Plutonium-239 has been found in over-ocean aerosols in about the same ratio to Strontium-90 as that reported over land. In seawater, Pu-239:Sr-90 ratios are shown to be less than half of those in over-ocean aerosols, confirming geochemical separation of these nuclides in the ocean. It is suggested that the sedimentation of Pu-239 may be more involved with biological processes than has been found for Ce-144 or Pm-147.
Bowen, V. T., K. M. Wong, and V. E. Noshkin. 1971. "Plutonium-239 in and over the Atlantic Ocean." Journal of Marine Research 29, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1197