In 2017, in the Bering Sea and the Chukchi Sea on the edge of the Arctic Ocean that crossed the Bering Strait, cesium-137 originating from the Fukushima nuclear accident was detected. What was detected was a small amount, which was significantly lower than the standard value, but Qingshan said, “Considering from the trend, it should have expanded to the northern Arctic Ocean.”
Qingshan collected surface water at 761 in the North Pacific to investigate the activity of cesium-137 and cesium-134. Collecting observational data such as joint research and monitoring by governments of various countries, and using model calculations to analyze trends. Find out the route back to Japan around the southern side of the North Pacific, and the route from the Sea of Japan through the Tsugaru Strait back to the Pacific.
In this analysis, some of the cesium-137 reached the west coast of the United States and went northward. Flowing along the Alaska Peninsula, the activity measured in the Bering Sea in 2017 was 0.003 becquerels per liter of sea water and 0.004 becquerels in the Chukchi Sea.
On the northeastern coast of Japan, activity began to rise around 2018 and exceeded 0.002 becquerels in 2019. In the Tsugaru Strait, which crosses from the Sea of Japan to the Pacific side, the activity of cesium-137 reached its peak around 2017 and has since decreased.
Therefore, Aoyama analyzed that it was the cesium-137 that returned southward from the Bering Sea along the Kamchatka Peninsula. He said that through this research, “the cesium that originated from the accident at the Fukushima Daiichi nuclear power plant has identified major trends in the entire North Pacific over the past ten years.”