• The IAEA 14C Intercomparison Exercise 1990

      Rozanski, Kazimierz; Stichler, Willibald; Gonfcantini, Roberto; Scott, E. M.; Beukens, R. P.; Kromer, Bernd; van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 1992-01-01)
      As a follow-up to the meeting of experts convened at the International Atomic Energy Agency (IAEA) in February 1989, and the International 14C Workshop held in Glasgow in September 1989, the 14C Quality Assurance Program was formulated. In a joint effort of several radiocarbon teams and IAEA staff, we have prepared a set of five new intercomparison materials. These are natural materials frequently used by radiocarbon laboratories. The materials were distributed to 137 laboratories in May 1990. In February 1991, a meeting of experts was convened in Vienna to evaluate the results, to determine the radiocarbon activity of the five samples expressed in % Modern (pMC) terms and to define the 13C/12C ratio, and to make recommendations on further use of these materials. We present here the results of the exercise and the agreed consensus values for each of the five materials and discuss the different analyses that were undertaken.
    • The Impact of Accelerator Dating at the Early Village of Abu Hureyra on the Euphrates

      Moore, A. M. T. (Department of Geosciences, The University of Arizona, 1992-01-01)
      The early village of Abu Hureyra is significant because of its great size (ca. 11.5 ha) and long sequence of occupation (ca. 11,500-7000 BP) that spans the transition from late Pleistocene hunting and gathering to early Holocene farming, and the cultural change from Epipaleolithic to Neolithic. The 40 accelerator dates obtained for Abu Hureyra provide new information on the development of agriculture in Southwest Asia. The dates have demonstrated that the site was inhabited for much longer than the few conventional radiocarbon dates for the site had suggested. The gap between the Epipaleolithic and Neolithic villages seems to have been brief. A change in climate and vegetation, dated at ca. 10,600 BP, during the span of occupation of the Epipaleolithic village, precipitated an adjustment in the foraging way of life of its inhabitants just before the inception of agriculture. Dating of individual bones and seeds has shown that the wild progenitors of sheep and several cereals were present near Abu Hureyra in the late Pleistocene and early Holocene, well outside their present areas of distribution. This has implications for where those species may have been domesticated. A rapid switch from exploitation of the gazelle to herding of sheep and goats during the Neolithic occupation occurred ca. 8300 BP.
    • The New Groningen 14C Data Base

      van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 1992-01-01)
      The Groningen Radiocarbon Data base has been operating on an Apple lIe PC until recently. Both software and hardware of this data base made exchange with other systems very difficult. Therefore, the data base has been transferred to an IBM AT compatible computer. A new program has been written in Turbo-Pascal, using the Turbo-Pascal Database Toolbox. The program features versatile search routines. The output can be directed to various date-list formats, such as the International Radiocarbon Data Base (IRDB). The program is written in such a way that new date lists can be added with minor adjustments to the source code.
    • The New National Ocean Sciences Accelerator Mass Spectrometer Facility at Woods Hole Oceanographic Institution: Progress and First Results

      Von Reden, K. F.; Jones, G. A.; Schneider, R. 1.; McNichol, A.; Cohen, G. J.; Purser, K. H. (Department of Geosciences, The University of Arizona, 1992-01-01)
      Start-up performance and first results of the new Woods Hole Accelerator Mass Spectrometer are discussed. Special attention is given to the hemispherical ionizer sputter source and the triple-isotope injector design.
    • The Statistics of Low-Level Counting Using the New Generation of Packard Liquid Scintillation Counters

      Cook, G. T.; Scott, E. M.; Wright, E. M.; Anderson, Robert (Department of Geosciences, The University of Arizona, 1992-01-01)
      We consider the suitability of commonly used Poisson counting statistics applied to background count rates measured in the new generation of low-background Packard liquid scintillation spectrometers. We also investigate the stability of these systems over long time intervals. Undetected instability will result in an underestimation of the precision of any result (i.e., the calculated error will be too small), and, in the presence of a systematic source, could lead to inaccurate results. The work described here forms only a small part of a project to investigate the statistical criteria that should be applied to the performance of such counters. The procedures to be discussed here include the Poisson index of dispersion, x and s control charts and the MSSD test for detection of drift. These are illustrated on background count rates derived from the Packard 2260XL and 2000CA/LL.
    • The Use of Natural 14C and 13C in Soils for Studies on Global Climate Change

      Becker-Heidmann, Peter; Scharpenseel, Hans-Wilhelm (Department of Geosciences, The University of Arizona, 1992-01-01)
      Some examples are given to show that the depth distribution curves of natural 14C and 13C of thin-layer sampled soil profiles can be used for inferring changes in soil organic matter and climate changes. By using a simple exchange model, we can determine whether decomposition products are fixed by clay or transported downward toward the groundwater table. We can also estimate the amount of the Greenhouse gases, CO2 and CH4, produced by the decomposition of the organic matter in terrestrial and paddy soils and emitted from the soil. A change from C3 to C4 plants, which might occur during a predicted temperature rise in some areas, thereby influencing the carbon balance, can be clearly detected by the delta-13C depth profiles. A change in organic matter input can also be calculated under certain circumstances.
    • Twenty-Five Years of Radiocarbon Dating Soils: Paradigm of Erring and Learning

      Scharpenseel, H.-W.; Becker-Heidmann, Peter (Department of Geosciences, The University of Arizona, 1992-01-01)
      Soil organic matter sequesters close to three times the carbon existing totally in the living biomass and nearly the same for the total carbon in the atmosphere. Models, such as Jenkinson's or Parton's Century model, help to define soil organic matter fractions of different functions, based on residence time/14C age. Rejuvenation of soil carbon was felt to be the principal impediment to absolute soil dating, in addition to the ambiguity of the initiation point of soil formation and soil age. Recent studies, for example, of Becker-Heidmann (1989), indicate that a soil 14C age of >1000 yr cannot have >0.1% rejuvenation in the total soil organic matter compartments/fractions to be possible and sustainable. Always problematic in earlier observations were age vs. depth increases, in 14C profile curves showing an inflection of reduced age in the deepest samples, i.e., from the rim of the organic matter containing epipedon. We attribute this phenomenon, in mollic horizons, to earthworm casts in the terminal part of the escape tube. Becker-Heidmann (1989) has shown, in thin layer soil profile dating, a highly significant correlation between the highest 14C ages and the highest clay content. Thus, optimization of soil dating is, to a lesser degree, related to the applied extracting solvent system than to soil texture fractions. Such observations allow us to mitigate error ranges inherent in dating dynamic soil systems.