• Carbonate 14C Background: Does It Have Multiple Personalities?

      Nadeau, Marie-Josée; Grootes, Pieter M.; Voelker, Antje; Bruhn, Frank; Oriwall, Alexander (Department of Geosciences, The University of Arizona, 2001-01-01)
      Measurements of the radiocarbon concentration of several carbonate background materials, either mineral (IAEA C1 Carrara marble and Icelandic double spar) or biogenic (foraminifera and molluscs), show that the apparent ages of diverse materials can be quite different. Using 0.07 pMC obtained from mineral samples as a processing blank, the results from foraminifera and mollusc background samples, varying from 0.12 to 0.58 pMC (54.0–41.4 ka), show a species-specific contamination that reproduces over several individual shells and foraminifera from several sediment cores. Different cleaning attempts have proven ineffective, and even stronger measures such as progressive hydrolization or leaching of the samples prior to routine preparation, did not give any indication of the source of the contamination. In light of these results, the use of mineral background material in the evaluation of the age of older unknown samples of biogenic carbonate (>30 ka) proves inadequate. The use of background samples of the same species and provenance as the unknown samples is essential, and if such material is unavailable, generic biogenic samples such as mixed foraminifera samples should be used. The description of our new modular carbonate sample preparation system is also introduced.
    • Chemical Removal of Conservation Substances By 'Soxhlet'-Type Extraction

      Bruhn, Frank; Duhr, Alexander; Grootes, Pieter M.; Mintrop, Annette; Nadeau, Marie-Josée (Department of Geosciences, The University of Arizona, 2001-01-01)
      At the Leibniz radiocarbon lab, art and archaeological objects, often chemically conserved and thus potentially contaminated with respect to their 14C content, are treated using a computer-controlled “Soxhlet”-type series extractor. This device uses a continuous procedure of boiling and condensation of different solvents for extraction and vacuum filtration under constant process conditions. An elutrope sequence of five solvents that dissolve most customary conservation chemicals was selected. A study of these different contaminants applied to reference wood samples with subsequent accelerator mass spectrometry (AMS) measurements demonstrates that their effective removal is dependent on the use of adequate solvents. For many contaminants (e.g. Wood glue, methyl cellulose, Klucel(R), sugar, and polyethylene glycol), routine acid-alkali-acid (AAA) treatment already yields satisfactory results, whereas for Caparol(R) and beeswax a relatively “mild” treatment with acetone, methanol, water, and subsequent standard AAA extraction is sufficient. Complete removal of rubber glue, epoxyresin, and paraffin can only be accomplished with our full set of solvents. The latter procedure is also appropriate when no or only incomplete information about the type of conservation material is available. For epoxy resin the contamination appears to be enriched in the alkali residue, and the easily soluble “humic acid” fraction, even after standard AAA treatment, gives satisfactory results. Two case studies on the application of the extraction procedures are presented.
    • Conference Participants

      Department of Geosciences, The University of Arizona, 2001-01-01
    • Converting AMS Data to Radiocarbon Values: Considerations and Conventions

      McNichol, A. P.; Jull, A. J. T.; Burr, G. S. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We summarize the basic operation of accelerator mass spectrometry (AMS) systems used to measure radiocarbon and discuss the calculations used to convert AMS output to 14C data.
    • Cosmic Background Reduction in the Radiocarbon Measurement By Scintillation Spectrometry at the Underground Laboratory of Gran Sasso

      Plastino, Wolfango; Kaihola, Lauri; Bartolomei, Paolo; Bella, Francesco (Department of Geosciences, The University of Arizona, 2001-01-01)
      Radiocarbon measurements by two 1220 Quantulus(TM) ultra low background liquid scintillation spectrometers were performed at the underground laboratory of Gran Sasso and the Radiocarbon Laboratory of E.N.E.A.-Bologna to study the efficiency and background variations related to measurement sites. The same configuration setup, i.e. The same center of gravity of the 14C spectrum (SQP(I) = 410 +/1) was obtained in both instruments. Many different background and modern standards with pure analytical benzene were used and spectra for 40 one-hour periods were obtained. The data indicates a background reduction of approximately 65% between the surface and underground laboratories, with no differences in the efficiency. Recording similar efficiencies in both spectrometers is probably due to fairly identical photomultiplier characteristics. The cosmic noise reduction observed at the laboratory of Gran Sasso makes it possible to perform high precision 14C measurements and to extend for these idealized samples the present maximum dating limit from 58,000 BP to 62,000 BP (5 mL, 3 days counting).
    • Dating of Cremated Bones

      Lanting, J. N.; Aerts-Bijma, A. T.; van der Plicht, J. (Department of Geosciences, The University of Arizona, 2001-01-01)
      When dating unburnt bone, bone collagen, the organic fraction of the bone, is used. Collagen does not survive the heat of the cremation pyre, so dating of cremated bone has been considered impossible. Structural carbonate in the mineral fraction of the bone, however, survives the cremation process. We developed a method of dating cremated bone by accelerator mass spectrometry (AMS), using this carbonate fraction. Here we present results for a variety of prehistoric sites and ages, showing a remarkable success rate for this method.
    • Delta-R Correction Values for the Northern Indian Ocean

      Dutta, Koushik; Bhushan, Ravi; Somayajulu, B. L. K. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Apparent marine radiocarbon ages are reported for the northern Indian Ocean region for the pre-nuclear period, based on measurements made in seven mollusk shells collected between 1930 and 1954. The conventional 14C ages of these shells range from 693 +/44 to 434 +/51 BP in the Arabian Sea and 511 +/34 to 408 +/51 BP in the Bay of Bengal. These ages correspond to mean Delta-R correction values of 163 +/30 yr for the northern Arabian Sea, 11 +/35 yr for the eastern Bay of Bengal (Andaman Sea) and 32 +/20 yr for the southern Bay of Bengal. Contrasting reservoir ages for these two basins are most likely due to differences in their thermocline ventilation rates.
    • Dendrochronology and Radiocarbon Dating Methods in Archaeological Studies of Scythian Sites

      Dergachev, Valentin A.; Vasiliev, S. S.; Sementsov, A. A.; Zaitseva, Ganna I.; Chugunov, K. A.; Sljusarenko, I. Ju (Department of Geosciences, The University of Arizona, 2001-01-01)
      We propose a new method of cross-dating the wood samples based on the classical methods of spectral estimation. This method uses the average cross-spectral density as a function of the relative position of the series. Because it is not sensitive to phase shifts in data it is appropriate for cross-dating samples originating from geographically distinct areas. The accuracy of cross dating depends on the integrity of the samples used, and in the case of well-preserved wood samples, the precision of relative age comparison may reach a single year. The method was tested on two dendrochronological series from Scythian barrows of known age in Southern Siberia: the Pazyryk barrows (the Altai Mountains) and the Dogee-Baary -2 burials (Western Sayan Mountains) separated by 450 km. The analysis has shown that the Pazyryk barrow is younger by 80 +/4 yr than the Dogee-Baary -2 burials. This result is in agreement with the new chronology of Scythian-related sites suggested for Southern Siberia and Central Asia.
    • Development of a Semi-Automated System for Routine Preparation of Carbonate Samples

      Tisnérat-Laborde, N.; Poupeau, J. J.; Tannau, J. F.; Paterne, M. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We constructed a semi-automated system to transform carbonate samples to CO2, as a means to increase sample-processing capacity. The physicochemical process includes hydrolysis of carbonate, quantification of the mass of carbon and CO2 collection in a glass ampoule. The system is computer-controlled and monitored, and all the data are stored. A single run of five consecutive samples requires about 3.5 hours. Measurements of 14C concentrations were made on samples of IAEAC-1 Carrara marble to test the reliability of this semi-automated system. These measurements have allowed the determination of the total system background and the memory effect of our 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.
    • Editorial Board

      Department of Geosciences, The University of Arizona, 2001-01-01
    • From the Guest Editor

      Carmi, Israel (Department of Geosciences, The University of Arizona, 2001-01-01)
    • Is Classical Acid-Alkali-Acid Treatment Responsible for Contamination? An Alternative Proposition

      Hatté, Christine; Morvan, Jean; Noury, Claude; Paterne, Martine (Department of Geosciences, The University of Arizona, 2001-01-01)
      It is well known that, during the widely used AAA pretreatment (de Vries and Barendsen 1954), alkali treatment is responsible for the incorporation of modern carbon due to the precipitation of atmospheric CO2 as carbonate. Until now, the last step of the experiment, consisting in acid treatment (most of the time with hydrochloric acid) was considered to be sufficient to eliminate all of lab contamination. But wood, peat and sediment present a complex molecular structure. During radiocarbon chemical treatments, functional groups still present in the molecules are likely to form ionic bonds with “modern” carbonates. These new chemical bonds resist a “classical” acid treatment and are responsible for rejuvenation. This short paper presents preliminary results for two common 14C cases: rejuvenation of a 0.4 pMC wood and of an Oxygen Isotope Stage 3 (OIS3) paleosol. For both cases, contamination due to incorporation of modern carbon during chemical treatment is evaluated and an alternative protocol is proposed.
    • Is Comparability of 14C Dates an Issue?: A Status Report on the Fourth International Radiocarbon Intercomparison

      Bryant, C.; Carmi, I.; Cook, G. T.; Gulliksen, S.; Harkness, D. D.; Heinemeier, J.; McGee, E.; Naysmith, P.; Possnert, G.; Scott, E. M.; et al. (Department of Geosciences, The University of Arizona, 2001-01-01)
      For more than 15 years, the radiocarbon community has participated in a series of laboratory intercomparisons in response to the issue of comparability of measurements as perceived within the wider user communities (Scott et al. 1990; Rozanski et al. 1992; Gulliksen and Scott 1995; Scott et al. 1997). In this report, we provide an update on the current 14C laboratory intercomparison and reflect on future issues linked to the laboratory intercomparison program, not least those resulting from a significant growth in the number of accelerator mass spectrometry (AMS) facilities providing routine dating of small samples (milligram size).
    • 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.
    • New Methods and Critical Aspects in Bayesian Mathematics for 14C Calibration

      Steier, Peter; Rom, Werner; Puchegger, Stephan (Department of Geosciences, The University of Arizona, 2001-01-01)
      The probabilistic radiocarbon calibration approach, which largely has replaced the intercept method in 14C dating, is based on the so-called Bayes' theorem (Bayes 1763). Besides single-sample calibration, Bayesian mathematics also supplies tools for combining 14C results of many samples with independent archaeological information such as typology or stratigraphy (Buck et al. 1996). However, specific assumptions in the "prior probabilities", used to transform the archaeological information into mathematical probability distributions, may bias the results (Steier and Rom 2000). A general technique for guarding against such a bias is "sensitivity analysis", in which a range of possible prior probabilities is tested. Only results that prove robust in this analysis should be used. We demonstrate the impact of this method for an assumed, yet realistic case of stratigraphically ordered samples from the Hallstatt period, i.e. The Early Iron Age in Central Europe.
    • Northwest Pacific Marine Reservoir Correction Estimated from Annually Banded Coral from Ishigaki Island, Southern Japan

      Hideshima, Shinichiro; Matsumoto, Eiji; Abe, Osamu; Kitagawa, Hiroyuki (Department of Geosciences, The University of Arizona, 2001-01-01)
      We assessed marine reservoir age R(t) for the costal area of the northwest Pacific using radiocarbon measurements of the annually banded coral core (Porites sp) collected on Ishigaki Island in southern Japan. Reservoir age R(t) during the early 1900s at the Pacific coast of Ishigaki Island ranged between 290 and 455 14C yr, with a weighted mean of 355 +/25 14C yr (n=5, +/1 sigma). The regional-specific ∆R, defined as 14C age difference of regional and world ocean surface layer, was 35 +/25 14C yr (n=5, +/1 sigma) on average and increased between 1900 and 1950.
    • Preliminary Estimate of the Reservoir Age in the Lagoon of Venice

      Zoppi, Ugo; Albani, A.; Ammerman, A. J.; Hua, Quan; Lawson, E. M.; Serandrei Barbero, R. (Department of Geosciences, The University of Arizona, 2001-01-01)
      The Lagoon of Venice was formed about 6000 years ago due to the marine transgression associated with the late Pleistocene sea level rise. Already by the time of the Republic of Venice (727-1797 AD) it was recognized that the future of the city and its many historical buildings was strongly correlated with the future of the lagoon itself. During the centuries many engineering projects such as modification of the fluvial systems, construction of coastal barriers, and dredging of navigation channels were carried out to preserve the lagoonal environment. The present-day lagoon is the result of all these processes and covers an area of 540 km2 with an average depth of 0.6 m. A series of radiocarbon age determinations carried out on material obtained from cores collected in the Lagoon of Venice indicate within the sedimentary units the existence of a number of discontinuities and slumping events due to the highly active lagoonal environment. The evaluation of data obtained from a variety of different materials—both terrestrial and marine—allowed us to determine for the first time the marine reservoir effect in the lagoon of Venice. The discussion includes a comparison with other relevant measurements and a possible explanation to the relatively high reservoir age (1200-1300 yr).
    • 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.
    • Pretreatment of Iron Artifacts at SNU-AMS

      Cheoun, M. K.; Kim, J. C.; Kang, J.; Kim, I. C.; Park, J. H.; Song, Y. M. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We present the current status of accelerator mass spectrometry (AMS) dating of iron artifacts at Seoul National University (SNU). In ancient iron production, charcoal was widely used as carbon for the smelting process, whereas coal is used in modern times. If reliable data could be obtained from carbon by using AMS, ancient iron artifacts could be traced to their production age. In normal acid treatment, it is not easy to extract carbon due to its colloidal property. The negative charge property of the carbon colloid, however, makes it possible for it to be precipitated with positive ions by dissolving the iron chemically. An extraction yield of the carbon incorporated in modern cast iron of about 70% is attained. More refined methods to increase the extraction rate are under progress for archaeological applications.