Radioactivity levels in a firn core from the Yukon Territory,Canada |
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| Affiliation: | 1. Department of Forestry, Michigan State University, 480 Wilson Rd., Rm. 126, East Lansing, MI 48824, United States;2. School of Forest Resources, University of Maine, 241 Nutting Hall, Orono, ME 04469, United States;3. Department of Environmental Conservation, University of Massachusetts, 160 Holdsworth Way, Amherst, MA 01003, United States;4. School of Economics, University of Maine, 207 Winslow Hall, Orono, ME 04469, United States;5. School of Forest Resources, University of Maine, 229 Nutting Hall, Orono, ME 04469, United States;1. Institute for the Dynamics of Environmental Processes, IDPA/CNR - Via Torino 155, (I) 30172 Venezia-Mestre (VE), Italy;2. University Ca'' Foscari of Venice, Department of Environmental Sciences, Informatics and Statistics, Via Torino 155, (I) 30172 Venezia-Mestre (VE), Italy;3. Laboratoire de Glaciologie et Géophysique de l''Environnement (UMR UJF/CNRS 5183), 54, rue Molière, Domaine Universitaire, B.P. 96, 38402 Saint Martin d'' Hères, France;1. USDA Forest Service, 1033 University Place, Evanston, IL 60201, USA;2. College of Natural Resources, University of Wisconsin – Stevens Point, 800 Reserve Street, Stevens Point, WI 54481, USA;3. Department of Forestry, Michigan State University, Natural Resources Building, 480 Wilson Road, East Lansing, MI 48824–6402, USA;4. North Dakota Parks and Recreation Department, 1600 Sentry Avenue, Suite 3, Bismarck, ND 58503, USA |
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| Abstract: | Gross β-activity and tritium concentration measurements made on a 26.8m length of consolidated snow (firn) core retrieved from an altitude of 5340 m on Mt. Logan (Yukon Territory, Canada) have revealed a detailed chronology of natural and anthropogenic radioactivity levels extending from about 1943 to 1980. Oxygen isotope measurements were used to assist in the dating of the core and a reliable time scale spanning 1950–1980 has been established with an accuracy of at least ± 0.5 y, and in some cases ± 0.25y.An immediate result is the establishment of mean annual accumulation rates, which are, for the years 1963–1980: 0.36m y−1 and for 1951–1980: 0.39m y− water equivalent. Another result is the estimation of the ‘stratospheric residence time’ for the fission fallout products (mainly 90Sr and 137Cs). A value of the stratospheric residence time of about 1 y is derived from data spanning 1963–1967.Reference to the history of atmospheric thermonuclear device testing shows that individual or specific groups of tests by different countries can be identified.Comparison of the gross β-activity data with a similar set from Station Centrale (Greenland) shows that although the same trends exist in the two data sets, the amplitude of most corresponding major peaks in the Greenland data is significantly lower. Since the accumulation rates at the two sites are almost identical and since the deposition of radioactive aerosols in any case is expected to be dominated by dry fall-out, the differences are assumed to be related to the trajectory path and to the diffusion rates of the radionuclide clouds. |
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