• A Recent History of 14C, 137Cs, 210Pb, and 241Am Accumulation at Two Irish Peat Bog Sites: An East versus West Coast Comparison

      Gallagher, Donal; McGee, E. J.; Mitchell, P. I. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Data on radiocarbon (14C), 137Cs, 210Pb, and 241Am levels in an ombrotrophic peat sequence from a montane site on the east coast of Ireland are compared with data from a similar sequence at an Atlantic peatland site on the west coast. The 14C profiles from the west and east coasts show a broadly similar pattern. Levels increase from 100 pMC or less in the deepest horizons examined, to peak values at the west and east coast sites of 117 +/0.6 pMC and 132 +/0.7 pMC, respectively (corresponding to maximal fallout from nuclear weapons testing around 1964), thereafter diminishing to levels of 110-113 pMC near the surface. Significantly, peak levels at the east coast site are considerably higher than corresponding levels at the west coast site, though both are lower than reported peak values for continental regions. The possibility of significant 14C enrichment at the east coast site due to past discharges from nuclear installations in the UK seems unlikely. The 210Pb(ex) inventory at the east coast site (6500 Bq m-2 is significantly higher than at the west coast (5300 Bq m-2) and is consistent with the difference in rainfall at the two sites. Finally, 137Cs and 241Am inventories at the east coast site also exceed those at the west coast site by similar proportions (east:west ratio of approximately 1:1.2).
    • Absolute Dating of Recent Sediments in the Cyclone-Influenced Shelf Area off Bangladesh: Comparison of Gamma Spectrometric (137Cs, 210Pb, 228Ra), Radiocarbon, and 32Si Ages

      Suckow, Axel; Morgenstern, Uwe; Kudrass, Herrmann-Rudolf (Department of Geosciences, The University of Arizona, 2001-01-01)
      A geochronological survey of the Bengal shelf area involved results from more than 20 sediment cores dated using gamma spectrometry and the nuclides 137Cs, 228Ra, 226Ra, and 210Pb. In some cores, which contained older sediments, 32Si and 14C were determined to examine the possibility to extrapolate the obtained chronologies to century and millennial scale. Geochronological work in this region is faced with problems of cyclone-induced sediment reworking, grain-size effects on fallout nuclides, scarcity of carbonates, unknown 14C reservoir effect and sedimentation rates that are too high to obtain sediment cores long enough to establish a chronology. Despite these problems, comparison between the results of the different dating methods provided the most reliable sediment balance to date for the submarine delta of the Ganges-Brahmaputra river system and indicated that on a time scale of several centuries at least 35% of the annual sediment load is deposited.
    • Influence of the Bomb-Produced 14C on the Radiocarbon Concentration in the Youngest Sediments of Lake Gościąż, Central Poland

      Pawlyta, Jacek; Pazdur, Anna; Goslar, Tomasz; Hałas, Stanisław (Department of Geosciences, The University of Arizona, 2001-01-01)
      This work is a study of changes of the radiocarbon concentration in the youngest part of Lake Gościąż sediments in the calendar time scale during the last 150 years. This period includes the time of the nuclear weapons tests performed in the upper atmosphere in the 1950s, and the 1960s, which caused large release of 14C and 137Cs into the environment. On the basis of this study, the isotope dilution factor for 14C and the exchange time of carbon between the atmosphere and Lake Gościąż was estimated. The chronology of the upper part of the sediments was constructed using many interdisciplinary investigations. Among them, measurements of 137Cs in the sediment were used. An unexpected discrepancy between the previously constructed time scale and that suggested by 137Cs is observed in one of the cases.