• An Extraction System to Measure Carbon-14 Terrestrial Ages of Meteorites with a Tandetron AMS at Nagoya University

      Minami, Masayo; Nakamura, Toshio (Department of Geosciences, The University of Arizona, 2001-01-01)
      We have constructed a system to extract carbon from meteorites using a vacuum-tight RF melting method in order to study radiocarbon activities in meteorites. The extraction system was examined using iron standards of known carbon content. The carbon extraction efficiencies and 14C ages of the iron standards by this method were compared with the results obtained previously by our older melting system and a wet oxidation method. Higher collection efficiencies of about 90% for the iron samples of relatively high carbon content were achieved by the new system. The efficiency of extracting a small amount of carbon is also near 90% after improving the extraction procedure. The 14C ages of the iron standards were compared to the ages by the wet method. The results indicate that contamination by modern carbon is negligible in the system. Furthermore, terrestrial 14C ages of two Antarctic meteorites, Y-75102 and ALH-77294, from the Yamato and Allan Hills ice fields, respectively, were determined. The age of Y-75102 is estimated 4.0 +/1.0 ka, and the age of ALH-77294 is 19.5 +/1.2 ka. The 14C ages on the meteorites roughly agree with the literature value. However, further study is needed in improvement on reducing a background value and of complete fusion of a meteorite in the extraction system.
    • Development of the Radiocarbon Calibration Program

      Bronk Ramsey, Christopher (Department of Geosciences, The University of Arizona, 2001-01-01)
      This paper highlights some of the main developments to the radiocarbon calibration program, OxCal. In addition to many cosmetic changes, the latest version of OxCal uses some different algorithms for the treatment of multiple phases. The theoretical framework behind these is discussed and some model calculations demonstrated. Significant changes have also been made to the sampling algorithms used which improve the convergence of the Bayesian analysis. The convergence itself is also reported in a more comprehensive way so that problems can be traced to specific parts of the model. The use of convergence data, and other techniques for testing the implications of particular models, are described.
    • Marine Radiocarbon Reservoir Effect in the Western North Pacific Observed in Archaeological Fauna

      Yoneda, Minoru; Hirota, Masashi; Uchida, Masao; Uzawa, Kazuhiro; Tanaka, Atsushi; Shibata, Yasuyui; Morita, Masatoshi (Department of Geosciences, The University of Arizona, 2001-01-01)
      Faunal remains originating from terrestrial and marine mammals, and belonging to the same archaeological deposits were compared to evaluate the marine radiocarbon reservoir ages around the Hokkaido island, Japan. From five shell middens of different ages from the Jomon period (4900 BP) to the Ainu cultural period (800 BP), 107 animal bone samples were selected for radiocarbon measurements. The apparent age differences between Japanese deer and northern fur seal showed the clear effect of deep-water upwelling in this region. Our data showed relatively stable age differences from 4500 BP to 800 BP, with an estimated Delta-R values around 380 14C yr. Results are consistent with previous estimation based on simulation models and oceanographic properties.
    • Preparation of Graphite Targets in the Gliwice Radiocarbon Laboratory for AMS 14C Dating

      Czernik, Justyna; Goslar, Tomasz (Department of Geosciences, The University of Arizona, 2001-01-01)
      A line for preparation of graphite targets for accelerator mass spectrometry (AMS) radiocarbon dating has been built in the Gliwice 14C Laboratory. The AMS 14C measurements of our targets are performed in the Leibniz-Labor fur Altersbestimmung, Kiel, Germany. The quality of our line has been tested in two series of AMS 14C measurements of background and Ox-II standard samples and by measurements of the amount of CO2 released during combustion of sample-free quartz tubes. Most background contamination in the first series was introduced during combustion, which has been greatly reduced by baking quartz tubes vacuum-sealed with CuO and Ag. The residual contamination (ca. 1.5 micrograms C) seems to come mostly from the quartz tubes themselves. At present, most of the contamination of the background is introduced during graphitization. The reproducibility of background preparations is satisfactory, especially for samples larger than 1.5 mg, when it is better than +/0.09 pMC. Despite still significant contamination with low-14C carbon during the graphitization process (corresponding to 1.2 +/0.2% of 14C-free carbon), the good reproducibility of the results allows us to use our line in routine 14C dating.
    • Radiocarbon Dating of Single Compounds Isolated from Pottery Cooking Vessel Residues

      Stott, A. W.; Berstan, R.; Evershed, P.; Hedges, Robert E. M.; Bronk Ramsey, Christopher; Humm, M. J. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We have developed and demonstrated a practical methodology for dating specific compounds (and octadecanoic or stearic acid—C18:0—in particular) from the lipid material surviving in archaeological cooking pots. Such compounds may be extracted from about 10 g of cooking potsherd, and, after derivatization, can be purified by gas chromatography. To obtain sufficient material for precise dating repetitive, accumulating, GC separation is necessary. Throughout the 6000-year period studied, and over a variety of site environments within England, dates on C18:0 show no apparent systematic error, but do have a greater variability than can be explained by the errors due to the separation chemistry and measurement process alone. This variability is as yet unexplained. Dates on C16:0 show greater variability and a systematic error of approximately 100-150 years too young, and it is possible that this is due to contamination from the burial environment. Further work should clarify this.
    • Radiocarbon Dating of Wood Using Different Pretreatment Procedures: Application to the Chronology of Rotoehu Ash, New Zealand

      Santos, Guaciara M.; Bird, M. I.; Fifield, L. Keith; Alloway, B. V.; Chappell, J.; Hausladen, P. A.; Arneth, A. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We compare radiocarbon accelerator mass spectrometry (AMS) ages of wood samples subjected to a conventional acid-base-acid pretreatment with stepped combustion (ABA-SC) with results from the same samples subjected to an acid-base-wet oxidation pretreatment with stepped combustion (ABOX-SC) and cellulose extraction with stepped combustion (CE-SC). The ABOX-SC procedure has been shown previously to lead to lower backgrounds for old charcoal samples. Analyses of relatively uncontaminated " 14C-dead" samples of wood suggest that backgrounds of 0.11 +/0.04 pMC are obtainable for both the ABOX-SC and ABA-SC procedures. Where wood is significantly contaminated the ABOX-SC technique provides significantly better decontamination than either the ABA-SC technique or cellulose extraction alone, although CE-SC can produce comparably low backgrounds to the ABOX-SC procedure. We also report the application of the ABOX-SC, ABA-SC and CE-SC procedures to wood samples associated with the chronologically controversial Rotoehu Ash eruption, New Zealand. New 14C-AMS dates from wood sampled from below the Rotoehu Ash span an age range of 43-50 ka BP consistent with recently presented OSL dates of 42-44 ka obtained for palaeosols beneath the ash.
    • Sample Preparation of Dissolved Organic Carbon in Groundwater for AMS 14C Analysis

      Burr, George S.; Thomas, J. M.; Reines, D.; Jeffrey, D.; Courtney, C.; Jull, A. J. Timothy; Lange, Todd (Department of Geosciences, The University of Arizona, 2001-01-01)
      This study describes a sample preparation technique used to isolate dissolved organic carbon (DOC) in groundwater for radiocarbon analysis using accelerator mass spectrometry (AMS). The goal of the work is to improve our ability to determine groundwater residence times based on 14C measurements of the DOC fraction in groundwater. Water samples were collected from carbonate and volcanic rock aquifers in southern Nevada. Multiple measurements of total dissolved organic carbon (TDOC) in groundwater from one site are used to demonstrate the reproducibility of the analytical procedure. The reproducibility of the method is about one percent (1sigma) for a 0.5 mg sample. The procedural blank for the same size sample contains about 1 percent modern carbon (pMC).
    • Stepped-Combustion 14C Dating of Sediment: A Comparison with Established Techniques

      McGeehin, Jack; Burr, George S.; Jull, A. J. Timothy; Reines, D.; Gosse, J.; Davis, P. T.; Muhs, D.; Southon, John R. (Department of Geosciences, The University of Arizona, 2001-01-01)
    • The Chemical and Enzymatic Hydrolysis of Archaeological Wood Cellulose and Monosaccharide Purification by High pH Anion Exchange Chromatography for Compound-Specific Radiocarbon Dating

      Hodgins, Gregory L.; Butters, T. D.; Bronk Ramsey, Christopher; Hedges, Robert E. M. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Preliminary experiments were carried out on archaeological wood to investigate methods of cellulose hydrolysis and carbohydrate monomer purification for the purpose of compound-specific radiocarbon dating. The Chelford log, a known 14C dead source of wood cellulose, was selected for study in order to investigate the levels of contamination introduced during sample purification. Two methods of hydrolysis were examined, mineral acid hydrolysis and enzyme hydrolysis using cellulase from Penicillium funiculosum. Under the conditions described, enzymolysis was far superior to acid hydrolysis in terms of the glucose monomer yield. Glucose monomer purification was accomplished using high pH anion exchange chromatography with pulsed amperometric detection. This high performance liquid chromatography (HPLC) method does not require sample derivatization and the chromatography products can be collected in water. These characteristics make it potentially well suited to carbon dating applications. 14C dating of chromatographically purified glucose fractions revealed significant levels of contamination had accumulated during both protocols. Glucose contamination from the cellulase enzyme preparation was a major source of contamination within the enzymatically hydrolyzed samples. Ultrafiltration of the enzyme removed some but not all of this contamination. The contamination must be reduced 10-fold before the methodology could be viable for dating. This hydrolysis/HPLC method is also being investigated for 14C dating of other carbohydrate polymers such as chitin.
    • The Filling of Gaps in Geophysical Time Series by Artificial Neural Networks

      Dergachev, Valentin A.; Gorban, A. N.; Rossiev, A. A.; Karimova, L. M.; Kuandykov, E. V.; Makarenko, G. G.; Steier, Peter (Department of Geosciences, The University of Arizona, 2001-01-01)
      Nowadays, there is a large number of time series of natural data to study geophysical and astrophysical phenomena and their characteristics. However, short length and data gaps pose a substantial problem for obtaining results on properties of the underlying physical phenomena with existing algorithms. Using only an equidistant subset of the data with coarse steps leads to loss of information. We present a method to recover missing data in time series. The approach is based on modeling the time series with manifolds of small dimension, and it is implemented with the help of neural networks. We applied this approach to real data on cosmogenic isotopes, demonstrating that it could successfully repair gaps where data was purposely left out. Multi-fractal analysis was applied to a true radiocarbon time series after recovering missing data.
    • The Future of the Past

      Hedges, Robert E. M. (Department of Geosciences, The University of Arizona, 2001-01-01)
    • 'Wiggle Matching’ Radiocarbon Dates

      Bronk Ramsey, Christopher; van der Plicht, Johannes; Weninger, B. (Department of Geosciences, The University of Arizona, 2001-01-01)
      This paper covers three different methods of matching radiocarbon dates to the "wiggles" of the calibration curve in those situations where the age difference between the 14C dates is known. These methods are most often applied to tree-ring sequences. The simplest approach is to use a classical Chi-squared fit of the 14C data to the 14C curve. This gives the calendar date where the data fit best and allows tests of how good the fit is. The only drawback of this method is that it is difficult to ascertain the uncertainty in the date found in this way. An extension of this technique uses a Monte-Carlo simulation to sample possible 14C concentrations consistent with the measurement made and for each of these possibilities performs a Chi-squared fit. This method yields a distribution of values in the calendrical time-scale, from which the overall dating uncertainty can be derived. A third, rather different approach, based on Bayesian statistics, calculates the relative likelihood of each possible calendar year fit. This can then be used to calculate a range of most likely dates in a similar way to the probability method of 14C calibration. The theories underlying all three methods are discussed in this paper and a comparison made for the fitting of specific model sequences. All three methods are found to give consistent results and the application of any one of them depends on the nature of the scientific question being addressed.