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Supplementary document
The Japan Sea Expeditions by JAEA (1) Importance and progress of the Japan Sea expeditions The Japan Sea is a semi-closed marginal sea separated from the North Pacific by shallow sills. Because of its bowl-like topography and unique seawater circulation, the Japan Sea is used as a “miniature” of the ocean to assess influences of global climate change on the marine environment. In addition, understanding the radioecological processes in the Japan Sea is important in assessing the safety of marine resources because of the many nuclear facilities in the region surrounding the Japan Sea. The Japan Sea expeditions by JAEA started with the first and second Japanese-Korean-Russian joint expeditions in 1994 and 1995. The purpose of these expeditions was to investigate the status of radiological consequences of radioactive waste dumped in the Japan Sea and its surrounding regions. Anthropogenic radionuclides were detected in samples of seawater and seabed sediments collected in the dumping areas, but no significant difference in concentrations was observed, compared with the data in the corresponding background areas and the data of previous observations before 1986 when a large quantity of radioactive waste was dumped in the Japan Sea. Radionuclides detected in the dumping areas are concluded to have resulted from global fallout due to  Figure 1. Sampling stations in the Japan Sea visited by JAEA (Stations of the Japanese-Korean-Russian joint expeditions are not included.)
atmospheric nuclear weapons testing. The radiological consequences of these radionuclides on human physiology were negligible. So far there have been no indications of radiological consequence due to dumping on the marine environment. Using its Mutsu Establishment as a research base, JAEA has since continued the expeditions in the Russian EEZ to clarify seawater circulation and transport processes of materials in the Japan Sea, in cooperation with the Far Eastern Regional Hydrometeorological Research Institute (FERHRI) under the International Science and Technology Center (ISTC) partner project. The ISTC expedition was the only one to investigate recently the distribution of radionuclides in the Russian EEZ by Japanese researchers. At the same time as the ISTC project, JAEA observed the Japanese EEZ under entrusted research by the Science and Technology Agency/the Ministry of Education, Culture, Sports, Science and Technology of Japan (STA/MEXT) and cooperative research with Hokkaido University and Kyusyu University. During the expeditions, oceanographic data such as temperature, salinity, and current speed and direction were obtained, and samples of seawater, seabed sediments, and settling particles for radiochemical analysis were collected. Throughout the expeditions, JAEA succeeded in covering almost all areas of the Japan Sea that could be observed at present (Figure 1). (2) Methods for oceanographic observations in the Japan Sea
(3) Future research At the Mutsu Establishment of JAEA, an accelerator mass spectrometer (AMS; see Figure 4) continues to measure radiocarbon (14C) in dissolved inorganic carbon of seawater collected during the above expeditions. The results of these measurements will enable determining the structure of water masses and long-term processes of seawater circulation in the Japan Sea. JAEA plans to continue observations in the Japan Sea using opportunities for cooperative research with other institutes and the ISTC regular project, as well as JAEA's original expeditions. Further expeditions will investigate regions where observations have not yet been carried out, and clarify the seasonal variations of the transport processes of materials in the Japan Sea. Developing a model for predicting the transfer of materials in the Japan Sea is the main subject of the current medium-term plan for JAEA's environmental research. Findings and results obtained from previous and further expeditions in the Japan Sea are expected to be available for developing and validating a marine environmental assessment system consisting of a water circulation model and a material transfer model.  Figure 4. Accelerator mass spectrometer installed at JAEA-Mutsu |
