The Meteorological Research Institute published their analysis data showing radiation from the ruined Fukushima reactors and spent fuel pools went around the earth within 10 days, and that 70 ~ 80 % of radioactive cesium dropped into the Pacific Ocean by April.
Mr.Tanaka, a member of the team said, from March to April, subtropical westerlies conveyed most of the plume out of the Japanese islands, but most of it had dropped and contaminated the Pacific Ocean.
(Source)