• Dating Polar Ice by 14C Accelerator Mass Spectormetry

      Andree, Michael; Beer, Jürg; Loetscher, H. P.; Moor, Ernst; Oeschger, Hans; Bonani, Georges; Hofmann, Hans Jakob; Morenzoni, Elvezio; Nessi, Marzio; Suter, Martin; et al. (American Journal of Science, 1986-01-01)
      Results of 14C/12C ratio measurements on CO2 extracted from air bubbles in polar ice are presented. The samples investigated originate from the Dye 3, South Greenland, deep ice core and span approximately the last 10,000 years. The results are calibrated with tree-ring records. The 14C ages are compared with information obtained from seasonal variations of ice-core parameters and rheologic model calculation.
    • Early Slavonic Settlements and Navigation at the Mouth of the Odra River

      Awsiuk, Romuald; Filipowiak, Władyslaw; Goslar, Tomasz; Pazdur, Anna; Pazdur, Mieczysław F. (American Journal of Science, 1986-01-01)
      An attempt is presented to establish an absolute chronology of early Slavonic habitation in the region of the mouth of the Odra River up to the Baltic and to find associations with a series of stave boats and dugouts of different levels of technology and navigation. The methodology of the research project is presented and some conclusions of a general nature are drawn from the results already obtained.
    • Discordant Ages Related to Reservoir Effect of Associated Archaeologic Remains from the Tunel Site, Beagle Channel, Argentine Republic

      Albero, Miguel C.; Angiolini, Fernando E.; Piana, Ernesto L. (American Journal of Science, 1986-01-01)
      Evidence of a tradition of human maritime adaptation was recovered from various sites at Beagle Channel dating back to ca 6000 yr BP. Final occupations date to European settlement in the 19th century. The Túnel site exhibits discontinuous human occupation ranging from 6000 to 500 yr BP, represented by different archaeologic remains in each layer. Associated charcoal, mollusk shells, and Lama guanicoe and Arctocephalus australis bones were dated. Shells and Arctocephalus are consistently older than charcoal, demonstrating the reservoir effect at Beagle Channel. Results encourage further work in the area to evaluate the spatial and temporal magnitude of the effect.
    • Studies of Non-Marine Mollusks for the Selection of Shell Samples for Radiocarbon Dating

      Yates, Timothy (American Journal of Science, 1986-01-01)
      14C dating of shells from terrestrial and freshwater mollusks is prone to distortion by post-depositional diagenesis as well as incorporation of material depleted in 14C while the mollusk was alive. Three types of diagenetic change can result: etching, the development of surface crusts, and replacement of aragonite by calcite. Inspection under the light microscope, x-ray diffraction, and scanning electron microscope make it possible to assess the relative importance of the changes. When they are corrfined to the surface, mechanical cleaning combined with judicious leaching can reduce them to <1% of the total sample. The corresponding errors, which can now be specified, are often no greater than those associated with the statistics of counting.
    • Dendrochronology—The Absolute Irish Standard

      Brown, D. M.; Munro, M. R.; Baillie, M. G. L.; Pilcher, J. R. (American Journal of Science, 1986-01-01)
      Since the 11th International Radiocarbon Conference considerable advances have been made in European dendrochronology giving several long continuous absolute chronologies. Recent collaboration between European laboratories provides confirmation of the accuracy of these chronologies and, thus, of the standards used for radiocarbon calibration.
    • Environmental 14C Levels Around the 632 MWe Nuclear Power Plant Krško in Yugoslavia

      Obelić, Bogomil; Krajcar-Bronić, Ines; Srdoč, Dušan; Horvatinčić, Nada (American Journal of Science, 1986-01-01)
      Measurements of 14C activity of atmospheric CO2, vegetables, and tree rings in the area of the 632 MWe power plant Krško in Slovenia, NW Yugoslavia, have been in progress since January, 1984. Sampling stations are located in the area ca 400km2 and are distributed in the direction of the prevailing westerly winds. The closest sampling point is 1.5km NE of the plant exhaust stack, the farthest sampling point is 30km E of the plant. A sampling site at National Park Plitvice in central Croatia was chosen as the 14C reference point not affected by the power plant. An average excess of 2.2% above the reference point activity during normal periods of reactor operation was observed 1.5km from the plant smokestack. Calculations of the 14C release from the power plant was estimated at 0.1 TBq/a. The tree ring activity near the plant followed the 14C activity of the Northern Hemisphere in the past decade. No influence of the power plant release was observed on the tree ring activity.
    • Carbon Isotopes in Atmospheric CO2 of the Krakow Region: A Two-Year Record

      Kuc, Tadeusz (American Journal of Science, 1986-01-01)
      We have been measuring concentration of atmospheric CO2 and its carbon isotope composition in the Kraków region for about two years. Samples are continuously collected at two-week intervals at ca 20m above ground level, close to the center of the industrialized urban area. Sampled atmospheric CO2 is sorbed in a molecular sieve and, after recovery by heating, is converted to benzene. 14C is measured in a liquid scintillation spectrometer, and delta-13C of the CO2 is determined in a mass spectrometer. The annual record shows winter-summer variation of 14C, 13C, and CO2 concentration. A long-term trend for 1983 and 1984 indicates a slight decrease of 14C activity (122.0 in January 1983; -1.2% per year), a permanent decrease of delta-13CPDB (-9.3 per mil in January 1983; -0.3 per mil per year) and an increase of CO2 concentration (344ppm in January 1983; 1.4ppm per year).
    • Carbon Cycle: 1985 Glacial to Interglacial Changes in the Operation of the Global Carbon Cycle

      Broecker, Wallace S.; Peng, Tsung-Hung (American Journal of Science, 1986-01-01)
      The hottest topic for those interested in the earth's carbon cycles is the change in atmospheric CO2 content between glacial and interglacial time. What caused it? What is its role in glacial cycles? We evaluate here the hypotheses that have been put forward to explain the CO2 change with evidence from deep sea sediments. We conclude that all the hypotheses have serious drawbacks and that much effort will have to be expended in gathering more data from ice cores and ocean sediments before we will be pointed toward the correct scenario. Also, thoughtful modeling aimed at depicting the ties between pCO2, O2, 13C/12C, 14C/12C, and nutrient constituents in the sea for various modes of circulation will have to be done before the evidence from ocean cores can be properly interpreted.
    • Optimization of Liquid Scintillation Counting for 14C Dating

      Angiolini, Fernando E.; Albero, Miguel C. (American Journal of Science, 1986-01-01)
      The effects of different measurement conditions and sample preparation in liquid scintillation counting of benzene for 14C dating were tested. The goal of this work was to find the highest figure of merit through the variation of scintillation cocktail to benzene ratio, and measurement windows. Measurements were performed on 5m1 of benzene plus increasing quantities of scintillation cocktail (7g of PPO and 0.5g of Me2POPOP in IL of scintillation-grade toluene). Spectra of both background and standard were obtained and the counting windows selected for the highest figure of merit (Q). The best condition was 5m1 of benzene plus 0.75ml of scintillation cocktail. This spectrum is compared with that of I) pure toluene-14C plus cocktail, and 2) pure benzene-14C in which the equivalent amount of PPO and Me2POPOP present in 0.75ml of cocktail was dissolved. A correlation between the increase of the aniount of cocktail and the broadening of the spectrum was observed. The effect of wrapping the upper part of the counting vial with aluminum foil to reduce background was also tested. A drastic background increment was observed in the low energy range, for unwrapped vials; the standard spectrum showed a broadening and a lower counting efficiency which reduced the figure of merit.
    • Dating of Holocene Stratigraphy with Soluble and Insoluble Organic Fractions at the Lubbock Lake Archaeological Site, Texas: An Ideal Case Study

      Haas, Herbert; Holliday, Vance; Stuckenrath, Robert (American Journal of Science, 1986-01-01)
      The Lubbock Lake site, on the Southern High Plains of Texas, contains one of the most complete and best-dated late Quaternary records in North America. A total of 117 14C dates are available from the site, determined by the Smithsonian and SMU Laboratories. Of these dates, 84 have been derived from residues (humin) and humates (humic acids) of organic-rich marsh sediments and A horizons of buried soils. Most of the ages are consistent with dates determined on charcoal and wood, and with the archaeologic and stratigraphic record. The dates on the marsh sediments are approximate points in time. Dates from the top of buried A-horizons are a maximum for burial and in many cases are close to the actual age of burial. Dates from the base of the A-horizons are a minimum for the beginning of soil formation, in some cases as much as several thousand years younger than the initiation of pedogenesis. A few pairs of dates were obtained from hurnin and humic acid derived from split samples; there are no consistencies in similarities or differences in these age pairs. It also became apparent that dates determined on samples from scraped trench walls or excavations that were left open for several years are younger than dates from samples taken from exactly the same locations when the sampling surfaces were freshly excavated.
    • Groningen 14C Data Base

      Endelsman, F. M. R.; Taayke, E.; Mook, W. G. (American Journal of Science, 1986-01-01)
    • The Temporal Distribution of 'Bomb' 14C in a Forest Soil

      Harkness, D. D.; Harrison, A. F.; Bacon, P. J. (American Journal of Science, 1986-01-01)
      Patterns of 14C enrichment in the superficial plant debris and mineral soil horizons of an established woodland have been monitored at regular intervals during the past 15 years. These data are compared with a model evaluation of carbon turnover based on the recorded changes in atmospheric 14C concentration since AD 1900. Leaf litter and decomposing plant debris are characterized by steady-state turnover values of ca 2 and ca 8 years, respectively. A two-component system of `fast' (less than or equal to 20 yr) and `slow' (ca 350 yr) cycling carbon is indicated for the surface (0-5cm) soil humus; below 10cm, the `fast' component is rare (<5%). Selective microbal humification of leaf litter, branch, and root debris is proposed to explain a delay of several years in the peak transfer of `bomb' 14C to the soil carbon pool.
    • The Use of Natural and Anthropogenic 14C to Investigate the Dynamics of Soil Organic Carbon

      O'Brien, Bernard John (American Journal of Science, 1986-01-01)
      Radiocarbon has been measured in two soil profiles, one of which has been covered by a building since 1956. A comparison of the Delta-14C values in horizons of each profile gives an estimate of the total input of atom bomb 14C into the soil profile. From the Delta-14C and carbon density profile data, the carbon input rates, respiration rates, and diffusivity are calculated. The lack of vegetation on one soil affects the mobility and the respiration rate of the soil carbon in that soil. The data from this soil profile are also used to check the assumption, used in previous analyses, that there is a uniform distribution of "old" carbon down the soil profile. The input rate, turnover time, and diffusivity parameters determined from the Delta-14C profiles in these soils are compared with other published data on pasture and forest soils.
    • Increase of 14C Activity of Dissolved Inorganic Carbon Along a River Course

      Srdoč, Dušan; Krajcar-Bronić, Ines; Horvatinčić, Nada; Obelić, Bogomil (American Journal of Science, 1986-01-01)
      Results of measurements for 3 years (1981-1983) of 14C activity of dissolved inorganic carbon (DIC) in water samples from the Korana River, as well as that of recent tufa and aquatic plants, showed that 14C concentration increases from karst spring to the estuary. A model describing the increase of 14C activity was developed assuming that the increase is due to the exchange of the dissolved CO2 in stream water with atmospheric CO2 and to dissolution of CO2 from the decay of organic material and root respiration. It is possible to distinguish these two contributions by measuring the delta-13C values of DIC in water. As expected, our data show that the exchange process between atmospheric CO2 and DIC dominates at rapids and waterfalls, while biologic contribution is much higher in lakes and along the lowland flow of the Korana River. Agreement between the calculated and the measured activities supports the proposed mechanisms of chemical and isotopic exchanges in stream waters.
    • Toward a Thesaurus of Radiocarbon Dating and Related Terms

      Polach, Dilette (American Journal of Science, 1986-01-01)
      The development of a Thesaurus of Radiocarbon Dating and Related Terms was undertaken to provide a basic common vocabulary of terms for the purpose of indexing an Annotated Bibliography of Radiocarbon Dating (1948-68) and form the basis of a language for information storage and retrieval in 14C dating and related term areas. The interdisciplinary nature of 14C dating dictates that selected terms have meanings in the context of archaeology, geology, earth sciences, oceanography, and environmental sciences, to name but a few, as well as chemistry and nuclear instrumentation on which the technique of 14C determinations is based. This paper describes the method used for selection of terms and explains the structure of the proposed thesaurus. A limited edition Draft Thesaurus was distributed to a selected panel of colleagues for critical evaluation.
    • Ice-Core Dating of the Pleistocene/Holocene Boundary Applied to a Calibration of the 14C Time Scale

      Hammer, Claus U.; Clausen, Henrik B.; Tauber, Henrik (American Journal of Science, 1986-01-01)
      Seasonal variations in 18O content, in acidity, and in dust content have been used to count annual layers in the Dye 3 deep ice core back to the Late Glacial. In this way the Pleistocene/Holocene boundary has been absolutely dated to 8770 BC with an estimated error limit of +/- 150 years. If compared to the conventional 14C age of the same boundary a value of Delta-14C = 53 +/- 13 per mil is obtained. This Delta-14C value suggests that 14C levels during the Late Glacial were not substantially higher than during the Postglacial.
    • Trends of 13C/12C Ratios in Pinyon Tree Rings of the American Southwest and the Global Carbon Cycle

      Leavitt, S. W.; Long, Austin (American Journal of Science, 1986-01-01)
      An accurate atmospheric 13C/12C chronology can provide important constraints to models of the global carbon cycle. Trees accumulate carbon from atmospheric CO2 into growth rings and offer potential for 13C/12C reconstructions, but results have not been reproducible. This paper presents 5 degree C curves from 5 sites, representing 20 pinyon (Pinus edulis) trees, where cores of 4 trees from each site have been pooled into a composite sample. Isotopic analysis of cellulose in 5-yr ring groups produces curves with a general trend of decreasing 5 degree C after 1800, but with pronounced short-term fluctuations superimposed upon the trend. Evidence indicates the fluctuations are strongly related to moisture availability (drought). A mean curve of the 5 delta-13C chronologies from which the fossil-fuel component is subtracted suggests a substantial biospheric CO2 contribution to the atmosphere since 1800.
    • Laser Resonance Ionization Mass Spectrometry for Krypton-81 Analysis

      Lehmann, B. E.; Loosli, H. H.; Oeschger, Hans; Rauber, Dominique; Hurst, G. S.; Allman, S. L.; Chen, C. H.; Kramer, S. D.; Thonnard, Norbert; Willis, R. D. (American Journal of Science, 1986-01-01)
      A new laser-based analytical technique is described for isotope selective noble gas atom counting. The method has been used to detect 81Kr atoms in a groundwater sample.
    • 14C Depth Profiles as Indicators of Trends of Climate and 14C/12C Ratio

      Brown, Robert H. (American Journal of Science, 1986-01-01)
      Composite curvature averages for 14C age depth profiles of deep ocean sediment, continental sediment, and soil each indicate a global trend for 14C age increment per cm depth to increase with 14C age over the range for which a definitive statistical sample is available. The global trend indicated for peat profiles is constant 14C age increment per cm depth over the past 10,000 14C yr. Correlation coefficients between changes in 14C yr/cm and maximum profile thickness contradict compaction as an adequate explanation for the global trend indicated by sediment and soil profiles. This trend must be explained by additional factors such as progressively decreasing contamination from older carbon, increasing cosmic ray intensity, decreasing geomagnetic intensity, diminishing 12C in the active biosphere during profile accumulation, and climate factors affecting the rate of accumulation. The diverse trend of peat profiles may indicate climatic conditions more favorable to peat growth during the earlier portion of the past 10,000 yr.
    • 14C Dating of Calcareous Tufa from Different Environments

      Pazdur, Anna; Pazdur, Mieczysław F. (American Journal of Science, 1986-01-01)
      14C dates of carbonate and organic matter fractions are compared with a series of calcareous tufa samples from selected sites representing different geochemical environments and associated with different bedrocks. Results obtained in this study indicate values of apparent age ranging from 940 +/- 110 yr for calcareous tufas associated with Pleistocene sediments to 2000 +/- 110 yr and even ca 4000 yr for tufas from sites associated with Jurassic or Cretaceous limestone. It was found also that within each of the investigated sites the value of apparent age does not change significantly with the age of the tufa layer.