Plutonium Isotopes in Settling Particles: Transport and Scavenging of Pu in the Western Northwest Pacific

We examined the vertical distributions of 239+240Pu activity and 240Pu/239Pu atom ratio in settling particles and quantified the particulate 239+240Pu fluxes in the water column in the western Northwest Pacific. Settling particle samples were collected using sediment traps. Plutonium isotopes were analyzed using a sector field high-resolution ICP-MS. To the best of our knowledge, this is the first time that both Pu activity and Pu isotope ratio data have been obtained for settling particles in the Pacific Ocean. 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. Plutonium can be considered as a useful tracer to study the transport and fate of other contaminants that readily adsorb to particles in marine environments

Sediment Core Record of Global Fallout and Bikini Close-in Fallout Pu in Sagami Bay, Western Northwest Pacific Margin

The total 239+240Pu activity and 240Pu/239Pu atom ratio in the sediments in Sagami Bay of the western Northwest Pacific margin were investigated using ICP-MS with a shield torch system. 239+240Pu inventories in the examined sediment cores were found to be much higher than those predicted from atmospheric global fallout (42 MBq/km2) at the same latitude. In addition, elevated 240Pu/239Pu atom ratios ranging from 0.22 to 0.28 were observed in the sediment samples. On the basis of the vertical profiles of239+240Pu and characterized 240Pu/239Pu atom ratios in a sediment core collected in the center of Sagami Bay, we identified two distinct sources of fallout Pu in the bay:  the global stratospheric fallout with characteristic240Pu/239Pu ratio of 0.18 and the transported close-in fallout derived from Bikini and Enewetak surface nuclear weapon test series in the 1950s. We propose that the Pu transportation was mainly due to oceanic processes (for example, through the North Equatorial Current and the Kuroshio Current). Using a two fallout end-member model, we find that the contribution of Bikini close-in fallout Pu ranged from 44 to 59% in Sagami Bay sediments. To the best of our knowledge, this is the first report that Pu contamination, which originated from Bikini and Enewetak nuclear weapon test series in the 1950s, has extended westwards as far as the Japanese coast

PSO-LSSVM training and testing data.

The training and testing data in the file can be used to train the PSO-LSSVM to obtain CRI and plot the results as shown in Figs 7 and 8. (XLSX)</p

The main parameters in this paper.

The main parameters in this paper.</p

Online rolling identification results of the ship domain.

(T1) Identification results at Time T1, correspondingly, ; (T2) Identification results at time T2, correspondingly, ; (T3) Identification results at time T3, correspondingly, ; (T4) Identification results at time T4, correspondingly, ; (T5) Identification results at Time T5, correspondingly, ; (T6) Identification results at Time T6, correspondingly, .</p

Online identification outbound or inbound process data.

The own ship’s trajectory can be plotted using the position data, as shown in Fig 6. The outbound data in Excel can be used for rolling online recognition, and the results can be obtained as shown in Figs 9 to 12. Meanwhile, the inbound data in Excel can be used for rolling online recognition, and the results can be obtained as shown in Figs 13 to 16. (XLSX)</p

Fitness curve during training.

Fitness curve during training.</p

AIS track of ships entering and leaving ports.

AIS track of ships entering and leaving ports.</p

Online rolling identification results of the ship domain.

(T1) Identification results at Time T1, correspondingly, ; (T2) Identification results at time T2, correspondingly, ; (T3) Identification results at time T3, correspondingly, ; (T4) Identification results at time T4, correspondingly, ; (T5) Identification results at Time T5, correspondingly, ; (T6) Identification results at Time T6, correspondingly, .</p

Schematic diagram of the CRI model based on the LSSVM.

Schematic diagram of the CRI model based on the LSSVM.</p