Plankton and seawater sampled at 10 points less than a year after the Fukushima meltdowns found concentrations of radioactive cesium were highest at different locations in the Pacific, puzzling scientists.

The group collected zooplankton and surface seawater at 10 points between Hokkaido and Guam, 500 to 2,100 km from the crippled power plant, between Jan. 14 and Feb. 5, 2012.

Cesium 134, with a half-life of two years, and cesium 137, with a half-life of 30 years, were detected in plankton and seawater at all 10 locations, according to their report. Plankton with the highest concentrations of cesium 134, at 10.5 becquerels per kilogram, and cesium 137, at 14.9 becquerels, were found around 25 degrees north latitude and 150 degrees east longitude, the report said. The samples were taken from the surface to a depth of 200 meters.