Plutonium isotopes in the NW Pacific: besides the global fallout

Due to the application potential for tracing oceanographic processes, the study on the distribution and geochemical behavior of Pu isotopes is of increasing interest to the scientific community of marine science. General excess inventories of Pu over those expected from global fallout in sediments and water column in the NW Pacific have been observed through the studies conducted in the 1970s-1990s. It has been speculated that the main source of these excess inventories could be the close-in and tropospheric fallout derived from large scale nuclear explosions at the Pacific Proving Ground (mainly on Bikini and Enewetok atolls) in the 1950s. In order to identify the source of Pu in the NW Pacific, we made a systematic investigation on the distribution of Pu isotopes in sediments, seawater and settling particles. Based on the obtained 240Pu/239Pu isotopic signature, we identified the wide presence of Bikini close-in fallout Pu in the studied regions. In this paper, we will discuss the possible oceanic process for the transport and scavenging of Bikini close-in fallout Pu containing particles, and evaluate the relative contribution of Pu between the global fallout and close-in fallout. Considerations on the future study of the distribution of Pu isotopes in the Southern Ocean within the framework of GEOTRACES Project will be presented.American Geophysical Union 2006 Western Pacific Geophysics Meetin