• First 14C Results from Archaeological and Forensic Studies at the Vienna Environmental Research Accelerator

      Wild, Eva; Golser, Robin; Hille, Peter; Kutschera, Walter; Priller, Alfred; Puchegger, Stephan; Rom, Werner; Steier, Peter; Vycudilik, W. (Department of Geosciences, The University of Arizona, 1998-01-01)
      14C dating with the new Vienna Environmental Research Accelerator (VERA) began with the age determination of a mummified marmot found in the Austrian Alpine region. Soft tissue and bones of the marmot were used for the investigation. For comparison, bone material from known-age samples was also processed and measured. These exercises showed that 14C dating with VERA is reliable, and since that time various samples from archaeological context have been dated. We also studied the applicability of the 14C method in forensic sciences to determine the time of death of human individuals. 14C/ 12C measurements of samples from different organic human material (bone collagen, lipids from bone and bone marrow, hair) were performed and compared with the tropospheric "bomb peak" values to transform the measured ratios into "calibrated ages". For specific substances with rapid turnover rates, this gives an estimate for the time of death of the individual. In our study, lipids and hair yield reasonable times of death, whereas the collagen fraction from bones, which has a relatively long turnover time, is not suitable for this purpose.
    • On the Validity of the Poisson Hypothesis for Low-Level Counting: Investigation of the Distributional Characteristics of Background Radiation with the NIST Individual Pulse Counting System

      Currie, L. A.; Eijgenhuijsen, E. M.; Klouda, G. A. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Does radioactive decay follow the Poisson distribution?—a fundamental question, to which the theoretical answer seems to be, Yes. On the practical side, the answer to this question impacts the best achievable precision in well-controlled counting experiments. There have been some noteworthy experimental tests of the Poisson assumption, using systems carefully designed for the analysis of individual pulses from stable radioactive sources; thus far, experiment supports theory. For low-level counting, the nature of the background distribution can be of profound practical importance, especially for very long counting experiments where validation by an adequate number of full replicates may be impracticable. One is tempted in such cases to assume that the variance is equal to the mean, in order to estimate the measurement uncertainty. Background radiation, however, has multiple components, only some of which are governed by the laws of radioactive decay. A specially designed low-level gas counting system at NIST for interactive, retrospective individual pulse shape and time series analysis makes possible the investigation of the empirical distribution function of the background radiation, in a manner similar to the previous empirical distribution studies of radioactive decay. Benefits of individual pulse analysis are that there is no information loss due to averaging and that two independent tests of the Poisson hypothesis can be performed using data from a single, extended measurement period without the need for replication; namely, tests of the distribution of arrival times, expected to be uniform, and the distribution of inter-arrival times, expected to be exponential. For low-level counting the second test has a very interesting and very informative complement: the distribution of coincidence-anticoincidence inter-arrival times. Key outcomes from the study were that: 1) nonstationarity in the mean background rate over extended periods of time could be compensated by an on-line paired counter technique, which is far preferable to the questionable practice of using an "error-multiplier" that presumes the wandering (nonstationary) background to be random; and 2) individual empirical pulse distributions differed from the ideal GM and Poisson processes by exhibiting giant pulses, a continuum of small pulses, afterpulses, and in certain circumstances bursts of pulses and transient relaxation processes. The afterpulses constituted ca. 8% of the anti-coincidence background events, yet they escaped detection by the conventional distributional tests.
    • Methodological Issues in the 14C Dating of Rock Paintings

      Hedges, R. M.; Bronk Ramsey, Christopher; Van Klinken, G. J.; Pettitt, P. B.; Nielsen-Marsh Christina; Etchegoyen, Alberto; Fernandez Niello, J. O.; Boschin, M. T.; Llamazares, A. M. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Chemical and isotopic analyses have been made of pigment samples from two separate rock art sites in Argentina. The purpose of the study has been to establish the feasibility of extracting carbonaceous material from the samples which will permit reliable radiocarbon dates for the time of painting. The two sites, Catamarca and Rio Negro, present quite different problems. Most of the paper is concerned with Catamarca, and here we have shown that the paint pigments contain very little or no organic binder; but they do contain calcium oxalate derived from local cacti, and calcium carbonate derived probably from local plant ash. We describe a method to purify carbon extracted from the calcium oxalate, and present the dates obtained on both components. We show that, though rare, natural deposits containing both calcium oxalate and calcite do occur, but that they are very distinct in both 13C and 14C compositions; and we argue that they are very unlikely to contaminate the pigments to such an extent that the 14C dates are altered. For the Rio Negro site we show that the ground for the paint pigments contains carbon derived from fires burnt inside the cave, and discuss how analytical methods provide information to develop a strategy for extracting material, from both ground and pigment, for more reliable dating.
    • The Carbonate 14C Background and Its Components at the Leibniz AMS Facility

      Schleicher, Markus; Grootes, Pieter M.; Nadeau, Marie-Josée; Schoon, Axel (Department of Geosciences, The University of Arizona, 1998-01-01)
      After routine accelerator mass spectrometry (AMS) radiocarbon dating had been established at the Leibniz-Labor with the completion of systems for CO2 production, graphitization, and target making, a systematic investigation was conducted to find the sources of 14C concentrations observed in background materials. We quantified the contributions of the AMS-system, the reduction, CO2 production from carbonate, carbonate contamination, and combustion. Carbonate contamination appears to be the dominating factor. Improvements in the pretreatment of foraminifer carbonate have led to the elimination of most of this contamination.
    • The Behavior of Sellafield-Derived 14C in the Northeast Irish Sea

      Wolstenholme, Anne; Cook, G. T.; MacKenzie, A. B.; Naysmith, Philip; Meadows, P. S.; McDonald, Paul (Department of Geosciences, The University of Arizona, 1998-01-01)
      Radiocarbon is an important constituent of the low level, liquid, radioactive effluent discharged from the Sellafield nuclear fuel reprocessing plant in northwest England, but despite the fact that it gives the highest collective dose commitment of all the nuclides in the waste, its behavior in the Irish Sea is poorly defined. There is therefore a clear requirement for an improved understanding of 14C behavior in the Irish Sea, to assist with dose evaluation modeling and definition of the mixing and accumulation characteristics of the sediment in this area. In this context, results are presented here for a temporal study of 14C activities in four geochemical fractions of seawater and in a sediment core from the vicinity of the Sellafield effluent outfall. Clear 14C enrichments in the dissolved inorganic carbon (DIC) and particulate organic carbon (POC) components of seawater were observed, with temporal trends in activity that were related to variations in the Sellafield discharge. Smaller, but nevertheless detectable, enrichments were also observed for particulate inorganic carbon (PIC) and dissolved organic carbon (DOC) in the seawater. The distribution of 137Cs and 241Am revealed that the sediment core could be classified into three zones in which the intensity of mixing decreased discontinuously with depth. Bulk carbonate 14C analyses of the core demonstrated the presence of glacial or pre-glacial carbonate in the system, but failed to show any evidence of contaminant 14C input or provide information on sediment accumulation processes. In contrast, analysis of bulk organic matter from the sediment provided clear evidence of the recent perturbation of a well mixed system by input of younger material, consistent with the recent input of contaminant 14C from Sellafield and possibly weapons testing fallout.
    • New 14C Reference Materials with Activities of 15 and 50 pMC

      Le Clercq, Martijn; van der Plicht, Johannes; Gröning, Manfred (Department of Geosciences, The University of Arizona, 1998-01-01)
      Two new 14C reference materials have been developed for international use, filling a gap in the present C1-C6 series available from the IAEA. By mixing a modern and a synthetic substance, 150 kg of C7 (ca. 50 pMC activity) and C8 (ca. 15 pMC activity), respectively, were obtained.
    • The Erlangen AMS Facility and Its Applications in 14C Sediment and Bone Dating

      Kretschmer, W.; Anton, G.; Benz, M.; Blasche, S.; Erler, G.; Finckh, E.; Fischer, L.; Kerscher, H.; Kotva, A.; Klein, M.; et al. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We report here on the radiocarbon dating of sediment samples from Bavaria using the Erlangen accelerator mass spectrometry facility. The absolute time calibration of different sediment profiles, together with pollen analyses, should establish a better chronology of climate and vegetation during Holocene in Bavaria. For an enhanced reliability of sediment dating, we measured different fractions such as bulk sediments, pollen grains, macrofossils and humic acids. For these fraction, we describe the separation methods and conversion to sputter targets. Furthermore, we discuss the sample preparation for the dating of bones and present some results.
    • Microscale AMS 14C Measurement at NOSAMS

      Pearson, Ann; McNichol, Ann P.; Schneider, Robert J.; Von Reden, K. F.; Zheng, Yan (Department of Geosciences, The University of Arizona, 1998-01-01)
      Techniques for making precise and accurate radiocarbon accelerator mass spectrometry (AMS) measurements on samples containing less than a few hundred micrograms of carbon are being developed at the NOSAMS facility. A detailed examination of all aspects of the sample preparation and data analysis process shows encouraging results. Small quantities of CO2 are reduced to graphite over cobalt catalyst at an optimal temperature of 605 degrees C. Measured 14C/12C ratios of the resulting targets are affected by machine-induced isotopic fractionation, which appears directly related to the decrease in ion current generated by the smaller sample sizes. It is possible to compensate effectively for this fractionation by measuring samples relative to small standards of identical size. Examination of the various potential sources of background 14C contamination indicates that the sample combustion process is the largest contributor, adding ca. 1 micrograms of carbon with a less-than-modern 14C concentration.
    • The Effect of a Succession of Ocean Ventilation Changes on 14C

      Stocker, Thomas F.; Wright, Daniel G. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Using the model of Stocker and Wright (1996), we investigate the effect of a succession of ocean ventilation changes on the atmospheric concentration of radiocarbon, Delta-14C(atm), the surface reservoir ages, the top-to-bottom age differences, and the calendar-14C age relationships in different regions of the ocean. The model includes a representation of the cycling of 14C through the atmosphere, the ocean and the land biosphere. Ocean ventilation changes are triggered by increasing rates of freshwater discharge into the North Atlantic, which are determined according to a simple feedback mechanism between the melting rates and the climatic state of the North Atlantic region. The results demonstrate that ventilation changes can cause Delta-14C(atm) fluctuations of 25%, surface reservoir age fluctuations of 100 yr in the Pacific (200 yr in the Atlantic) and top-to-bottom age variations of 500 yr in the Pacific (1000 yr in the Atlantic). We also show that 14C age estimates based on marine organisms that live in the near-surface region of the ocean and take up the signal of surface 14C can result in apparent age reversals if the assumption of a constant reservoir age is made.
    • The Influence of Pretreatment on Humic Acid Yield and 14C Age of Carex Peat

      Cook, G. T.; Dugmore, A. J.; Shore, J. S. (Department of Geosciences, The University of Arizona, 1998-01-01)
      The object of the study was to assess the effects of a range of pretreatment/extraction schemes on the yields of humic acid and humin obtained from peat and the subsequent radiocarbon ages. We analyzed peat from Flokadalur in northern Iceland, collecting material from a profile containing seven visible tephra horizons in the upper 3 m, whose form and extent indicated little disturbance to the section over the last 4000 yr. The results of a range of pretreatments demonstrated that time rather than the strength of alkali is the more important factor governing the extraction of humic acid. An increase in alkali molarity did not correspond to any systematic increase in yield, whereas an increase in time did, implying that the extraction is kinetically controlled. We found no evidence of variability in 14C age due to pretreatment scheme or between different geochemical fractions of the peat. Further implications from this study are that bog stability and ecological simplicity produce a favorable environment for 14C dating.
    • The New Nagoya Radiocarbon Laboratory

      Muraki, Yasushi; Kocharov, Grant E.; Nishiyama, Tooru; Naruse, Yukiko; Murata, Takuya; Masuda, Kimiaki; Arslanov, Kh A. (Department of Geosciences, The University of Arizona, 1998-01-01)
      A liquid scintillation counting apparatus that enables highly accurate measurements of 14C has been constructed at the Solar-Terrestrial Environment Laboratory, Nagoya University. The main aim of the project is high precision year-by-year measurements of the 14C content in tree rings of an old cedar tree from Yaku Island, Japan. We present the results of 14C measurements on tree rings from the Agematsu region for recent decades to confirm the validity of the system.
    • Performance of the Packard Tri-Carb(R) 2770TR/SL Liquid Scintillation Analyzer for 14C Dating

      Passo, C. J.; Anderson, Robert; Roberts, David; Cook, G. T. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We present results that demonstrate the potential of the Packard Tri-Carb(R) Model 2770TR/SL for radiocarbon dating. For 2 g of sample benzene, a stable background count rate of 0.307 cpm and a stable counting efficiency of 64.78% were determined using a 13-75 keV counting window. Changes to the mathematical routines for t-SIE (quench indicating parameter) calculation and a reduction in the activity of the external standard have enabled stability of the t-SIE to be achieved, and combined with the use of a suitable balance point counting window; all of these factors give the stability of performance required for 14C dating. Calculations based on the above parameters indicate that the limit of detection for 2 g samples, counted for 5000 min, is <48,900 yr BP. The great advantage of this system is that these data were acquired using inexpensive standard 7-mL low potassium borosilicate glass vials. Vial holders manufactured from BGO reduced the background to 0.15 cpm with a minimum effect on efficiency (64.46% for 13-75 keV). A similar calculation of the limit of detection gave >51,700 BP. The use of the BGO vial holders in other instruments employing time-resolved liquid scintillation counting (TR-LSC) (Models 2250CA and 2260XL) also brought about significant improvements in detection limits.
    • The Pursuit of Isotopic and Molecular Fire Tracers in the Polar Atmosphere and Cryosphere

      Currie, L. A.; Dibb, J. E.; Klouda, G. A.; Benner, B. A.; Conny, J. M.; Biegalski, Steven R.; Klinedinst, Donna B.; Cahoon, Donald R.; Hsu, N. C. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We present an overview of recent multidisciplinary, multi-institutional efforts to identify and date major sources of combustion aerosol in the current and paleoatmospheres. The work was stimulated, in part, by an atmospheric particle "sample of opportunity" collected at Summit, Greenland in August 1994, that bore the 14C imprint of biomass burning. During the summer field seasons of 1995 and 1996, we collected air filter, surface snow and snowpit samples to investigate chemical and isotopic evidence of combustion particles that had been transported from distant fires. Among the chemical tracers employed for source identification are organic acids, potassium and ammonium ions, and elemental and organic components of carbonaceous particles. Ion chromatography, performed by members of the Climate Change Research Center (University of New Hampshire), has been especially valuable in indicating periods at Summit that were likely to have been affected by the long range transport of biomass burning aerosol. Univariate and multivariate patterns of the ion concentrations in the snow and ice pinpointed surface and snowpit samples for the direct analysis of particulate (soot) carbon and carbon isotopes. The research at NIST is focusing on graphitic and polycyclic aromatic carbon, which serve as almost certain indicators of fire, and measurements of carbon isotopes, especially 14C, to distinguish fossil and biomass combustion sources. Complementing the chemical and isotopic record, are direct "visual" (satellite imagery) records and less direct backtrajectory records, to indicate geographic source regions and transport paths. In this paper we illustrate the unique way in which the synthesis of the chemical, isotopic, satellite and trajectory data enhances our ability to develop the recent history of the formation and transport of soot deposited in the polar snow and ice.
    • The Sharp Rise of Delta-14C ca. 800 cal BC: Possible Causes, Related Climatic Teleconnections and the Impact on Human Environments

      Van Geel, Bas; van der Plicht, Johannes; Kilian, M. R.; Klaver, E. R.; Kouwenberg, J. M.; Renssen, H.; Reynaud-Farrera, I.; Waterbolk, H. T. (Department of Geosciences, The University of Arizona, 1998-01-01)
      In this study we report on accelerator mass spectrometry (AMS) wiggle-match dating of selected macrofossils from organic deposits ca. 800 cal BC (ca. 2650 BP). Based on paleological, archaeological and geological evidence, we found that the sharp rise of atmospheric 14C between 850 and 760 cal BC corresponds to the following related phenomena: 1. In European raised bog deposits, the changing spectrum of peat forming mosses and a sharp decline in decomposition of the peat indicate a sudden change from relatively dry and warm to cool, moist climatic conditions. 2. As a consequence of climate change, there was a fast and considerable rise of the groundwater table so that peat growth started in areas that were already marginal from a hydrological point of view. 3. The rise of the groundwater table in low-lying areas of the Netherlands resulted in the abandonment of settlement sites. 4. The contemporaneous earliest human colonization of newly emerged salt marshes in the northern Netherlands (after loss of cultivated land) may have been related to thermal contraction of ocean water, causing a temporary stagnation in the relative sea-level rise. Furthermore, there is evidence for synchronous climatic change in Europe and on other continents (climatic teleconnections on both hemispheres) ca. 2650 BP. We discuss reduced solar activity and the related increase of cosmic rays as a cause for the observed climatological phenomena and the contemporaneous rise in the 14C-content of the atmosphere. Cosmic rays may have been a factor in the formation of clouds and precipitation, and in that way changes in solar wind were amplified and the effects induced abrupt climate change.
    • The Tunguska Event as Recorded in a Tree Trunk

      Yonenobu, Hitoshi; Takenaka, Chisato (Department of Geosciences, The University of Arizona, 1998-01-01)
      A living spruce tree was collected near the explosion center of the Tunguska event that occurred in 1908. We measured annual ring width and studied anatomical features to reconstruct the possible vegetational changes caused by the biological aftereffects of the Tunguska explosion. Delta-14C of annual rings from 1908 to 1910 was measured with a Tandetron accelerator mass spectrometer. The annual ring width decreased rapidly in 1908-1912, drastically increased in 1913, and decreased gradually thereafter. Traumatic resin ducts were observed in the transition zone between earlyand latewood of the annual ring formed in 1908. We thus reconstruct these vegetational changes in the Tunguska forest: the Tunguska explosion damaged forest trees severely for ca. 3 yr, releasing rich nutrients from burned plants into the soil, and subsequently the vegetation was stimulated to recover by decreased socio-biological competition and better lighting conditions. Delta-14C values range from -28.2 to -1.5 per mil for Tunguska spruce, and from -29.7 to 12.6 per mil for Hinoki cypress. These fluctuations are within the ranges presented in Stuiver and Becker (1993), suggesting no evidence of anomalies of cometary origin in carbon isotopic composition. We found no significant difference between Delta-14C of Tunguska spruce and of Hinoki cypress.
    • Probability and Dating

      Bronk Ramsey, Christopher (Department of Geosciences, The University of Arizona, 1998-01-01)
      Statistical analysis is becoming much more widely used in conjunction with radiocarbon dating. In this paper I discuss the impact of Bayesian analysis (using computer programs such as OxCal) on archaeological research. In addition to simple analysis, the method has implications for the planning of dating projects and the assessment of the reliability of dates in their context. A new formalism for describing chronological models is introduced here: the Chronological Query Language (CQL), an extension of the model definitions found in the program OxCal. New methods of Bayesian analysis can be used to overcome some of the inherent biases in the uncertainty estimates of scientific dating methods. Most of these methods, including 14C, uranium series and thermoluminescence (TL), tend to favor some calendar dates over others. 14C calibration overcomes the problem where this is possible, but a Bayesian approach can be used more generally.
    • 14C Cycle in the Hot Zone Around Chernobyl

      Kovaliukh, Nikolai N.; Skripkin, Vadim V.; van der Plicht, Johannes (Department of Geosciences, The University of Arizona, 1998-01-01)
      Radiocarbon from the Chernobyl accident was released mainly in two forms: fine dispersed reactor graphite, and carbon dioxide from burning graphite. The CO2 was partly assimilated by annual and perennial vegetation. Reactor graphite dispersed over a wide territory was taken up biochemically by micromicetes, transforming non-organic carbon of the reactor graphite into organic matter. Organic matter of micromicetes is the main nutrition product for soil organisms such as bacteria, worms, larvae of insects, small beetles, etc. The following relatively independent trophic chains are considered: 1. Carbon dioxide —> leaves, grass —> insects; 2. Graphite —> micromicetes, protozoa, insects. The 14C content in beetles of different species sampled in the 30-km hot zone of the Chernobyl accident site in 1986-1988 agrees well with the contamination levels of insect habitats as well as with their biology.
    • Two Decades of Environmental Isotope Records in Croatia: Reconstruction of the Past and Prediction of Future Levels

      Krajcar-Bronić, Ines; Horvatinčić, Nada; Obelić, Bogomil (Department of Geosciences, The University of Arizona, 1998-01-01)
      A two-decade-long record of environmental isotopes (2H, 3H, 14C, 18O) in Croatia is presented and the data are statistically analyzed. The atmospheric 14C activity for the period before the actual measurements started is reconstructed by measuring tree rings from the clean-air sites, and the past tritium activity in precipitation is estimated by the correlation of our data with the Vienna station record. The long-term 3H record helped to determine a locally contaminated sampling site, and new clean sites are put into operation. The 14C data were fitted by an analytical function and the prediction of future levels is given assuming that the rate of the 14C releases remains constant. From the long-term stable isotope data record, the local meteoric water line and the temperature gradient of delta-18O in precipitation are determined.
    • 14C Database and Geographic Information System for Western Siberia

      Orlova, Lyobov A.; Kuzmin, Yaroslav V.; Zolnikov, Ivan D. (Department of Geosciences, The University of Arizona, 1998-01-01)
      We illustrate here the combined use of geographic information system (GIS) technology and a radiocarbon database for analysis of the environmental components and ancient sites in Western Siberia during the period 10-45 ka BP. In total, 230 14C dates from 75 Late Pleistocene outcrops and Paleolithic sites were used to generate paleolandscape maps and to establish the features of the spatiotemporal distribution of Paleolithic sites.