Seawater and plankton: 134Cs and 137Cs in the seawater around Japan and in the North Pacific

Abstract

Enormous quantities of radionuclides were released into the ocean viaboth atmospheric deposition and direct release as a result of the Fukushima Dai-ichiNuclear Power Plant (FNPP) accident. The evaluation of FNPP-derived radioactivecesium (Cs) in the marine environment is important in addressing risks to bothmarine ecosystems and public health through consumption of fisheries products.Understanding the distribution patterns of radioactive Cs in the ocean throughoutthe water column is key in assessing its effects on marine ecosystems. This chaptersummarizes the dispersion pattern of FNPP-derived radioactive Cs in the NorthPacific and around Japan, based on our observational studies as follows: (1) eastwarddispersion in surface seawater; (2) southwestward intrusion with mode water;and (3) background level 137Cs without any detectable 134Cs in the Japan Sea, EastChina Sea, Seto Inland Sea, and Bering Sea, along with highly radioactive Cs off thecoast of East Japan.