Spatial distributions of 137Cs and plutonium in the Pacific: Results of BEAGLE2003 cruise

Abstract

¹³⁷Cs and plutonium in the ocean were mainly injected by global fallout due to the large-scale atmospheric nuclear testing. Temporal and spatial variations of ¹³⁷Cs and plutonium concentrations are important not only as aspect of assessment of radiological effect but also as better understanding of oceanic processes. In 2003/4, BEAGLE2003 expedition, around the globe along about 30 deg.S latitude, was conducted using R/V "MIRAI" by JAMSTEC. We have collected about 800 water samples to determine anthropogenic radionuclides. Therefore we can depict the first detail distributions of ¹³⁷Cs and plutonium in the South Pacific. ¹³⁷Cs concentrations in the South Pacific surface waters ranged from 0.1 to 1.5 Bq m^-3. The ¹³⁷Cs concentrations in the central subtropical South Pacific are the same as that in the subtropical North Pacific, whereas extremely low ¹³⁷Cs concentrations were observed at stations near the South America. ^239,240Pu concentrations in the South Pacific surface waters ranged from 0.5 to 4.1 mBq m^-3, which are the same or slightly lower than that in the subtropical North Pacific.