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Abstract: Vertical profiles of dissolved plutonium activity concentration in South Pacific Ocean water columns were determined using ICP-SF-MS after Fe co-precipitation and radiochemical purification. The water samples were collected in the central South Pacific mid-latitude region (32.5°S) during the BEAGLE2003 expedition conducted in 2003–2004 by the Japan Agency for Marine-Earth Science and Technology. 239Pu concentrations in surface water were around 1mBqm−3. Concentrations reached a maximum (6mBqm−3) at 600–800m, and then decreased with increasing depth. The vertical profile pattern was similar to that observed in the North Pacific subtropical gyre, although concentrations of 239Pu in the deep South Pacific were significantly lower than those in the North Pacific subtropical gyre. The 239Pu/137Cs activity ratios, which reflect biogeochemical processes in seawater, increased exponentially from the surface to 1500m depth, whereas in deep waters they were almost constant. The estimated 239,240Pu inventories in the South Pacific water column (0–2300m) were of the same order of magnitude as previous estimates in 1996 (15°S, 148°W); however they were about one order of magnitude lower than those in the western North Pacific. [Copyright &y& Elsevier]

Abstract: The distribution of 239Pu in Atlantic and Indian Ocean waters about four decades after their main injection from atmospheric nuclear weapons tests is discussed. Recent data obtained in the framework of the SHOTS (Southern Hemisphere Ocean Tracer Studies) projects are evaluated and compared with previous investigations. Seawater samples were collected during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) along the 30°S transect in the Atlantic and the 20°S transect in the Indian Ocean. The results indicate transport of surface waters labelled with 239Pu from the western North Pacific via the Indonesian Seas to the South Indian Ocean and then to the South Atlantic Ocean. Along the whole BEAGLE2003 sampling route, the Atlantic Ocean has the lowest 239Pu content due to its particle scavenging on the long way from the western North Pacific. On the other hand, concentrations of the conservative 137Cs tracer are in all three oceanic basins comparable. The primary productivity reflected by the chlorophyll content in surface waters has similar longitudinal distribution as 239Pu. Radioactive and chlorophyll tracers revealed that the most important current system in each southern oceanic basin is represented by the Subtropical gyre. While the main streams of the gyres maintain high concentrations of tracers, inside the loops the tracer concentrations are the lowest. [Copyright &y& Elsevier]

Abstract: The measurement of plutonium isotopes, 239Pu and 240Pu, at 670kV on the compact accelerator mass spectrometry (AMS) system at the Centro Nacional de Aceleradores (CNA) in Seville, Spain, is now a reality. In this work, we present first Pu AMS results for environmental samples: a sediment core collected in a submarine canyon in the Mediterranean coast of the Spanish region of Palomares, affected by a nuclear accident in 1966. From the study of the 240Pu/239Pu atomic ratio profile, showing on average levels lower than 11%, we confirm that the weapon-grade plutonium released on land during the accident, with a characteristic 240Pu/239Pu atomic ratio of 5.8%, has found its way into the marine environment. A two-plutonium sources mixture model (Palomares and fallout) is used to elucidate the percentage of the plutonium coming from the accident. As a validation exercise of the Pu AMS measuring technique and in order to obtain the 238Pu/(239+240)Pu activity ratios, samples were also studied by alpha-spectrometry (AS). The obtained AS 239+240Pu activity concentration results fit in with the AMS ones in a wide dynamic range, thus validating the AMS technique. [Copyright &y& Elsevier]

The present plutonium and 137Cs concentrations in South Pacific Ocean surface waters were determined. The water samples were collected in the South Pacific mid-latitude region (32.5 °S) during the BEAGLE expedition conducted in 2003–04 by JAMSTEC. 239,240Pu concentrations in surface seawater of the South Pacific were in the range of 0.5 to 4.1 mBq m−3, whereas 137Cs concentrations ranged from 0.07 to 1.7 Bq m−3. The observed 239,240Pu and 137Cs concentrations in the South Pacific were almost of the same level as those in the North Pacific subtropical gyre. The surface 239,240Pu in the South Pacific subtropical gyre showed larger spatial variations than 137Cs, as it may be affected by physical and biogeochemical processes. The 239,240Pu/137Cs activity ratios, which reflect biogeochemical processes in seawater, were generally smaller than that observed in global fallout, except for the most eastern station. The 239,240Pu/137Cs ratios in the South Pacific tend to be higher than that in the North Pacific. The relationships between anthropogenic radionuclides and oceanographic parameters such as salinity and nutrients were examined. The 137Cs concentrations in the western South Pacific (the Tasman Sea) and the eastern South Pacific were negatively correlated with the phosphate concentration, whereas there is no correlation between the 137Cs and nutrients concentrations in the South Pacific subtropical gyre. The mutual relationships between anthropogenic radionuclides and oceanographic parameters are important for better understanding of transport processes of anthropogenic radionuclides and their fate in the South Pacific. [Copyright &y& Elsevier]