Complexation-scavenging of plutonium in the ocean

In order to understand vertical profiles of 239,240Pu in open ocean water columns, a simple scavenging model is introduced. The model includes chemical and biogeochemical processes: one is the organic complexation of 239,240Pu with binding sites in sinking particles, and the other the export flux of particulate organic matter (POM). The complexation-scavenging model provides a simple relationship for the vertical flux of particle-reactive radionuclides such as 239,240Pu: i.e., the vertical transport rate constant is expressed as a product between the partition coefficient of a particle-reactive radionuclide and the export flux of POM. A time-dependent five-layer model was developed based on the complexation scavenging. The model can successively reproduce time-dependent vertical profiles of 239,240Pu in the North Pacific, especially with a mid-depth maximum; a maximum concentration of 239,240Pu in the water column occurs in the first layer (0-100 m) until 1968, the 239,240Pu maximum moves downward in the second layer (100-270 m) in 1969, and in 1976, the 239,240Pu maximum appears in the third layer (270-641 m). (author)