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

放射性核素作为北极海冰沉积物来源和命运的示踪剂。

• 批准号: 9979684
• 负责人: J Kirk Cochran
• 金额: $ 30.5万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9979684&HistoricalAwards=false
• 关键词: Radionuclides; Tracers; Source; Fate; Arctic

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.

整个北冰洋的海冰通常以含有细粒沉积物为特征。海冰穿越北极的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放射性核素作为示踪剂来确定： 海冰中传输的粒子来源；大气供应在改变海冰污染物负担方面的重要性，从海冰沉积物（和相关放射性核素）通过融化的冰释放后的运输过程来看。该项目将是收集海冰、水柱样本的独特机会以及弗拉姆海峡和巴伦支海冰融化区域的底部沉积物。 首席研究员将与德国极星号研究人员合作，进行为期三年的德国研究工作。 他们将测量海冰沉积物中的两种天然放射性核素（21OPb 和 7Be）和人为钚 (Pu) 同位素。 2lOPb（半衰期=22.3年）和7Be（半衰期为53天）均从大气进入海洋表层。 Lead-210 也因溶解的 226Ra 的衰变而添加到海水中。 北极的钚有多种来源，包括原子武器大气层试验的放射性尘埃、乏核燃料后处理的投入、武器生产和核废料处置。后者的输入主要集中在卡拉海和拉普捷夫海，这些区域是海冰形成和颗粒结合的区域。 Pu 的同位素组成是一个敏感指标，可以将当地的 Pu 来源与全球沉降物分开。 主要研究人员将使用海冰沉积物中的 Pu 同位素比率（24OPu、241Pu、242Pu、239Pu）作为卡拉海和拉普捷夫海沉积物的来源示踪剂。还将对沉积物成分和矿物学进行分析，以与 Pu 数据进行比较。海洋中 210Pu 和 7Be 的明确来源使这些放射性核素可用于追踪与海冰沉积物输送相关的过程。 鉴于冰的运输时间相对于 7Be 的半衰期较长，7Be 与海冰沉积物的关联应通过运输过程中的大气供应而产生。 对在北极运输结束时收集的海冰中的冰和沉积物样本中的 7Be 进行分析，将有助于评估大气路径在将这种放射性核素添加到海冰和其他大气传输污染物（如铅）中的重要性。Lead-210可能会从大气中添加到海冰中，或者在融入冰时与沉积物相关联。这种放射性核素提供了一种确定海冰在将颗粒和相关颗粒反应化学物质输入到冰消融区域方面的重要性的方法。 先前对东北水间冰湖中 2lOPb（半衰期 = 22.3 年）的研究表明，海冰对于将这种放射性核素输入冰间湖可能很重要。主要研究人员将测量弗拉姆海峡和斯匹次卑尔根岛周围的海冰沉积物、水柱和底部沉积物样本中的 2lOPb，以确定随海冰进入的颗粒是否会影响冰消融区域中 2lOPb 的质量平衡。这将为评估这样的过程是否也会增加这些地区的污染物负担提供第一步。