• 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).
    • Precise Calendrical Dating of Known Growth-Period Samples Using a 'Curve Fitting' Technique

      Pearson, G. W. (American Journal of Science, 1986-01-01)
      Absolute high-precision radiocarbon time-scale calibration is now available and is shown by Stuiver and Pearson (1986) and Pearson and Stuiver (1986) to be internationally valid. The technique of curve fitting presented in this paper shows how certain samples may be dated calendrically to within a very narrow band width ca +/- 20 years, at time periods when single sample analysis would give ambiguous calendrical conversion. Samples of known deposition rate covering a time span of >50 years are subdivided to produce a 'floating curve' and this curve is then `wiggle matched' with the high-precision calibration to give a precise calendrical age.
    • 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.
    • Palaeosols Within Loess: Dating Palaeoclimatic Events in Kashmir

      Kusumgar, Sheela; Agrawal, D. P.; Juyal, Navin; Sharma, Prabhakar (American Journal of Science, 1986-01-01)
      The 14C dates of Kashmir loess-palaeosols form five clusters. The dates, mineral magnetic, stable isotopic, and pollen data help decipher major climatic oscillations as distinct from the minor ones.
    • Progress at the IsoTrace Radiocarbon Facility

      Beukens, Roelf P.; Gurfinkel, Debbie M.; Lee, Henry W. (American Journal of Science, 1986-01-01)
      Since August 1984 over 100 samples have been analyzed. 12C, 13C, and 14C isotopes were measured after acceleration and all dates were corrected for natural and preparation-induced fractionation. A precision of better than 1.0% was obtained for samples 10,000 yr BP or less and these results were shown to be reproducible at precision levels as low as 0.3%. An accuracy of better than 1.0% was demonstrated for the same age range by analyzing samples which were previously dated with the conventional technique. The machine background, measured on blank sample holders in a clean ion source, yielded a count rate equivalent of 0.015 +/- 0.007% modern.
    • Use of AMS 14C Analysis in the Study of Problems in Aspartic Acid Racemization-Deduced Age Estimates on Bone

      Ennis, Paul; Noltmann, E. A.; Hare, P. E.; Slota, P.; Payen, L. A.; Prior, C. A.; Taylor, R. E. (American Journal of Science, 1986-01-01)
      Major discordances between AMS 14C- and aspartic acid racemization (AAR)deduced age estimates on bone samples have led to an examination of factors other than time and temperature that can fundamentally influence the degree of racemization observed in fossil bone. Our studies support previous suggestions that for many bone samples the chemical state of amino acids must be routinely considered if AAR-deduced age estimates are to be used to make meaningful chronologic inferences.
    • 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.
    • 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.
    • 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.
    • Radiocarbon Dating with the University of Washington Accelerator Mass Spectrometry System

      Grootes, Pieter M.; Stuiver, Minze; Farwell, George W.; Leach, Donald D.; Schmidt, Fred H. (American Journal of Science, 1986-01-01)
      The University of Washington FN tandem accelerator mass spectrometry (AMS) system has been used in a series of 14C studies. 1) The 14C concentrations in annual growth rings for 1962, 1963, and 1964 of a Sitka spruce, each divided into ten sequential segments, were measured; a full and rapid response of tree-ring cellulose to atmospheric changes in 14CO2 is indicated, with a delay, if any, of not more than three weeks. 2) The 14C concentrations in two chemical fractions of dissolved organic carbon and in two fractions (by size) of particulate organic carbon were measured for Amazon River samples from several locations. All contain bomb carbon, but the amounts differ significantly. 3) Algae samples from lakes in the dry valleys of Antarctica were dated in order to assist in the reconstruction of the climatic history of Antarctica. 4) Background studies indicate that the contribution of the AMS system itself to the observed 14C concentrations is equivalent to an age of ca 60,000 14C yr BP; for a prepared sample of 5mg of carbon the background corresponds to ca 50,000 years.
    • Archaeologic Sherd Dating: Comparison of Thermoluminescence Dates with Radiocarbon Dates by Beta Counting and Accelerator Techniques

      Johnson, R. A.; Stipp, J. J.; Tamers, M. A.; Bonani, Georges; Suter, Martin; Wölfli, Willy (American Journal of Science, 1986-01-01)
      Sherds can be dated by four independent methods. 14C beta counting on associated material, accelerator mass spectrometry on carbon traces on and within the sherd, thermoluminescence studies on minerals within the sherd, and stylistic form. Age analyses of materials and sherds from several sites are shown in this work. Each technique has its own frequently encountered non-laboratory sources of error. A combination of at least two independent techniques is indispensable for the highest level of confidence.
    • Background Measurements with Different Shielding and Anticoincidence Systems

      Loosli, H. H.; Forster, Markus; Otlet, R. L. (American Journal of Science, 1986-01-01)
      Extremely low background count rates are a necessary condition for both the measurement of 39Ar concentrations in ground and ocean water and of 14C activities in small samples using gas proportional counting techniques. A systematic comparison of the performance of three different designs of shielding systems in four different installations has been made. Background values of selected gas proportional counters were measured, compared and separated into their various components. Acceptably low backgrounds were obtained in all the systems tried. The performance of a Nail shield in a surface laboratory was found to be at least equal to the best obtained with a gas ariticoincidence detector in a deep underground laboratory.
    • Measurement of 14C Directly from CO2 Using a Tandetron Accelerator Mass Spectrometer Facility

      Raisbeck, Grant M.; Yiou, Françoise; Arnold, Maurice; Duplessy, Jean Claude (American Journal of Science, 1986-01-01)
      Tests have been carried out on the measurement of 14C directly from CO2, using a source designed by Middleton, and a Tandetron accelerator mass spectrometer system. These tests were very promising from the point of view of minimum quantity of carbon necessary (<50 micrograms), but suffered from a background (apparently not memory effect) giving an equivalent age of 25,000 years. As a demonstration of the technique, a single thread from the mummy wrapping of the Egyptian king Ramses II was dated.
    • Bomb Produced 14C Content in Tree Rings Grown at Different Latitudes

      Dai, Kai-Mei; Fan, C. Y. (American Journal of Science, 1986-01-01)
      The 14C content in 1961-1967 rings of each of three spruce pines grown at (68 degrees N, 130 degrees W), (47 degrees 30' N, 129 degrees 16' E) and (27 degrees 13' N,100 degrees 20' E) were measured. Delta-14C values of the three specimens rise dramatically from a common level (~250 per mil) in 1961 to their respective maxima, 964 per mil, 909 per mil, and 743 per mil in 1964 and then fall to a common level ~680 per mil in 1967. The observed Delta-14C increase comes most likely from the nuclear bomb test of the USSR at 75 degrees N in 1961, although there were many other tests since the 1950s. The different effects at different latitudes reflect the atmospheric circulation patterns in the stratosphere and the transport of 14C nuclei from the stratosphere to the troposphere.
    • Foreword

      Stuiver, Minze (American Journal of Science, 1986-01-01)
    • Secular Variations of Cosmogenic 14C on Earth: Their Discovery and Interpretation

      Suess, Hans E. (American Journal of Science, 1986-01-01)
      Measurement of 14C in samples of wood of precisely known age have shown that the cosmogenic 14C content of the CO2 in the atmosphere has not remained constant during the period of time covered by radiocarbon dating. As the terrestrial atmosphere mixes with a time constant of less than 3 years, these variations must be essentially independent of geographic location. The 14C in atmospheric CO2 must be a quantity that, at a given time, pertains to the terrestrial atmosphere as a whole. Not only is its knowledge necessary for deriving accurate radiocarbon dates, but it is also valuable in connection with many geophysical and astrophysical problems. Unfortunately, progress in our knowledge of 14C variations in the terrestrial atmosphere has been delayed by hidden experimental errors in results obtained by many laboratories. By rigorous statistical analysis of the La Jolla results, it is now possible to show that the 14C variations are not simple random fluctuations but show distinct regularities. Similar patterns of variations have been found in the growth rate of trees during the last 5000 years. Measurements of radiogenic 10Be currently being done by European workers promise to conclusively elucidate the 14C findings.
    • 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.
    • Thin Layer delta-13C and Delta-14C Monitoring of "Lessive" Soil Profiles

      Becker-Heidmann, Peter; Scharpenseel, Hans-Wilhelm (American Journal of Science, 1986-01-01)
      The natural 14C and 13C content of soil organic matter and their dependence on depth for two Alfisols are presented. This soil type which covers a large area of the earth's surface is characterized by clay migration processes ("Lessivé"). The samples were taken as successive horizontal layers of 2cm depth from an area of ca 1 m2 size as deep as the C content allows 14C analysis. The minima of the D14C distribution decrease with depth, while the maxima increase in the upper, leached horizon (A1) due to bomb 14C and decrease in the lower, clay illuviated (Bt). delta-13C indicates proceeding decomposition in Al and protection of carbon, probably due to the formation of clay humus complexes in Bt. delta-13C values were also used for age correction of the 14C data due to isotopic fractionation. The D14C and delta-3C depth distributions are characterized by sharp peaks at the boundaries of the horizons, probably caused by the influence of textural changes on the transport of C with percolating water.