Transport of 137Cs And 239,240Pu with Ice-rafted Debris in the Arctic Ocean

Abstract

Ice rafting is the dominant mechanism responsible for the transport of fine-grained sediments from coastal zones to the deep Arctic Basin. Therefore, the drift of ice-rafted debris (IRD) could be a significant transport mechanism from the shelf to the deep basin for radionuclides originating from nuclear fuel cycle activities and released to coastal Arctic regions of the former Soviet Union.In this study, 28 samples of IRD collected from the Arctic ice pack during expeditions in 1989 -95 were analyzed for 137 Cs by gamma spectrometry and for 239 Pu and 240 Pu by thermal ionization mass spectrometry. 137 Cs concentrations in the IRD ranged from less than 0.2 to 78 Bq·kg -1 (dry weight basis). The two samples with the highest 137 Cs concentrations were collected in the vicinity of Franz Josef Land, and their backward trajectories suggest origins in the Kara Sea. Among the lowest 137 Cs values are seven measured on sediments entrained on the North American shelf in 1989 and 1995, and sampled on the shelf less than six months later.Concentrations of 239 Pu + 240 Pu ranged from about 0.02 to 1.8 Bq·kg -1 . The two highest values came from samples collected in the central Canada Basin and near Spitsbergen; calculated backward trajectories suggest at least 14 years of circulation in the Canada Basin in the former case, and an origin near Severnaya Zemlya (at the Kara Sea/Laptev Sea boundary) in the latter case. While most of the IRD samples showed 240 Pu/ 239 Pu ratios near the mean global fallout value of 0.185, five of the samples had lower ratios, in the 0.119 to 0.166 range, indicative of mixtures of Pu from fallout and from the reprocessing of weapons-grade Pu. The backward trajectories of these five samples suggest origins in the Kara Sea or near Severnaya Zemlya.RÉSUMÉ. Le transport glaciel constitue le principal mécanisme responsable du transport des sédiments à grain fin depuis les zones côtières jusqu'à la fosse du bassin Arctique. La dérive des débris du transport glaciel pourrait constituer un important mécanisme de transport, depuis la plate-forme continentale jusqu'à la fosse marine, pour des radionucléides provenant d'activités connexes au cycle du combustible nucléaire, radionucléides qui sont éliminés vers les zones côtières arctiques de l'ancienne Union Soviétique.Dans cette étude, on a analysé 28 échantillons de débris de transport glaciel recueillis dans la glace arctique au cours d'expéditions effectuées de 1989 à 1995, en vue d'y déceler du 137 Cs par spectrométrie gamma ainsi que du 239 Pu et du 240 Pu par spectrométrie de masse réalisée par thermo-ionisation. Les concentrations de 137 Cs dans les débris de transport glaciel allaient de moins de 0,2 à 78 Bq·kg -1 (poids sec). Les deux échantillons ayant les concentrations en 137 Cs les plus élevées ont été recueillis à proximité de l'archipel François-Joseph, et leurs trajectoires régressives suggèrent qu'ils proviennent de la mer de Kara. Parmi les plus faibles valeurs de 137 Cs, sept ont été mesurées sur des sédiments arrivés sur la plate-forme ...

Regional variations in provenance and abundance of ice-rafted clasts in Arctic Ocean sediments: implications for the configuration of late Quaternary oceanic and atmospheric circulation in the Arctic

“…Most studies of ice-rafting in the Eurasia basin have also concentrated on the fine-grain fraction (Pfirman et al, 1989(Pfirman et al, , 1990Bischof, 1990;Nürnberg et al, 1994;Nørgaard-Pedersen, 1997;Landa et al, 1998).…”

Modelling Siberian river runoff — implications for contaminant transport in the Arctic Ocean

“…Dethleff et al, 1993;Nurnberg et al, 1994;Pfirman eẗ . al., 1997a,b;Landa et al, 1998 the Laptev and Kara Seas were identified as sources of potentially contaminated sea ice sediments. Entrainment of sediments into newly forming sea ice occurs during fall Ž .…”

Transport of radionuclides by sea-ice and dense-water formed in western Kara Sea flaw leads

“…Cs burden in sea-ice sediments was found at varying sites in the central Arctic Ž Ocean Baskaran et al, 1996;Føyn and Svaeren, . 1997;Landa et al, 1998 . This relationship means that the more polluted fine fraction sea-ice sediments contain, the higher is their radionuclide burden, which underlines again the importance of fine-grained Arctic sea-ice sediments for contaminant transport.…”

“…PII: S 0 9 2 4 -7 9 6 3 9 9 0 0 0 8 8 -3 however, the total recent inventory of 1 PBq 137 Cs and 10 TBq 239,240 Pu may cause significant local and regional ecological problems in the case of a catastrophic -i.e., instantaneous -release. Different recent empirical and modeling studies focus on the pathways of man-made radionuclides with Arctic sea-ice and ocean water masses particu-Ž larly originated from the Kara Sea e.g., Pavlov and Pfirman, 1995;Harms, 1997a;Meese et al, 1997;Baxter et al, 1998;Krosshavn et al, 1998;Landa et . al., 1998;Mitchell et al, 1998 .…”

“…and Landa et al 1998 report enhanced Cs contaminations in central Arctic sea-ice sediments which might have originated from the shallow Siberian shelves and, particularly, from the Kara Sea.…”