• 13C Variation in Limestone on an Aquifer-Wide Scale and Its Effects on Groundwater 14C Dating Models

      Muller, A. B.; Mayo, A. L. (American Journal of Science, 1986-01-01)
      In modeling the initial 14C activity of ground waters, the delta-13C of marine limestone is taken conventionally to vary little about 0 per mil PDB. This variation was found to be 6.28 per mil in samples taken over intervals from 10^-2 to 1^5 meters in the Mooney Falls Member of the Redwall Limestone in northern Arizona. Such a variation will cause appreciable variability in the results of all four initial activity models tested. The variability, due primarily to a numerical instability in the models dependent on this parameter, can introduce significant uncertainty into groundwater "age" calculations.
    • 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.
    • 14C Dating of Plant Macrofossils in Lake Sediment

      Andree, Michael; Oeschger, Hans; Siegenthaler, Ulrich; Riesen, Trudi; Moell, Markus; Ammann, Brigitta; Tobolski, Kazimierz (American Journal of Science, 1986-01-01)
      Macrofossils of terrestrial plants have been picked from a sediment core taken in Lake Lobsigen, a small lake on the Western Swiss Plateau. The sediments were previously analyzed for pollen composition, plant and animal macrofossils, and stable isotopes. Plant macrofossils were selected near pollen zone boundaries in Late Glacial and early Postglacial sediment for 14C dating by AMS. In the same lake carbonate and gyttja (aquatic plant) samples were dated by decay counting. The dates on terrestrial material are generally younger than those on carbonate and gyttja, ie, material reflecting the 14C/C ratio of dissolved bicarbonate in lake water. This is probably due to a contribution of dissolved limestone carbonate and thus a somewhat reduced 14C/C, ratio in the lake's water (hard water effect).
    • 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 in the Deep Water of the East Atlantic

      Schlitzer, Reiner (American Journal of Science, 1986-01-01)
      The renewal of east Atlantic deep water and its large-scale circulation and mixing have been studied in observed distributions of temperature, silicate, Sigma-CO2, and 14C. 14C variations in northeast Atlantic deep water below 3500m depth are small. Delta-14C values range from -100 per mil to -125 per mil.14C bottom water concentrations decrease from &4C = -117 per mil in the Sierra Leone Basin to Delta-14C = -123 per mil in the Iberian Basin and are consistent with a mean northward bottom water flow. The characteristic of the water that flows from the west Atlantic through the Romanche Trench into the east Atlantic was determined by inspection of theta/Delta-14C and theta/Si02 diagrams. A mean potential temperature of theta = 1.50 +/- .05 degrees C was found for the inflowing water. A multi-box model including circulation, mixing, and chemical source terms in the deep water has been formulated. Linear programing and least-squares techniques have been used to obtain the transport and source parameters of the model from the observed tracer fields. Model calculations reveal an inflow through the Romanche Trench from the west Atlantic, which predominates over any other inflow, of (5 +/- 2) Sv (potential temperature 1.50 degrees C), a convective turnover of (150 +/- 50) years and a vertical apparent diffusivity of (4 +/- 1) cm2/s. Chemical source terms are in the expected ranges.
    • A 14C Electronic Measurement System with a Microcomputer

      Walanus, Adam (American Journal of Science, 1986-01-01)
      Even though the reliability of equipment has improved, the quality of measurement should still be checked. This task may be performed by a microcomputer with the physicist's intervention only when an error in measurement is detected.
    • A Computer Program for Radiocarbon Age Calibration

      Stuiver, Minze; Reimer, P. J. (American Journal of Science, 1986-01-01)
    • A Discussion of an Alternate Approach to the Evaluation of Sample Contamination

      Gurfinkel, D. M. (American Journal of Science, 1986-01-01)
      An approach to the evaluation of sample contamination based on the monitoring of contaminant removal during pretreatment is described. Spot tests and colorimetric reactions which could be adapted for this purpose are suggested.
    • A Low-Cost Miniature Counter System for Radiocarbon Dating

      Jelen, Kazimierz; Geyh, Mebus A. (American Journal of Science, 1986-01-01)
      Despite the great potential of the AMS technique for 14C dating of milligram samples, the use of multiple miniature counter systenis is still promising. Investment costs are relatively low and long-term financing of age determinations can be held within bounds. We have developed a 14C dating systeni containing 10 miniature counters for $30,000, whereas commercial systems usually cost more than $150,000. Counting is not quite as good as that of the technically more sophisticated commercial systems, but the disadvantage for routine work is not significant. CO2 preparation and purification take less than 30 minutes of active work including measurement and data evaluation. The cost of one age determination on a 22mg sample is about $35.00.
    • A Review of the Operation of the Oxford Radiocarbon Accelerator Unit

      Batten, R. J.; Bronk, C. R.; Gillespie, Richard; Gowlett, J. A. J.; Hedges, R. E. M.; Perry, Colin (American Journal of Science, 1986-01-01)
      We describe here the general operation of the Oxford Radiocarbon Accelerator Laboratory which has now been dating routinely for 18 months.
    • A Study of Errors in 14C Dates of Peat and Sediment

      Olsson, Ingrid U. (American Journal of Science, 1986-01-01)
      It is a well-established fact that 14C dates from lake sediments are usually too old because of contamination with allochthonous material and/or due to discrete reservoir effects. The latter can occur in soft water lakes and may be examined by the 14C measurement of aqueous plants or the carbon dissolved and suspended in the water column. Some plants assimilate CO2 from the sediment. Their 14C activity is then dependent on the sediment accumulation rate and nutrients stored in the root system may also contribute misleading results. If water is filtered through ultra-fine membranes and then treated chemically, several fractions can be isolated for dating. The present study shows that the 14C activity of such fractions varies widely but with the weighted mean indicating an overall deficiency. Even the water from a raised bog evidences a 14C deficiency relative to contemporary atmospheric CO2. Charcoal from an archaeologic site and peat from corresponding layers in a nearby bog have yielded significantly different ages. The fact that the Cladium peat was from a very calcareous area is significant. The risk of contamination by younger root material is also documented.
    • Accelerator Mass Spectrometry with Fully Stripped 36Cl Ions

      Haberstock, Günther; Heinzl, Johann; Korschinek, Gunther; Morinaga, Haruhiko; Nolte, Eckehart; Ratzinger, Ulrich; Kato, Kazuo; Wolf, Manfred (American Journal of Science, 1986-01-01)
      A description of accelerator mass spectrometry (AMS) measurements with the long-lived radioisotope 36Cl is given. All measurements were made at the Munich tandem accelerator laboratory. Results are presented for 36Cl measurements in ground waters, in the meteorite Bjurböle, in ice-core samples of the Vernagtferner, Austria, and in granite samples from Hiroshima, Japan, irradiated by the atomic bomb explosion in 1945.
    • Accelerator Radiocarbon Dating at SFU

      Nelson, D. E.; Vogel, J. S.; Southon, J. R.; Brown, T. A. (American Journal of Science, 1986-01-01)
      The Simon Fraser University accelerator mass spectrometry (AMS) facility has now been in semi-routine use since the beginning of 1985. The advantages and limitations for 14C dating are described.
    • AMS Radiocarbon Dates on Foraminifera from Deep Sea Sediments

      Andree, Michael; Oeschger, Hans; Broecker, Wallace S.; Beavan, Nancy; Mix, Alan C.; Bonani, Georges; Hofmann, Hans Jakob; Morenzoni, Elvezio; Nessi, Marzio; Suter, Martin; et al. (American Journal of Science, 1986-01-01)
      14C ages were determined on samples of foraminifera separated from cores from three areas of the tropical Pacific (Fast Pacific Rise, Oontong Java Plateau, and South China Sea). Analyses were made on four planktonic species and on mixed benthics. The purpose of the multiple analysis on planktonic species is to assess the importance of artifacts resulting from the bioturbation-abundance change couple, from the bioturbation-partial dissolution couple and from redeposition by bottom currents. The goal is to use the benthic-planktonic age difference as a means of establishing changes in deep sea ventilation rate over the past 25,000 years. Results of a part of this work are presented in this paper.
    • An Intercomparison of Some AMS and Small Gas Counter Laboratories

      Burleigh, Richard; Leese, Morven; Tite, Michael (American Journal of Science, 1986-01-01)
      The performance of six laboratories with the capacity to date small samples (4 AMS and 2 small gas-counter laboratories) has been compared using 100mg samples of textiles from Ancient Egypt and Peru, with the British Museum laboratory acting as independent coordinator. This intercomparison was one of normal practices and has demonstrated that a coherent series of results can be obtained when several laboratories undertake blindfold measurements, although the occurrence of outliers emphasizes the continuing need for the dating of unusually important or controversial samples to be undertaken by a group of laboratories.
    • Announcement of a New Collaborative Study for Intercalibration of 14C Dating Laboratories

      Scott, E. M.; Baxter, M. S.; Aitchison, T. C.; Harkness, D. D.; Cook, G. T. (American Journal of Science, 1986-01-01)
      A proposal for an international collaborative study to investigate and assess the existence of inter-laboratory variability is discussed. The proposed study would be conducted over two years and would investigate each stage of the dating process in turn.
    • Annual Variations of the 14C Content of Soil CO2

      Dörr, Helmut; Münnich, K. O. (American Journal of Science, 1986-01-01)
      A 6-year and a 2-year record of 14C measurements of soil CO2 in two soils are presented and discussed. The annual 14C variation of soil CO2 is controlled by the seasonally varying contribution of root respiration and of microbial decomposition of organic matter producing soil CO2. The Delta-14C soil CO2 difference between summer and winter is ca 50 per mil in a soil where turnover of organic matter is fast (r = 2.5a) and ca 100 per mil in a soil of slow turnover (r = 60a). A simple model describing the movement and turnover of organic matter is derived, giving the depth distributions of organic carbon and of 14C. The model needs a subdivision of the carbon reservoir into at least two reservoirs with residence times of r1= 1a and r2 = 100a, respectively, and with a vertical transfer velocity in the order of 0.6mm/a.
    • Anomalous High 14C Activity Found in Recent Corals from the Philippines

      Willkomm, Horst (American Journal of Science, 1986-01-01)
      The carbonate skeletons of small living corals collected in Spring 1981 from Cebu Island, the Philippines, had 14C activities up to 147% of recent standard. Similarly high values were found in the carbonate structure of three large coral heads, where the 14C content of six penetrating cores was measured. In these corals the activity of the outer parts grown since 1960 reached values as high as 155% (corrected for delta-13C = -25 per mil) while the inner part grown from 1860 to 1950 had values of 106 to 110%. The 14C content of corals should be ca 116% due to the atomic bomb effect and 95% before 1955. The samples were taken from the shore, exposed to tidal waters, so that local contamination is improbable. Organic samples collected from the same region showed normal 14C activity.
    • Anthropogenic Radiocarbon: Past, Present, and Future

      Povinec, Pavel; Chudý, Martin; Šivo, Alexander (American Journal of Science, 1986-01-01)
      14C is one of the most important anthropogenic radionuclides released to the environment by human activities. Weapon testing raised the 14C concentration in the atmosphere and biosphere to +100% above the natural level. This excess of atmospheric 14C at present decreases with a half-life of ca 7 years. Recently, a new source of artificially produced 14C in nuclear reactors has become important. Since 1967, the Bratislava 14C laboratory has been measuring 14C in atmospheric 14CO2 and in a variety of biospheric samples in densely populated areas and in areas close to nuclear power plants. We have been able to identify a heavy-water reactor and the pressurized water reactors as sources of anthropogenic 14C. 14C concentrations show typical seasonal variations. These data are supported by measurements of 3H and 85Kr in the same locations. Results of calculations of future levels of anthropogenic 14C in the environment due to increasing nuclear reactor installations are presented.
    • Applications of the Use of Hawthorn Berries in Monitoring 14C Emissions from a UK Nuclear Establishment Over an Extended Period

      Walker, A. J.; Otlet, R. L.; Longley, Harry (American Journal of Science, 1986-01-01)
      The paper describes a study undertaken to examine the dispersion pattern of gaseous emissions, as indicated by 14C uptake in natural materials, around the nuclear reprocessing plant at Sellafield, Cumbria, UK. The extent and directional dispersion of the released 14C is established and its variability over an extended period assessed. Results of measurements taken during three sampling seasons (1981,1982,1983) of the 14C activity in hawthorn berries collected over a wide area are presented and the dispersion pattern contours constructed from them are examined. Only limited agreement of the results with the theoretical relationship 1/r is found and both meteorology and topography are seen to be important in determining the shape of the observed patterns.