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

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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.