• In-Situ Radiocarbon Production by Neutrons and Muons in an Antarctic Blue Ice Field at Scharffenbergbotnen: A Status Report

      van der Borg, K.; van der Kemp, W. J. M.; Alderliesten, C.; de Jong, A. F. M.; Lamers, R. A. N.; Oerlemans, J.; Thomassen, M.; van de Wal, R. S. W. (Department of Geosciences, The University of Arizona, 2001-01-01)
      In the radiocarbon accelerator mass spectrometry (14C AMS) analysis of gases obtained in a dry extraction from a 52-m Antarctic ice core, we observed 14CO2 and 14CO concentrations decreasing with depth. The concentrations are explained in terms of in-situ production by neutrons and captured muons in ablating ice. The ratio of the 14CO2 concentration to that of 14CO has been found to be constant at 1.9 +/0.3. The ablation rates obtained of 42 +/18 cm.yr-1 and 40 +/13 cm.yr-1 for the neutron and muon components, respectively, are about three times higher than observed from stake readings. The discrepancy may point to an incomplete extraction of the dry extraction method. Using the constant ratio in 14CO2 and 14CO concentrations we correct for the in-situ component in the trapped 14CO2 and deduce an age of 10,300 +/900 BP for the ice core.
    • The Late Quaternary Sedimentary Record of Reykjanes Ridge, North Atlantic

      Prins, M. A.; Troelstra, S. R.; Kruk, R. W.; van der Borg, K.; de Jong, A. F. M.; Weltje, G. J. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Variability in surface and deep ocean circulation in the North Atlantic is inferred from grain-size characteristics and the composition of terrigenous sediments from a deep-sea core taken on Reykjanes Ridge, south of Iceland. End-member modeling of grain size data shows that deep-ocean circulation in this area decreased significantly during periods of maximum iceberg discharge. The episodes of reduced circulation correlate with the cold and abrupt warming phases of the Dansgaard-Oeschger cycles as recognized in the Greenland ice cores.