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

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 137Cs by gamma spectrometry and for 239Pu and 240Pu by thermal ionization mass spectrometry. 137Cs concentrations in the IRD ranged from less than 0.2 to 78 Bq/kg (dry weight basis). The two samples with the highest 137Cs concentrations were collected in the vicinity of Franz Josef Land, and their backward trajectories suggest origins in the Kara Sea. Among the lowest 137Cs 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 239Pu + 240Pu ranged from about 0.02 to 1.8 Bq/kg. 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 240Pu/239Pu 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.  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 137Cs par spectrométrie gamma ainsi que du 239Pu et du 240Pu par spectrométrie de masse réalisée par thermo-ionisation. Les concentrations de 137Cs dans les débris de transport glaciel allaient de moins de 0,2 à 78 Bq/kg (poids sec). Les deux échantillons ayant les concentrations en 137Cs 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 137Cs, sept ont été mesurées sur des sédiments arrivés sur la plate-forme continentale nord-américaine en 1989 et 1995 et prélevés sur celle-ci moins de six mois plus tard. Les concentrations en 239Pu et 240Pu allaient d'environ 0,02 à 1,8 Bq/kg. Les deux valeurs les plus élevées venaient d'échantillons recueillis au centre du bassin Canada et près du Spitzberg; le calcul des trajectoires régressives suggère que le 239Pu est resté au moins 14 ans en circulation dans le bassin Canada et que le 240Pu tire son origine des environs de Severnaïa Zemlia (à la frontière de la mer de Kara et de la mer des Laptev). Tandis que la plupart des échantillons de débris de transport glaciel révélaient des rapports 240Pu/239Pu proches de la valeur moyenne (0,185) des retombées radioactives mondiales, cinq des échantillons affichaient des rapports inférieurs, allant de 0,119 à 0,166. Cette fourchette est caractéristique de mélanges de Pu provenant de retombées radioactives et du retraitement du Pu pouvant être utilisé à des fins militaires. Les trajectoires régressives de ces cinq échantillons suggèrent qu'ils proviennent de la mer de Kara ou des environs de Severnaïa Zemlia

Field and Satellite Observations of the Formation and Distribution of Arctic Atmospheric Bromine Above a Rejuvenated Sea Ice Cover

Recent drastic reduction of the older perennial sea ice in the Arctic Ocean has resulted in a vast expansion of younger and saltier seasonal sea ice. This increase in the salinity of the overall ice cover could impact tropospheric chemical processes. Springtime perennial ice extent in 2008 and 2009 broke the half-century record minimum in 2007 by about one million km2. In both years seasonal ice was dominant across the Beaufort Sea extending to the Amundsen Gulf, where significant field and satellite observations of sea ice, temperature, and atmospheric chemicals have been made. Measurements at the site of the Canadian Coast Guard Ship Amundsen ice breaker in the Amundsen Gulf showed events of increased bromine monoxide (BrO), coupled with decreases of ozone (O3) and gaseous elemental mercury (GEM), during cold periods in March 2008. The timing of the main event of BrO, O3, and GEM changes was found to be consistent with BrO observed by satellites over an extensive area around the site. Furthermore, satellite sensors detected a doubling of atmospheric BrO in a vortex associated with a spiral rising air pattern. In spring 2009, excessive and widespread bromine explosions occurred in the same region while the regional air temperature was low and the extent of perennial ice was significantly reduced compared to the case in 2008. Using satellite observations together with a Rising-Air-Parcel model, we discover a topographic control on BrO distribution such that the Alaskan North Slope and the Canadian Shield region were exposed to elevated BrO, whereas the surrounding mountains isolated the Alaskan interior from bromine intrusion

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a Special Observing Period (SOP) that ran from November 16, 2018 to February 15, 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

International audienceThe Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a special observing period (SOP) that ran from 16 November 2018 to 15 February 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2,200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes yield the greatest forecast improvement for deep cyclones near the Antarctic coast. The SOP data have been applied to provide insights on an atmospheric river event during the YOPP-SH SOP that presented a challenging forecast and that impacted southern South America and the Antarctic Peninsula. YOPP-SH data have also been applied in determinations that seasonal predictions by coupled atmosphere–ocean–sea ice models struggle to capture the spatial and temporal characteristics of the Antarctic sea ice minimum. Education, outreach, and communication activities have supported the YOPP-SH SOP efforts. Based on the success of this Antarctic summer YOPP-SH SOP, a winter YOPP-SH SOP is being organized to support explorations of Antarctic atmospheric predictability in the austral cold season when the southern sea ice cover is rapidly expanding