The triple disaster that began on March 11, 2011 in the Tohoku region of Japan started with an offshore magnitude 9.0 earthquake that triggered a devastating tsunami, leading to power losses, overheating and subsequent release of unprecedented amounts of radioactive materials to the oceans from the Fukushima Daiichi Nuclear Power Plant (FDNPP). It has been estimated that ＞80% of the total radioactivity releases entered the ocean either as atmospheric fallout or the direct discharge of contaminated waters. In order to study behavior of particulate radiocesium, we started time-series sediment trap experiment at station F1 about 100 km SSE-word from FDNPP.
