Transport processes of particulate materials near the seabed off Fukushima inferred from I/Cs ratio in sediment

Otosaka, Shigeyoshi  ; Sato, Yuhi; Suzuki, Takashi  ; Kuwabara, Jun 

Transport processes of radionuclides derived from the accident of Fukushima Daiichi Nuclear Power Plant (FDNPP) near the seabed are inferred from relationship between I and Cs concentrations in seabed sediment collected from August 2011 to January 2013 at totally 24 stations. I and Cs concentrations in the sediment surface (01 cm layer) were 0.040.45 mBq/kg and 12230 Bq/kg, respectively. The I/Cs ratio generally increased with time and the increasing tendency was remarkable in the shelf break region (bottom depth: 200400 m). These results indicate that (1) particles with higher I and Cs ratio settled to the bottom layer after 2012, and (2) such "recently settled" particles were accumulated in the shelf break region. The I/Cs in seabed sediment would be a helpful indicator to trace the fate of particulate radionuclides from coast to the open ocean.