title: Arrival of the Fukushima radioactivity plume in North American continental waters.
abstract: The large discharge of radioactivity into the northwest Pacific Ocean from the 2011 Fukushima Dai-ichi nuclear reactor accident has generated considerable concern about the spread of this material across the ocean to North America. We report here the first systematic study to our knowledge of the transport of the Fukushima marine radioactivity signal to the eastern North Pacific. Time series measurements of (134)Cs and (137)Cs in seawater revealed the initial arrival of the Fukushima signal by ocean current transport at a location 1,500 km west of British Columbia, Canada, in June 2012, about 1.3 y after the accident. By June 2013, the Fukushima signal had spread onto the Canadian continental shelf, and by February 2014, it had increased to a value of 2 Bq/m(3) throughout the upper 150 m of the water column, resulting in an overall doubling of the fallout background from atmospheric nuclear weapons tests. Ocean circulation model estimates that are in reasonable agreement with our measured values indicate that future total levels of (137)Cs (Fukushima-derived plus fallout (137)Cs) off the North American coast will likely attain maximum values in the 3-5 Bq/m(3) range by 2015-2016 before declining to levels closer to the fallout background of about 1 Bq/m(3) by 2021. The increase in (137)Cs levels in the eastern North Pacific from Fukushima inputs will probably return eastern North Pacific concentrations to the fallout levels that prevailed during the 1980s but does not represent a threat to human health or the environment.
authors.affiliation: Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada B2Y 4A2; john.smith@dfo-mpo.gc.ca.
authors.forename: John N
authors.initials: JN
authors.lastname: Smith
authors.affiliation: Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada V8L 4B2; and.
authors.forename: Robin M
authors.initials: RM
authors.lastname: Brown
authors.affiliation: Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada V8L 4B2; and.
authors.forename: William J
authors.initials: WJ
authors.lastname: Williams
authors.affiliation: Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada V8L 4B2; and.
authors.forename: Marie
authors.initials: M
authors.lastname: Robert
authors.affiliation: Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada B2Y 4A2;
authors.forename: Richard
authors.initials: R
authors.lastname: Nelson
authors.affiliation: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197.
authors.forename: S Bradley
authors.initials: SB
authors.lastname: Moran
keywords: 137Cs; Fukushima; oceanography; tracer