Fukushima-derived radiocesium in the western North Pacific in 2014

In 2014, we measured activity concentration of radiocesium in the western North Pacific Ocean. In the north of Kuroshio Front high activity concentration of Fukushima-derived radiocesium in surface mixed layerin 2012 had been transported eastward by 2014. In the south of the front we found a radiocesium subsurface maximum in 200–600 m depth, which was similar to that observed in 2012. The subsurface maximum spread southward from 18°N to 15°N between 2012 and 2014, which suggests spreading of Fukushima-derived radiocesium into the whole western subtropicalarea by 2014 due to formation and subduction of the subtropical mode water.