 scientists from the GEOMAR Research Center for Marine Geosciences showed that radiation on the West Coast of North America could end up being 10 times higher than in Japan:

After 10 years the concentrations become nearly homogeneous over the whole Pacific, with higher values in the east, extending along the North American coast with a maximum (~1 × 10−4) off Baja California. 

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With caution given to the various idealizations (unknown actual oceanic state during release, unknown release area, no biological effects included, see section 3.4), the following conclusions may be drawn. (i) Dilution due to swift horizontal and vertical dispersion in the vicinity of the energetic Kuroshio regime leads to a rapid decrease of radioactivity levels during the first 2 years, with a decline of near-surface peak concentrations to values around 10 Bq m−3 (based on a total input of 10 PBq). The strong lateral dispersion, related to the vigorous eddy fields in the mid-latitude western Pacific, appears significantly under-estimated in the non-eddying (0.5°) model version. (ii) The subsequent pace of dilution is strongly reduced, owing to the eastward advection of the main tracer cloud towards the much less energetic areas of the central and eastern North Pacific. (iii) The magnitude of additional peak radioactivity should drop to values comparable to the pre-Fukushima levels after 6–9 years (i.e. total peak concentrations would then have declined below twice pre-Fukushima levels). (iv) By then the tracer cloud will span almost the entire North Pacific, with peak concentrations off the North American coast an order-of-magnitude higher than in the western Pacific.

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