Transport of radionuclides near the seabed off Fukushima; Finding from AMS measurements

Otosaka, Shigeyoshi  

Cesium and iodine are known to behave differently in the marine environment. However, in 2011, activity ratio of I/Cs in seabed sediment collected in the 160 km radius from the Fukushima Daiichi Nuclear Power Plant showed almost constant regardless of observation areas. This result indicated that initial deposition of I and Cs to the seafloor was not caused by gentle settling of biogenic particles, but by the contact of highly-contaminated seawater with the seafloor in a relatively short period of time. After that, the I/Cs ratio decreased in the coast and slightly increased in the offshore (water depth of 200 m to 500 m) regions. Such changes in the I/Cs ratio provide helpful information showing the transport of radionuclides near the seabed at the scale of several years.