Abstract
Vertical distributions of 239+240Pu activity and 240Pu/239Pu atom ratio in settling particles and the particulate 239+240Pu fluxes in the water column in the western Northwest Pacific were investigated. Time-series settling particle samples were collected using sediment traps to examine the seasonal variation of Pu flux and 240Pu/239Pu atom ratio. The high (> 0.18) 240Pu/239Pu atom ratios in settling particles indicate that plutonium from the Pacific Proving Grounds (PPG) source in the central Pacific is transported toward the western Northwest Pacific. Evidence indicates that Pu scavenging onto the settling particles is strongly dependent upon the bulk mass flux. The results suggest that advective lateral transport of dissolved Pu from the open ocean to the ocean margin and removal of Pu into the margin sediments by particle scavenging is a common phenomenon in the Pacific Ocean.
