• Performance of Models for Radiocarbon Dating of Groundwater: An Appraisal Using Selected Irish Aquifers

      Gallagher, D.; McGee, E. J.; Kalin, R. M.; Mitchell, P. I. (Department of Geosciences, The University of Arizona, 2000-01-01)
      Appropriate management strategies are essential for the protection and maintenance of groundwater resources. It is therefore important that aquifers are understood in terms of hydraulics, recharge, and yield potential, and that the vulnerability of aquifers to surface pollution is evaluated. A range of aquifer types were examined in this study, and water samples were analyzed for the radiocarbon content of the total dissolved inorganic carbon (TDIC), stable isotopes, and a suite of chemical and physical parameters. The data were input to a selection of models for the estimation of the initial activity of the TDIC, and groundwater ages were calculated. Eight commonly used models were comparatively assessed in the study. The Tamers, Mook, and IAEA models gave anomalous ages, probably because of their inability to correct for solid phase isotopic exchange in aquifers. The Pearson, F&G, Evans, Eichinger, and Mass Balance models produced results in broad agreement. The study shows that contrary to popular belief, there are sources of ancient groundwater in Ireland. Of the 19 sampling stations, two boreholes yielded waters with age estimates of greater than 10,000 BP. Water samples from a further six sites returned ages of between around 800 and 4000 BP. In contrast to borehole samples, spring wells yielded water of consistently young ages, demonstrating rapid recharge and flow mechanisms. Samples from several spring wells produced negative ages, indicating the presence of anthropogenic 14C. The findings demonstrate the potential for contamination of springs by surface runoff, while sources of greater age generally offer a greater degree of protection from surface pollution.
    • Accelerator Mass Spectrometry Analysis of Non-Soluble Carbon in Aerosol Particles from High Alpine Snow (Mt. Sonnblich, Austria)

      Weissenbök, Roland H.; Currie, Lloyd A.; Gröllert, Christina; Kutschera, Walter; Marolf, Julie; Priller, Alfred; Puxbaum, Hans; Rom, Werner; Steier, Peter (Department of Geosciences, The University of Arizona, 2000-01-01)
      With an elaborate accelerator mass spectrometry (AMS) technique radiocarbon measurements have been performed with aerosol carbon filtered from high alpine snow samples gathered consecutively at the high-altitude research station Sonnblick (3106 m, Eastern Alps, Austria) during a snow storm in April 1997. The concentration of the water-insoluble carbonaceous material in the molten snow was on the average 310 micrograms C/L and the total sample amounts for analysis were in the range of 35 micrograms to 60 micrograms C. Using a special background correction procedure tested on similar amounts of an urban particulate standard sample the accuracy of the corrected and normalized 14C/12C isotopic ratios of the snow aerosol samples was in the order of 4% to 14% of the measured ratios. The water-insoluble carbonaceous material of five samples from Mt. Sonnblick exhibited a weighted mean of 74 pMC (percent Modern Carbon) with a range of 64 pMC to 88 pMC. Thus, it appears that about 64% of non-soluble carbon in high alpine snow from Sonnblick was of biogenic origin. The temporal variations of the 14C/12C isotopic ratios of the snow aerosol samples were statistically significant, suggesting alterations in the contribution of specific aerosol sources.
    • Radiocarbon, Volume 42, Number 2 (2000)

      Department of Geosciences, The University of Arizona, 2000-01-01
    • AMS Dating Mammoth Bones: Comparison with Conventional Dating

      Vasil'chuk, Y. K.; Vasil'chuk, A. C.; Long, Austin; Jull, A. J. T.; Donahue, D. J. (Department of Geosciences, The University of Arizona, 2000-01-01)
      Fossilized Siberian mammoth remains are important indicators of environmental change in the Late Pleistocene. The NSF-Arizona AMS Laboratory radiocarbon results on amino acid separations compare well with mammoth bone collagen from the same specimens treated by HCI and dated by beta counting (the Russian Academy Geological Institute Radiocarbon Laboratory). Neither laboratory was aware of the other's dates for these comparisons. The results coincide very closely (a difference of 50-800 yr), and demonstrate that AMS dating provides a very good perspective for applications of past mammoth population studies.
    • Comment on 'The Use of Bayesian Statistics for 14C Dates of Chronologically Ordered Samples: A Critical Analysis'

      Bronk Ramsey, Christopher (Department of Geosciences, The University of Arizona, 2000-01-01)
    • Mammoths, Measured Time, and Mistaken Identities

      Haynes, Gary (Department of Geosciences, The University of Arizona, 2000-01-01)
      Mammoth and mastodont sites containing broken or cut bones are not rare in the New World, but their meanings are ambiguous. Studies of recent African elephant bone sites indicate that certain processes in nature create bone modifications that are identical to the end-effects of human actions such as butchering. In designing a rational and efficient approach to the radiometric dating of fossil proboscidean sites, caution and skepticism should enter into interpretations of modified materials.
    • The Radiocarbon Content of Individual Lignin-Derived Phenols: Technique and Initial Results

      McNichol, A. P.; Ertel, J. R.; Eglinton, T. I. (Department of Geosciences, The University of Arizona, 2000-01-01)
      We present a method for the isolation of phenolic compounds derived from lignin for radiocarbon analysis.These phenols are generated by chemical oxidation of polymeric materials and derivatized for separation and recovery by pre-parative capillary gas chromatography (PCGC). This technique yields tens of micrograms of pure, stable compounds that canbe converted to graphite and analyzed by accelerator mass spectrometry (AMS). Analysis of model flavor compounds anddated woods indicates that, in most cases, the radiocarbon (14C) contents of the individual compounds, corrected for the con-tribution of the derivative, agree with that of the bulk material to within 20‰.
    • The Use of Bayesian Statistics for 14C Dates of Chronologically Ordered Samples: A Critical Analysis

      Steier, Peter; Rom, Werner (Department of Geosciences, The University of Arizona, 2000-01-01)
      Bayesian mathematics provides a tool for combining radiocarbon dating results on findings from an archaeological context with independent archaeological information such as the chronological order, which may be inferred from stratigraphy. The goal is to arrive at both a more precise and a more accurate date. However, by means of simulated measurements we will show that specific assumptions about prior probabilities—implemented in calibration programs and not evident to the user—may create artifacts. This may result in dates with higher precision but lower accuracy, and which are no longer in agreement with the true ages of the findings.
    • Radiocarbon Updates

      Department of Geosciences, The University of Arizona, 2000-01-01
    • Erratum

      Jull, Tim (Department of Geosciences, The University of Arizona, 2000-01-01)
    • Southwest Subtropical Pacific Surface Water Radiocarbon in a High-Resolution Coral Record

      Guilderson, Thomas P.; Schrag, Daniel P.; Goddard, Ethan; Kashgarian, Michaele; Wellington, Gerard M.; Linsley, Braddock K. (Department of Geosciences, The University of Arizona, 2000-01-01)
      We have generated a high-resolution coral D14C record from the southwest subtropical Pacific spanning the last 50 yr. Prebomb (1950-1956) Delta-14C values average -52‰. Values begin to increase in 1957, reaching a maximum in the early 1970s, about 10 yr after the atmospheric peak. There is a consistent 10-15‰ seasonal cycle whose relationship with vertical mixing evolves as a consequence of the penetration of the bomb transient into subsurface waters. Comparison of this record with that simulated in an ocean general circulation model highlights the difficulty in modeling vertical exchange processes.
    • From the Editor

      Jull, Tim (Department of Geosciences, The University of Arizona, 2000-01-01)
    • Radiocarbon Reservoir Ages in the Mediterranean Sea and Black Sea

      Siani, Giuseppe; Paterne, Martine; Arnold, Maurice; Bard, Edouard; Métivier, Bernard; Tisnérat, Nadine; Bassinot, Franck (Department of Geosciences, The University of Arizona, 2000-01-01)
      We measured apparent marine radiocarbon ages for the Mediterranean Sea, Black Sea, and Red Sea by accelerator mass spectrometry radiocarbon analyses of 26 modern, pre-bomb mollusk shells collected living between AD 1837 and 1950. The marine reservoir (R(t)) ages were estimated at some 390 +/85 yr BP, 415 +/90 yr BP and 440 +/40 yr BP, respectively. R(t) ages in the Mediterranean Sea and Black Sea are comparable to those for the North Atlantic Ocean (<65 degrees N), inaccordance with the modern oceanic circulation pattern. The Delta-R values of about 35 +/70 yr and 75 +/60 yr in the Mediterranean area show that the global box-diffusion carbon model, used to calculate R(t) ages, reproduces the measured marine 14C R(t) ages in these oceanic areas. Nevertheless, high values of standard deviations, larger than measurement uncertainties are obtained and express decadal R(t) changes. Such large standard deviations are indeed related to a decrease of the apparent marine ages of some 220 yr from 1900 AD to 1930 AD in both the Mediterranean Sea and the western North Atlantic Ocean.
    • Redating Iztapan and Valsequillo, Mexico

      Pichardo, Mario (Department of Geosciences, The University of Arizona, 2000-01-01)
      Recent radiocarbon dating of tephra sequences and biostratigraphic analysis in the Valley of Mexico and the Valley of Puebla, respectively, reveal that the FAD (first appearance date) for lanceolate Lerma/El Jobo points at Iztapan and Hueyatlaco archeological sites at about 14-16,000 BP predates the Clovis culture FAD. A lack of interdisciplinary communication is responsible for the neglect of these sites for three decades.
    • Bayesian Methods: What Can We Gain and at What Cost?

      Scott, Marian (Department of Geosciences, The University of Arizona, 2000-01-01)
    • Improved Results Using Higher Ratios of Scintillator Solution to Benzene in Liquid Scintillation Spectrometry

      Koba, Motoharu (Department of Geosciences, The University of Arizona, 2000-01-01)
      Practical effects of the volumetric or weight ratio of scintillator solution to sample benzene in liquid scintillation spectrometry were examined here for radiocarbon dating. It is concluded, using a LKB-Wallac Quantulus(TM) 1220 and Teflon(TM)-copper 3 mL vials with scintillator of toluene-based PPO and POPOP, that solutions containing the same concentrations of the same ratio, 1.3 or more, of scintillator solution to sample benzene show the same cpm/g and the same channel value of external standard spectrum, irrespective of different gross volumes of solutions. The addition of scintillator solution reduces background in 0.5 mL or so of benzene, and results in an appreciably enlarged figure of merit.
    • Effects of 14C Sample Selection in Archaeology: An Example from Hawai'i

      Dye, Tom (Department of Geosciences, The University of Arizona, 2000-01-01)
      A comparison of radiocarbon histograms of samples controlled and uncontrolled for sample provenance and composition factors indicates that differences are sufficiently large to influence the discrimination of alternative hypotheses on the age of the important, early Bellows Dune site in Hawai'i.
    • Radiocarbon Dates from a Holocene Deposits in Southwestern Australia

      Dodson, J. R.; Zhou, Weijian (Department of Geosciences, The University of Arizona, 2000-01-01)
      A radiocarbon chronology has been developed using shell, bulk peat, and paired charcoal and pollen preparations from a peat and clay sequence in southwestern Australia. The results indicate the sequence is of Holocene age, and the mid-Holocene was a period of rapid sediment deposition. The earliest record is based on Bothriembyron sp. Snail shell and there is a strong indication that the deposit had a stratigraphic hiatus between 9600 and 4700 BP. Modern shell of the snail has no ancient reservoir effect. The bulk peat ages were a little younger than associated AMS determinations on hand-picked charcoal and residues from pollen preparations. As a group, paired charcoal and pollen based dates were indistinguishable in age. This implies that the sedimentary charcoal shows no significant storage and transport time in the catchment before deposition. This is important when interpreting pollen records and sedimentary charcoal to reconstruct fire and vegetation dynamics and inter-relationships.