• Ground-Water Circulation in the Meade Thrust Allochthon Evaluated by Radiocarbon Techniques

      Muller, A. B.; Mayo, A. L. (American Journal of Science, 1983-01-01)
      The Meade thrust, in southeastern Idaho, is a major element of the Western Overthrust Belt. The allochthon is of geo-economic importance both as a potential hydrothermal area and as the principal mining area within the Western Phosphate Field. To assist in the development of these two resources, an understanding of the regional ground-water circulation was sought. Geologic and hydrologic data from boreholes in this area are virtually nonexistent. Waterwell development in the area has not occurred because of the abundance of springs and only a few hydrocarbon exploration boreholes have been drilled. Thus, the problem lends itself to evaluation by isotope hydrologic and geochemical methods. Ten springs from within the thrust block and around its periphery were sampled for major ions, 2H/18O, and 14C/13C analysis. Data from these analyses and from field geologic evidence have identified two distinct flow regimes within the Meade thrust allochthon. Shallow flow systems lie above the impermeable Phosphoria Formation, usually within a few hundred meters of the surface. Most of the spring waters from this system are recent and cool. In all cases, they have mean subsurface residence times of less than a few hundred years. The deeper flow systems which lie below the Phosphoria formation are hydraulically isolated from the shallow system. Warm waters from these springs have 14C contents suggesting mean ground-water residence times on the order of 15,000 years. Although these waters could have circulated to as deep as 1900m, 2H/18O results show that high temperatures were never reached. There is no evidence to suggest that water from beneath the Meade thrust has contributed to the circulation in the allochthon.
    • The Reliability of Archaeologic Interpretation of Radiocarbon Dates

      Willkomm, Horst (American Journal of Science, 1983-01-01)
      14C dates of a medieval settlement with archaeologically well-dated strata are compared with the true ages of the respective layers. The 14C values indicate that each layer may contain older material reaching up to the beginning of settlement. Therefore, the 14C measurement of only a few wood or charcoal samples may lead to age estimations several hundred years too old.
    • High-Precision 14C Measurement of Irish Oaks to Show the Natural 14C Variations from 200 BC to 4000 BC

      Pearson, G. W.; Pilcher, J. R.; Baillie, M. L. (American Journal of Science, 1983-01-01)
      Bi-decade samples of dendrochronologically matched Irish Oak, measured with a precision of ca +/20 years, covering the period 200 to 4000 BC are presented. The data are compared with the published data of Suess, de Jong, and Mook to provide a general calibration of the 14C time scale for this period. Although the dendrochronologic sequences presented are not absolutely tied to present, the best fit (based on 14C evidence) of the Belfast data to absolute chronologies, the error and evidence associated with such positioning is given. The intervals chosen for analysis were 20 years, reducing slightly the resolution of short-term variations when compared to 10-year intervals, which are sometimes measured. However, this calibration would suffice for most scientific purposes and certainly for the calendrical conversion of 14C dates derived from archaeologic samples.
    • The Use of 14C in Natural Materials to Establish the Average Gaseous Dispersion Patterns of Releases from Nuclear Installations

      Otlet, M. L.; Walker, A. J.; Longley, H. (American Journal of Science, 1983-01-01)
      The Harwell Low Level measurements been measuring a variety of natural materials close to United Kingdom nuclear installations measurements are made first, to establish the releases to the atmosphere of 14C as observed tree rings and second, to establish dispersion contours ed over extended periods. The main study area has been Cumbria, around the BNFL nuclear installation at Sellafield. 14C, which can be measured to good precision even at values close to the normal natural levels, provides a powerful technique for the provision of practical experimental values much wanted for theoretical dispersion models.
    • Foreword

      Stuiver, Minze (American Journal of Science, 1983-01-01)
    • Participants

      American Journal of Science, 1983-01-01
    • 14C Dating and Magnetostratigraphy

      Thompson, Roy (American Journal of Science, 1983-01-01)
      The history of the earth's magnetic field is preserved in the fossil magnetism of archaeologic specimens, natural rocks and sediments. Samples such as lava flows and baked sherds that acquired a thermoremanent magnetization on cooling can be used to estimate ancient geomagnetic field intensities and directions. Paleofield directions can also be obtained from fine-grained sediments that acquired detrital magnetic remanence when deposited. Study of the earth's magnetic field over the last few tens of thousands of years yields information on geomagnetic dynamo theories, causes of fluctuations in cosmic-ray activity, and the formulation of a new regional chronologic tool.
    • 13CO2 and 14CO2 Measurements on Soil Atmosphere Sampled in the Western Great Plains of the US

      Haas, Herbert; Fisher, D. W.; Thorstenson, D. C.; Weeks, E. P. (American Journal of Science, 1983-01-01)
      Soil gas samples were obtained from the unsaturated zone at eight sites in the Great Plains. Three of these sites were sampled extensively for gas composition and carbon isotopes. Sampling equipment consisted of a nest of gas probes vertically spaced by roughly 3m at most sites, generally approaching the water table. Water wells, 10cm in diameter, were screened in the topmost layer groundwater. Inverted cattle tanks were used to collect CO2 samples from the soil surface. The major gas components were analyzed with emphasis on CO2, Delta--13C, and 14C measurements. The same components were studied in groundwater samples. Higher than atmospheric CO2 concentrations were found in all soil samples. Root respiration and oxidation of organic matter were sources for the additional CO2. When lignite was present in the unsaturated zone, gaseous oxygen reacted almost completely, and CO2 levels rose to 19%. Near the surface, annual cycles in total CO2, Delta--13C, and 14C were observed. 14C activities were close to present post-bomb levels at the surface and generally declined with depth. At some sites, oxidation of lignite caused decline of 14C levels to 1 or 2% of their surface value at 8m depth. Without lignite, the 14C activity remained above 50% at all depths. Concentrations of total carbon and its isotopes in ground water remained very stable throughout the study. This implies that geochemical processes in the aquifer vary on time scales longer than the seasonal effects observed in the near-surface unsaturated zone.
    • Possibilities in the Dating of Writing Materials and Textiles

      Burleigh, Richard; Baynes-Cope, A. D. (American Journal of Science, 1983-01-01)
    • Possible Depletion in 14C in Trees Growing in Calcareous Soils

      Tauber, Henrik (American Journal of Science, 1983-01-01)
      14C activities of decadal samples from beech trees growing under extreme calcareous conditions were compared to 14C activities of decadal samples of the same age from a beech tree growing in a normal mold soil in order to see whether part of the carbon assimilated during photosynthesis might originate from 14C-deficient carbonates in the soil. The calcareous soils contained from 18 to 52% calcium carbonate, and this carbonate had a mean 14C age of 10,200 to 17,600 years BP. A comparison was also made with the 14C activity of contemporaneous samples from Douglas Fir from the US North Pacific (Stuiver, 1982). No significant depletion in 14C activity in beech trees growing in the highly calcareous soils was detected. The measured mean difference in 14C activity in beech trees from calcareous and non-calcareous sites corresponds to an uptake of 0.12 +/- 0.3% carbon from soil carbonates in the calcareous sites.
    • 14C Variations During the Upper Pleistocene

      Vogel, J. C. (American Journal of Science, 1983-01-01)
      Parallel determinations of 14C and ionium dates on a stalagmite from the Cango Caves provide evidence of variations in the 14C content of the atmosphere beyond the range of the California tree-ring sequence. During the Holocene growth period the 230Th dates are compatible with the tree-ring calibrated 14C dates. At 18,000 BP and between 30,000 and 40,000 BP the 14C ages are markedly younger than the 230Th ages, suggesting that the 14C level of the atmosphere was considerably higher at these times. Between the 230Th ages of 35,000 and 29,000 BP the 14C ages remain nearly constant at 29,500 BP, indicating that 14C production must have been drastically reduced during this period. The 14C fluctuation is greater than that predicted by Barbetti (1980) but it may be explained by postulating a substantial increase in the geomagnetic dipole field, for which there is mounting evidence.
    • Production of C- Directly from CO2 Using the ANIS Sputter Source

      Heinemeier, Jan; Andersen, Hans Henrik (American Journal of Science, 1983-01-01)
      Micro-ampere beams of C- have been produced with the Aarhus negative-ion source, operated on CO2 gas. The efficiency of the source and memory effects have been measured, using 13C-enriched CO2, in order to evaluate the applicability of the source to 14C dating by accelerator mass spectroscopy.
    • Anthropogenic Changes in Organic Carbon and Trace Metal Input to Lake Washington

      Schell, W. R.; Swanson, J. R.; Currie, L. A. (American Journal of Science, 1983-01-01)
      An example of how man's contaminants are introduced, deposited, and retained in sediments giving a chronological record of events has been developed for Lake Washington, Seattle. Significant amounts of both inorganic and organic compounds in the environment originate from fossil fuel sources, such as power plants and motor vehicles. Many organic compounds are introduced also from contemporary biogenic materials. Through the combined carbon isotope analysis technique (CCIA), we can distinguish between fossil and contemporary carbon sources classes (using 14C), as well as sources within each class (using 13C). To establish the chronology of the organic carbon pollutant input to the lake sediment, the ages of the layers were determined using 210pb dating techniques. Sediment profiles of trace metals and a fallout radionuclide plutonium were also obtained and compared with the carbon isotope profiles. The results show that the total organic carbon (TOC) concentration correspond to 93% modern carbon before 1905. This 14C concentration in TOC decreased to ∼60% modern in the 1930's and now is between 95 and 80% modern. The lipid fraction is ca 30% modern and the total aromatic hydrocarbon fraction reached a minimum of 5% modern in 1954. The large decrease in 14C of TOC around 1930 is believed to be due to coal dust or fly ash. The trace metal concentration also increased substantially at this time. The pattern observed in the sediment thus reflects the change in the local energy consumption pattern from a predominately coal to an oil-based economy. From the plutonium profile we infer that mixing occurs for 3 or 4 years before the sediment layers are compacted.
    • Anthropogenic 14C Variations

      Segl, Monika; Levin, Ingeborg; Schoch-Fischer, Hilla; Münnich, Marianne; Kromer, Bernd; Tschiersch, Joche; Münnich, K. O. (American Journal of Science, 1983-01-01)
      Continuous 14C data of 1 or 2 weekly samples of atmospheric CO2 are presented, collected near two nuclear power plants (NPP-Biblis and NPP-Philippsburg) located in the rather densely populated upper Rhine valley. Tree-leaf and tree-ring samples from the area of a boiling water reactor in northern Germany (NPP-Würgassen) are also presented and discussed. Additional atmospheric 14CO2 samples from two continental ‘clean-air’ stations in Germany and Austria were used as reference for the polluted areas. For January 1982, these samples yield a ‘clean-air’ 14C concentration in central Europe of Delta-14C=255 +/- 5 per mil (7.7pCi/gC = 1.45pCi/m3 air). In the vicinity of boiling water reacctors we found a mean excess in Delta-14C activity of ca 53 per mil (0.05pCi/m3 air) above the local level during normal periods of reactor operation. During revision, however, the Delta-14C excess may reach up to 300 per mil above the local background. From this, we calculate source strengths of ca 20Ci/GWa on the average, with peak values of up to 2Ci/week during specific periods. Pressurized water reactors emit 14C mainly as hydrocarbons, and consequently, we found no additional 14CO2 near the Biblis reactor. Stations located in the Rhine valley show significant summer-winter 14CO2 variation due to intensive fossil-fuel combustion. The fossil-fuel admixture leads to a depression of the 14C level and reaches Delta-14Cdepr = 120 per mil in winter; summer values, however, are only slightly lower than the 'clean-air' level.
    • Radioisotope Dating with the ETHZ-EN-Tandem Accelerator

      Wölfli, Willy; Bonani, Georges; Suter, Martin; Balzer, Richard; Nessi, Marzio; Stoller, Christian; Beer, Jürg; Oeschger, Hans; Andrée, Michael (American Journal of Science, 1983-01-01)
    • A Secondary Standard for Radiocarbon Dating

      Angiolini, Fernando E.; Albero, Miguel C. (American Journal of Science, 1983-01-01)
      The preparation and calibration of a secondary standard for the INGEIS Radiocarbon Dating Laboratory are presented. This standard is barium carbonate with a specific activity almost twice that of NBS oxalic acid. It was prepared from BaCO3 with high specific activity and commercial potassium carbonate by an isotopic dilution technique. The advantages of this standard are: 1) the preparation is simple and can be achieved with ordinary labware; 2) the production of CO2 by acid attack from this carbonate shows minimum isotopic fractionation. At least, it has less fractionation than wet oxidation of oxalic acid, the problems of which are described in the literature. This standard ensures better reproducibility in activity measurements; 3) despite some problems of activity exchange with atmospheric CO2 concerning carbonates, measurements of activity over a period of about two years have shown no significant deviation from the mean value. A tentative explanation of this phenomenon is also given. The activity ratio between BaCO3 and NBS oxalic acid is given with its error, and the statistical tests used in the calibration are briefly explained. Finally, a control chart for the activity of the standard over a long period is drawn, showing non-significant deviation and supporting the usefulness of this standard.
    • Accelerator Mass Spectrometry: From Nuclear Physics to Dating

      Kutschera, Walter (American Journal of Science, 1983-01-01)
    • Radiocarbon Dating of Tufa in Paleoclimatic Studies

      Srdoč, Dušan; Horvatinčić, Nada; Obelić, Bogomil; Sliepčević, Adela (American Journal of Science, 1983-01-01)
      Calcareous deposits known as tufa or travertine contain biogenic carbon and are a potential source of geochronologic information. Many dated samples from Karstic regions in Yugoslavia proved that 14C analyses of tufa can provide reliable data reflecting climatic conditions in the past. Systematic dating of tufa samples revealed two distinct groups of deposits: recent tufa deposits, with a sharp age limit of ∼6000 +/- 500 years BP, and old tufa deposits with 14C age ranges from 25,000 +/- 2300 years BP to the lowest limit of our 14C dating system (∼37,000 years). A histogram based on the initial activity AO = 0.85 shows the age distribution of randomly sampled tufas vs sample frequency. A time gap between ∼6000 BP and ∼23,000 BP is evident, reflecting cooler climatic conditions. The start of peat deposition is coincident with that of tufa growth in the Holocene. Paleoclimatic implications of tufa growth periods obtained by 14C dating are as follows: climatic conditions that favor tufa formation at least in karstic regions, are very stringent. Therefore, climatic conditions, such as mean annual temperature and humidity, as well as hydrologic and vegetational conditions, must have been very similar in periods of tufa growth. While recent tufa deposits are coincident with the warm Holocene period, old tufa can be associated with warm interstadials in the Würm.
    • Atmospheric Radiocarbon: Implications for the Geomagnetic Dipole Moment

      Sternberg, R. S.; Damon, P. E. (American Journal of Science, 1983-01-01)
    • Long-Term Variability of Temperature and 14C in the Gulf Stream: Oceanographic Implications

      Druffel, Ellen M. (American Journal of Science, 1983-01-01)
      Variability in temperature and 14C levels are recorded in coralline aragonite that grew in the Gulf Stream during the past four centuries. In particular, 18O/16O ratios reflect a decrease of ca 1 degree C in surface water temperature during the latter part of the Little Ice age. 14C levels also rose in the surface waters of the Gulf Stream and in atmospheric CO2 during the Maunder minimum. These observations indicate that ocean circulation may have been significantly different in the North Atlantic around the beginning of the 18th century.