Bomb radiocarbon invasion into the northwestern North Pacific

Invasion of the bomb radiocarbon was investigated in the northwestern North Pacific, including the subarctic (Oyashio region), the subtropical (Kuroshio region), and the subarctic/subtropical mixing (transition) areas. After the GEOSECS Pacific expedition in 1973, the bomb radiocarbon decreased in the Oyashio region and increased in the Kuroshio region. The former was caused by rapid ventilation of the Oyashio water. The latter was owing to accumulation of the bomb radiocarbon in the intermediate water of the Kuroshio region. The reverse trends in the temporal variation of radiocarbon between the Oyashio and the Kuroshio regions lead to virtually small temporal change of the bomb radiocarbon in the transition area where the two waters mix. The temporal changes of the bomb radiocarbon suggest that the North Pacific Intermediate Water is formed in the northwestern North Pacific.