• A Radiocarbon Chronology for Human-Induced Environmental Change on Mangaia, Southern Cook Islands, Polynesia

      Kirch, P. V.; Flenley, J. R.; Steadman, D. W. (Department of Geosciences, The University of Arizona, 1991-01-01)
      A suite of 23 14C age determinations, from a well-stratified rockshelter and from 3 pollen cores on Mangaia Island is reported. The rockshelter has yielded significant evidence for avifaunal extinctions during the period cal. A.D. 1000-1600. The Lake Tiriara pollen cores span a period from ca. 6500 cal. b.p. to the present, and palynological analysis of the TIR 1 core indicates major anthropogenic disturbance on the island's vegetation after ca. 1600 cal. B.P. These sites, and the radiocarbon ages associated with them, provide the first chronologically secure evidence for human impacts on the island ecosystems of the southern Cook Islands.
    • Cuello: Resolving the Chronology Through Direct Dating of Conserved and Low-Collagen Bone by AMS

      Law, I. A.; Housley, R. A.; Hammond, Norman; Hedges, R. E. M. (Department of Geosciences, The University of Arizona, 1991-01-01)
      It is well known that 14C dating of fossil bone with seriously depleted protein levels, or bone that has been consolidated with preservatives, can produce erroneous results. In the tropics, warm and moist soil conditions lead to constant reworking of organic matter and add to the danger of bone contamination. Because of this, 14C dating of preservative-impregnated bone from such areas has rarely been successful. We report here a set of AMS dates on both unconsolidated animal bone and polyvinyl acetate/polyvinyl alcohol (PVA/PV-OH) impregnated human burials from the Maya site of Cuello, Belize. The steps needed to purify the samples are described, together with details on the use of qualitative infra-red (IR) spectra as a means of assessing sample purity.
    • Late Quaternary Pteropod Preservation in Eastern North Atlantic Sediments in Relation to Changing Climate

      Ganssen, G. M.; Troelstra, Simon R.; van der Borg, Klaas; De Jong, A. M. F. (Department of Geosciences, The University of Arizona, 1991-01-01)
      AMS 14C measurements on pteropod shells from eastern North Atlantic deep-sea cores reveal distinct periods of aragonite preservation during the last 16,000 years. Most preservation spikes coincide with documented periods of climatic change on a scale of 2 x 101 to 2 x 103 years.
    • Lithium Contamination in AMS Measurements of 14C

      Loyd, D. H.; Vogel, J. S.; Trumbore, Susan E. (Department of Geosciences, The University of Arizona, 1991-01-01)
      High count rates of lithium ions in an AMS measurement system for 14C were traced to the lithium content in the quartz tubes used in the graphitization of the samples. The lithium contamination was nearly eliminated by the use of borosilicate glass reaction tubes at a lower reaction temperature. The ion beam current and the measurement precision of the isotope ratio were not affected.
    • Radiocarbon in Seawater and Organisms from the Pacific Coast of Baja California

      Druffel, Ellen R. M.; Williams, Peter M. (Department of Geosciences, The University of Arizona, 1991-01-01)
      Radiocarbon was measured in dissolved inorganic carbon (DIC) and living organisms collected off the west coast of Baja California in October 1980. Samples from three locations were examined. Delta-14C of DIC at the southernmost station was higher than those further north, which reflects reduced upwelling in the southern region. Crabs and anchovies had Delta-14C values significantly lower than surface DIC Delta-14C, indicating the incorporation of ‘older', sediment-derived carbon sources from their diets. Comparisons are made between our DIC Delta-14C measurements and those obtained during other cruises and at a coastal site, from 1959 through 1987. Two distinct time histories of DIC Delta-14C are apparent for the post-bomb period: 1) a lower Delta-14C curve for sites close to the coast influenced by enhanced coastal upwelling; and 2) a higher Delta-14C curve for sites further offshore within the California Current.
    • Shell Hash Dating and Mixing Models for Palimpsest Marine Sediments

      Roy, Peter S. (Department of Geosciences, The University of Arizona, 1991-01-01)
      The dating of palimpsest marine sediments using broken shell fragments (shell hash) is considered to be a necessary but unreliable technique because of the mixed age of the fragments. An analysis of geological mixing models and radiocarbon data on shell hash from sandy sediments on the southeast Australian coast and shelf are used to examine the possibility for simulating the depositional processes, and thus, to better understand the age structure of the deposits.