Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-OS Ocean Sciences & Ocean Environment

[A-OS13] Ocean circulation and material cycle in coastal seas

Mon. May 27, 2019 1:45 PM - 3:15 PM 102 (1F)

convener:Kiyoshi Tanaka(University of Tokyo), Akihiko Morimoto(Ehime University), Yuichi Hayami(Saga University), Kazuhiko Ichimi(Seto Inland Sea Regional Research Center, Kagawa University), Chairperson:Akihiko Morimoto, Yuichi Hayami

2:45 PM - 3:00 PM

[AOS13-11] Spreading of Radioactive Cesium off Joban coast through Large River Discharge

*Kiyoshi Tanaka1, Seiya Nagao2, Yujiro Kitade3, Masato Niki4, Takaaki Katsumata4, Toru Miyama5 (1.University of Tokyo, 2.Kanazawa University, 3.Tokyo University of Marine Science and Technology, 4.Tokai University, 5.Japan Agency for Marine-Earth Science and Technology)

Keywords:radioactive cesium, river discharge, 2011 Great East Japan Earthquake, off the Joban coast

A hydrographic observation was conducted off the Joban coast during September 7 to 12, 2011 (six months after the 2011 Great East Japan Earthquake), using a CTD profiler and a ship-mounted ADCP (R/V Tansei-Maru cruise KT-11-22). At the same time, water-samplings for radioactive cesium measurements were conducted at a depth of 10 m. The radioactivity of cesium (134Cs and 137Cs) was measured for the AMP/Cs compound using gamma-ray spectrometry at the Low Level Radioactivity Laboratory of Kanazawa University. There was a negative correlation between the radioactive cesium and salinity in the sea surface (at the depth of 10 m), indicating more radioactive cesium was included in less saline water. Abundant freshwater is discharged from three large rivers (Tone, Naka, and Kuji Rivers) into the observational area. What is important is that several days before the observation, there was extremely heavy rainfall in the upper reaches of the rivers, which resulted in that discharge of the Tone River exceeded 2000 m3/s on September 4. Therefore, it was suggested that the highly concentrated radioactive cesium in the sea surface originated from the land through the rivers. Moreover, it was shown that spreading of the river water and radioactive cesium is strongly influenced by the Kuroshio Current.