Radionuclides as Tracers for the Source and Fate of Arctic Sea Ice Sediments.

整个北冰洋的海冰经常以包含细颗粒沉积物为特征。横跨北极的海冰运输为与海冰沉积物相关的颗粒反应性污染物的运输提供了一种机制。主要研究人员将使用天然和人为的放射性核素作为示踪剂，以确定在海冰中运输的颗粒的来源；在海冰沉积物（和相关的放射性核素）通过融化的冰释放后的运输过程中，大气供应在改变海冰污染物负荷方面的重要性。该项目将是一个独特的机会，可以在弗拉姆海峡和巴伦支海的冰融化地区收集海冰、水柱和底部沉积物的样本。首席研究员将与德国研究人员在北极星号上合作，进行为期三年的德国研究。他们将测量海冰沉积物中的两种天然放射性核素（2lOPb和7Be）和人为钚（Pu）同位素。2lOPb（半衰期为22.3年）和7Be（半衰期为53天）都是从大气进入海洋表面的。由于溶解的226Ra的衰变，铅-210也被添加到海水中。进入北极的钚有多种来源，包括原子武器大气试验的沉降物、乏核燃料后处理的投入物、武器生产和核废料的处置。后一种输入集中在喀拉海和拉普捷夫海，那里是海冰形成和颗粒结合的地区。钚的同位素组成是一个敏感的指标，可以将当地的钚源与全球沉降物区分开来。主要研究人员将使用铀同位素比率（24OPu, 241Pu, 242Pu）。239Pu)在海冰沉积物中作为卡拉海和拉普捷夫海沉积物的源示踪剂。还将对沉积物组成和矿物学进行分析，以与Pu数据进行比较。210Pu和7Be的海洋来源特征明确，使这些放射性核素可用于追踪与海冰沉积物运输有关的过程。考虑到冰的过境时间相对于7Be的半衰期较长，7Be与海冰沉积物的联系应该是通过过境期间的大气供应而产生的。对海冰在穿越北极结束时收集的冰和沉积物样本中的7Be进行分析，可以评估大气途径在将这种放射性核素添加到海冰和其他大气输送的污染物（如铅）中的重要性。铅-210可能从大气中被添加到海冰中，或者当沉积物被并入冰中时与它们结合在一起。这种放射性核素提供了一种确定海冰在向海冰消融区输入颗粒和相关颗粒反应性化学物质方面的重要性的方法。先前对东北水冰盆中2lOPb（半衰期= 22.3 y）的研究表明，海冰可能是将这种放射性核素输入冰盆的重要因素。主要研究人员将测量弗拉姆海峡和斯匹茨卑尔根附近海冰沉积物、水柱和底泥样品中的2lOPb，以确定海冰颗粒的输入是否会影响冰消融区2lOPb的质量平衡。这将为评估这一过程是否也会增加这些地区的污染物负担提供初步步骤。

Sea ice throughout the Arctic Ocean is frequently characterized by the inclusion of fine-grained sediments. Transport of sea ice across the Arctic provides a mechanism for the transport of particle-reactive contaminants associated with sea-ice sediment. The Principal Investigators will use natural and anthropogenic radionuclides as tracers for determining the: sources of particles transported in sea ice; importance of atmospheric supply in modifying contaminant burdens of sea ice from during transit fate of sea-ice sediments (and associated radionuclides) after they are released through melted ice.This project will be a unique opportunity to collect samples of sea ice, the water column, and bottom sediments in areas of ice melting in the Fram Strait and Barents Sea. The Principal Investigators will collaborate with German researchers on the Polarstern, on a three-year German research effort. They will measure two natural radionuclides (2lOPb and 7Be) and the anthropogenic plutonium (Pu) isotopes in sea-ice sediments. Both 2lOPb (half-life = 22.3 years) and 7Be (half-life is 53 days) enter the surface ocean from the atmosphere. Lead-210 is also added to seawater from decay of dissolved 226Ra. Plutonium has multiple sources to the Arctic, including fallout from atmospheric testing of atomic weapons, inputs from reprocessing of spent nuclear fuel, weapons production, and disposal of nuclear waste. The latter inputs are focused in the Kara and Laptev Seas which are areas of sea-ice formation and particle incorporation. The isotopic composition of Pu is a sensitive indicator that allows local sources of Pu to be separated from global fallout. The Principal Investigators will use Pu isotope ratios (24OPu, 241Pu, 242Pu. 239Pu) in sea-ice sediments as a source tracer for sediments from the Kara and Laptev Seas. Analyses will also be made of sediment composition and mineralogy to compare with the Pu data.The well-characterized sources of 210Pu and 7Be to the ocean make these radionuclides useful for tracing processes related to the transport of sediments by sea ice. Given the long transit times of ice relative to the half-life of 7Be, the association of 7Be with sea-ice sediments should arise through atmospheric supply during transit. Analyses of 7Be in ice and sediment samples from sea ice collected near the end of its transit across the Arctic will permit assessment of the importance of the atmospheric pathway in adding this radionuclide to sea ice and other atmospherically transported contaminants such as lead.Lead-210 may be added to sea ice from the atmosphere or associated with the sediments when they were incorporated into the ice. This radionuclide provides a means of determining the importance of sea ice in importing particles and associated particle-reactive chemical species to ice ablation areas. Prior studies of 2lOPb (half-life = 22.3 y) in the Northeast Water Polynya suggest that sea ice might be important in importing this radionuclide to the polynia. The Principal Investigators will measure 2lOPb in sea-ice sediments, the water column and bottom sediment samples in the Fram Strait and around Spitzbergen to determine if the import of particles with sea ice can affect the mass balance of 2lOPb in areas of ice ablation. This will provide an initial step toward evaluating whether such a process also can augment contaminant burdens in these areas.