• Radiocarbon Analysis of Pinus lagunae Tree Rings: Implications for Tropical Dendrochronology

      Biondi, Franco; Fessenden, Julianna E. (Department of Geosciences, The University of Arizona, 1999-01-01)
      A promising species for tropical dendrochronology is Pinus lagunae, a pine tree found in Baja California Sur (Mexico) around lat 23.5 degrees N. In 1995, we sampled a total of 27 wood cores from 13 Pinus lagunae trees in Sierra La Victoria (23 degrees 36'N, 109 degrees 56'W), just north of Sierra La Laguna, at an elevation of 1500-1600 m. Selected trees were locally dominant, but their ring-width patterns could not be crossdated. To test the hypothesis that visible growth layers in Pinus lagunae are formed annually, we measured radiocarbon amounts in individual rings by means of accelerator mass spectrometry (AMS). Twenty-three 14C measurements were used to trace the location of the 1963-64 "bomb spike" in 3 wood increment cores. By comparing the location of that Delta-14C extreme with the number of visible radial wood increments, it was possible to conclude that 2 cores had a number of locally absent rings, while the 3rd one included a few years with more than one growth layer. Therefore, ring-width patterns of sampled Pinus lagunae were not consistent from one tree to another, most likely because of climatic regime in combination with microsite features. While the possibility of generating Pinus lagunae tree-ring chronologies cannot entirely be ruled out, the development of dendrochronological proxy records of climate from coniferous species in tropical North America should focus on species and sites that experience a more pronounced seasonality.
    • Radiocarbon Laboratories

      Department of Geosciences, The University of Arizona, 1999-01-01
    • Radiocarbon Updates

      Department of Geosciences, The University of Arizona, 1999-01-01
    • Radiocarbon, Volume 41, Number 3 (1999)

      Department of Geosciences, The University of Arizona, 1999-01-01
    • Reporting 14C Activities and Concentrations

      Mook, Willem G.; van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 1999-01-01)
      Three modes of reporting 14C activities are in use, in part analogous to the internationally accepted (IAEA) conventions for stable isotopes: (1) absolute activity, the specific activity of 14C or the activity per gram of carbon; (2) activity ratio, the ratio between the absolute activities of a sample and the standard; and (3) relative activity, the difference between the absolute activities of a sample and standard material, relative to the absolute standard activity. The basic definitions originate from decisions made by the radiocarbon community at its past conferences. Stuiver and Polach (1977) reviewed and sought to specify the definitions and conventions. Several colleagues, however, have experienced inadequacies and pitfalls in the definitions and use of symbols. Furthermore, the latter have to be slightly amended because of the use of modern measuring techniques. This paper is intended to provide a consistent set of reporting symbols and definitions, illustrated by some practical examples.
    • Subject Index Volume 41, 1999

      Department of Geosciences, The University of Arizona, 1999-01-01
    • The Spatial and Temporal Patterns of Stick-Nest Rat Middens in Australia

      Pearson, Stuart; Lawson, Ewan; Head, Lesley; McCarthy, Lynne; Dodson, John (Department of Geosciences, The University of Arizona, 1999-01-01)
      The spatial and temporal distribution of 145 radiocarbon dates on 66 Australian stick-nest rat middens (Muridae: Leporillus spp.) range from modern to 10,900 +/90 BP. As in American packrat middens, age frequency follows a logarithmic decay, both continentally and at major sites. This is probably a result of natural decay processes. Unlike American middens of similar age, relatively few range changes in plant distribution have been detected in Australia. The distribution of 14C ages and the associated midden materials provide important paleoenvironmental information from the arid interior of Australia. The middens record subtle changes in vegetation and dramatic changes in the fauna unlike those interpreted from sites on the coastal rim or the southeastern periphery of the arid zone.