Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, NS, Canada B2Y 4A2;
Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada V8L 4B2; and.
Proc Natl Acad Sci U S A. 2015 Feb 3;112(5):1310-5. doi: 10.1073/pnas.1412814112. Epub 2014 Dec 29.
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.
2011 年福岛第一核电站事故向西北太平洋大量释放放射性物质，引发了人们对这些物质跨越大洋传播到北美的广泛关注。我们在此报告了首次对福岛放射性物质信号传播到北太平洋东部的系统研究。通过对海水中 (134)Cs 和 (137)Cs 的时间序列测量，我们发现福岛信号于 2012 年 6 月通过海流传输到达了加拿大不列颠哥伦比亚以西 1500 公里处的位置，这距离事故发生大约 1.3 年。到 2013 年 6 月，福岛信号已经扩散到加拿大大陆架，到 2014 年 2 月，福岛信号在整个水柱的上层 150 米范围内增加到 2 Bq/m(3)，导致大气核武器试验沉降背景的放射性活度增加了一倍。与我们的测量值相当吻合的海洋环流模型估计表明，到 2015-2016 年，北美的福岛放射性物质（福岛衍生的 (137)Cs 和沉降 (137)Cs）的总水平将可能达到 3-5 Bq/m(3)的最大值，然后到 2021 年下降到更接近沉降背景的约 1 Bq/m(3)的水平。来自福岛输入的北太平洋东部 (137)Cs 水平的增加可能会使该地区的浓度恢复到 20 世纪 80 年代盛行的沉降水平，但不会对人类健康或环境构成威胁。
