Host phases of fallout239,240Pu and241Am were studied in the surface sediments obtained in 1994 from abyssal basins of relatively small area of the western North
Pacific. An analytical procedure involving sequential chemical extraction was employed for partitioning the host phases of
the nuclides in sediment into five fractions: (1) exchangeable (2) bound to carbonate, (3) bound to hydrous Fe-Mn oxides,
(4) bound to organic matter and (5) residual. Decrease of total239,240Pu concentration with decreasing association of239,240Pu with organic matter, high241Am/239,240Pu activity ratio in carbonate phase and somewhat high proportion of oxidized239,240Pu in leachable phases suggest a possibility of post-depositional diagenetic remobilization of Pu from sediment to water column.