• New Measurements of the 81Kr Atmospheric Abundance

      Kuzminov, V. V.; Pomansky, A. A. (American Journal of Science, 1980-01-01)
      We have determined the 81Kr activity to be (0.067 +/- 0.003) decay/min. 1 krypton. Using this activity in conjunction with our new measurement of the 80 KR(n,y)81Kr reaction cross-section of (12 +/- 4)b, we infer that the 81Kr activity is 1.5-2.0 times that which would be calculated calculated using the current cosmic ray flux. This implies that the average cosmic ray intensity in the atmosphere during the 81Kr life-time was greater than the current intensity, a fact that has implications for the 14C time scale.
    • Natural Radiocarbon Variations from AD 200 to 800

      Bruns, Michael; Münnich, K. O.; Becker, Bernd (American Journal of Science, 1980-01-01)
      High precision radiocarbon measurements (+/- 2.5 per mil STD) were carried out on absolutely dated European oak material. These showed that significant shortterm atmospheric 14C variations of up to 2 percent occurred between AD 200 and 800. These changes, reflecting a 150-to 180-year periodicity, seem to correlate with the average sunspot activity around that time. In comparison with results obtained by other authors, a very regular pattern of natural atmospheric 14C variations is exhibited.
    • Regional Sources of Volcanic Carbon Dioxide and Their Influence on 14C Content of Present-Day Plant Material

      Bruns, Michael; Levin, Ingeborg; Münnich, K. O.; Hubberten, H. H.; Fillipakis, S. (American Journal of Science, 1980-01-01)
      14C measurements were made on present-day plant material with short integration times (tree leaves and sprouts) in the Eifel area, western Germany, where ancient volcanism produces gaseous emanations of considerable yield. Plants growing near sources emanating 14C-free CO2 show a significant depletion in the period of their growth. The same effect is found in the 14C content of recent samples from the Thera (Santorini) Archipelago/Greece. This mixing of "dead" CO2 may lead to pseudo ages in archaeologic or geologic samples of up to 1600 years in samples from the vicinity of CO2 emanating sources.
    • Computer-Matched Radiocarbon Dates of Floating Tree-Ring Series

      Kruse, H. H.; Linick, T. W.; Suess, H. E.; Becker, Bernd (American Journal of Science, 1980-01-01)
      The absolute time of growth of a floating tree-ring series is determined by computer, by first fitting a curve to the 14C ages of tree-ring dated wood and then by matching the 14C ages of the floating tree-ring series to that curve. The results obtained by this matching procedure are given here for five floating European oak chronologies for which 14C dates have been published previously by Suess (1978). Three of these five floating series have been linked together dendrochronologically. There now remain three floating series covering a 4000-year time span from 4820 BC to 830 BC. Their 14C dates, matched by computer to the bristlecone pine chronology, provide a possibility of obtaining precise ages of oak wood series from Neolithic sites in Switzerland and South Germany by dendrochronologically cross-dating with the calibrated master chronologies.
    • Conditions Involved in Dating Terrestrial Shells

      Evin, Jacques; Marechal, Joelle; Pachiaudi, Christiane; Puissegur, J. J. (American Journal of Science, 1980-01-01)
      Mollusks living only on ground surface can be expected to give the most reliable results in 14C dating from carbonates of continental origin. One may assume they have a homogeneous biotope and are not affected by any hard-water effect. In order to verify these assumptions and to test shells as routine dating material, results from terrestrial gastropods are compared with other 14C dates from classic biologic material, such as peat, charcoal, or bone, collected in the same archaeologic or geologic levels in miscellaneous places. Two sites were selected for which other chronologic data, such as prehistoric industries or malacologic diagrams were available. All results indicate older values for 14C shell dates. The discrepancy between "normal" and snail dates amounts to 300 to 1200 14C years and remains the same whatever the absolute age of the sample. All 13C values of perfectly cleaned shells are between -5 to -10 per mil versus PDB. The initial 14C content of shells that is too low may be different according to species, as suggested by 13C variations. Although fairly constant, this deviation of 14C ages generally makes such samples unreliable for most archaeologic studies, which often need more precise results. However, some measurements were performed on microfauna shells from several Wurmian loess to show that dating of shells may be useful in fairly ancient geologic sediments for lack of better carbonaceous samples. Good agreement of some snail dates with expected sediment ages point to the importance of proper sample selection and pretreatment that might be checked by 13C measurements.
    • Low-Level Liquid Scintillation Counting in an Underground Laboratory

      Schotterer, Ulrich; Oeschger, Hans (American Journal of Science, 1980-01-01)
      A commercial liquid scintillation counter (LSC) was tested for its ability of low level counting (LLC) in two underground laboratories (70m of water equivalent cover). Reduction of total background and background components compared to the normal counting laboratory (5m we. cover) up to a factor of 9 depending on the energy range and the shielding of counting cell and laboratory walls were obtained. First experiments with a large volume cell (50cc) led to a modern 14C net effect of 425cpm and a corresponding background of 1.6cpm.
    • Medium-Term Atmospheric 14C Variations

      De Jong, A. F. M.; Mook, W. G. (American Journal of Science, 1980-01-01)
      High-precision 14C measurements are presented, carried out on single tree rings from a section of the floating South German Neolithic tree-ring chronology. They confirm the existence of pronounced medium-term variations in the order of 2 percent during the 33rd to 38th centuries BC. These variations turn out to be very regular while the precision of 1.5 per mil allows a comparison with a geochemical model calculation. Good agreement is acquired for an input function with a periodicity of about 150 years and an amplitude of approximately 30 percent in the 14C production rate.
    • Foreword

      Stuiver, Minze (American Journal of Science, 1980-01-01)
    • Mini-Radiocarbon Measurements Chemical Selectivity, and the Impact of Man on Environmental Pollution and Climate

      Currie, Lloyd A.; Klouda, George A.; Cooper, John A. (American Journal of Science, 1980-01-01)
      Underlying principles and results are presented for our program to use isotopic and chemical methods to quantify anthropogenic and natural sources of carbonaceous pollutants. Radiocarbon data have been obtained with a specially. developed miniature low-level gas counting system which has permitted us to assay samples containing as little as 5mg carbon. Measurements of carbonaceous particles, using chemical selectivity and size fractionation to supplement the radiocarbon data, have revealed major impact from both fossil fuel and vegetative (contemporary) sources on urban aerosols. Residential wood-burning has been specifically identified as an important source of respirable particles. Current investigations are directed toward the carbonaceous gases and the application of the accelerator technique for the assay of radiocarbon in individual chemical fractions containing microgram quantities of carbon.
    • Isotopic Fractionation of NBS Oxalic 14C Standard and Its Effect on Calculated Age of Materials

      Nehmi, Victor A. (American Journal of Science, 1980-01-01)
      There is much controversy about the significance to radiocarbon dating of isotopic fractionation during the oxidation to CO2 of NBS oxalic acid, the carbon-14 dating standard. To check the effect of fractionation, 30 routine potassium permanganate oxidations of oxalic acid were performed. The isotopic composition of resulting CO2 was determined mass-spectrometrically. delta-13C results ranged between -17.7 and -21.2, with an average of -18.9 per mil wrt PDB. The effect of not applying an isotopic fractionation correction to NBS oxalic acid when performing age calculations is evaluated.
    • On the Climate-Radiocarbon Relationship: Nitric Oxide and Ozone as Connecting Links Between Radiation and the Earth's Surface Temperatures

      Roedel, Walter (American Journal of Science, 1980-01-01)
      The correlations between atmospheric radiocarbon cencentrations, on the one hand, and solar activity and the earth's magnetic field, on the other, as well as possible relations between surface temperatures and solar activity and the earth's magnetic field are considered. To draw a consistent picture of these relations, the following mechanisms for climatic changes are proposed: The earth's magnetic field and solar activity both influence the fluxes of charged solar particles into the upper stratosphere; higher surface temperatures are positively correlated with higher particles fluxes. Charged particles produce nitric oxide, which controls, to some extent, the ozone destruction and, thus, the ozone inventory in the upper layers of the stratosphere (above the 10 mbar level) in latitudes greater than about 60 degrees. The varying ozone contents in the upper stratosphere affect the radiation balance and the temperatures on the earth's surface. It has been estimated that a reduction, or increase, respectively, of ozone in the layers above 10 mbar warms, or cools, respectively, the earth's surface. A change of ozone in the lower layers of the stratosphere has the opposite effect. The maximum net effect is in the order of Delta-T is approximately equal to 0.3 1 K, in both directions. This hypothesis might be in accordance with an orbital origin of long-term climatic changes.
    • Geomagnetic Strength Over the Last 50,000 Years and Changes in Atmospheric 14C Concentration: Emerging Trends

      Barbetti, Mike (American Journal of Science, 1980-01-01)
      Palaeomagnetic field strength measurements for the last 50,000 years are summarized. The period before 12,000 yr bp** is characterized by low dipole moments, but high values are associated with the Lake Mungo polarity excursion between ~32,000 and 28,000 yr bp. The variation since 12,000 yr bp, based on new results from Australia and published data from the Northern Hemisphere has a quasi-cyclic appearance with maxima at ~10,000 and ~3500 yr bp. The geomagnetic record is used to predict variations in atmospheric 14C concentration, and the results are compared with independent comparisons between 14C and other dating methods. Long-term variations in the 14C time-scale are readily explained by known geomagnetic changes.
    • The Concept of DC Gain in Modeling Secular Variations in Atmospheric 14C

      Lazear, Gregory; Damon, Paul E.; Sternberg, Robert (American Journal of Science, 1980-01-01)
      A constraint on radiocarbon reservoir models is that the DC gain of a system (system transfer function at zero frequency) should equal the equilibrium ratio of the atmospheric radiocarbon mass to the production rate. The simple one-box model is essentially a "black box" but the value of the single residence time is theoretically equal to the DC gain. Using a sunspot-production rate algorithm as the forcing function, predictions of the one-box model match the 14C data from AD 1700 to 1900 better than the 3-box, 5-box and box-diffusion models. The more complex models tend to pile up 14C in the atmosphere because their DC gains are too high, and they overattenuate the de Vries "wiggles". The DC gains can be reduced to more acceptable levels by adjusting model parameters, particularly the sizes of the ocean reservoirs. Better fits to the "wiggles" are also obtained by parameter adjustment. Water content of deep-sea sediments constitutes an extra reservoir for dead carbon, and should help reduce system DC gain.
    • The Effect of Anthropogenic CO2 and 14C Sources on the Distribution of 14C in the Atmosphere

      Levin, Ingeborg; Münnich, K. O.; Weiss, Wolfgang (American Journal of Science, 1980-01-01)
      14C measurements on continuous weekly samples of atmospheric CO2 and hydrocarbons, collected in a rather densely populated area are presented. The deviation of the measured 14C data from the clean air level is primarily due to CO2 from the combustion of fossil fuels. This is confirmed by fossil fuel admixture estimates individually calculated with an atmospheric dispersion model. Up to 10 percent admixture is predicted by this model and observed from the 14C shift for weekly averages, particularly during the winter season. Natural CO2 admixture due to soil respiration, however, even in winter, is of the same order of magnitude, but much larger in the warm season: the considerable variations in CO2 concentration in summer are almost exclusively controlled by natural sources. Using tree leaf samples, we have been able to identify boiling water reactors (BWR) as weak sources of 14CO2. Atmospheric samples taken in the environment of the pressurized water reactors (PWR) Biblis show that the 14C release of these reactors is primarily in the form of hydrocarbon 14C. The source strength of the various power plants, calculated on the basis of our observations in their environment, ranges from 0.5 to 7Ci per year.
    • The Effect of Fossil Fuel and Biogenic CO, on the 13C and 14C Content of Atmospheric Carbon Dioxide

      Mook, W. G. (American Journal of Science, 1980-01-01)
      The normalization of a measured delta-14C value of atmospheric CO2 to a delta-13C value of -25 per mil does not take into account the presence of fossil fuel and biogenic CO2. In this paper, we try to assess these contaminations as well as the proper 14C content of "clean air".
    • Temporal Variations in Cosmogenic 10Be Production: Implications for Radiocarbon Dating

      Raisbeck, G. M.; Yiou, Françoise (American Journal of Science, 1980-01-01)
      A procedure is outlined for using cosmogenic 10Be variations in polar ice cores and lake or inland sea sediments to correct for 14C production variations in the past. Some of the requirements and problems associated with such a procedure are discussed.
    • Tree-Ring Dating and Radiocarbon Calibration in South-Central Europe

      Becker, Bernd (American Journal of Science, 1980-01-01)
      Radiocarbon variations between 3900 and 2800 BC have been established in La Jolla and Groningen using oak tree rings from a 2350-year floating oak series. Comparison of these variations with the bristlecone pine 14C variations provides precise ages for tree-ring dates of Neolithic settlements of Switzerland and Germany over a period of 1400 years. 14C variations measured in Heidelberg in absolutely dated oakring series from AD 250 to 720 show trends similar to those of long-term growth variation of oaks during the same period of time. The influence of the climatic regime on oak growth of this period is discussed.
    • The Radiocarbon Record in Tree Rings of the Last 8000 Years

      Suess, H. E. (American Journal of Science, 1980-01-01)
      It has become generally accepted during the last year that 14C fluctuations, the so-called "wiggles", observed in wood, dated by its tree rings, do indeed exist. Furthermore the La Jolla measurements show that apart from experimental noise, they do not represent random red noise, but characteristic, recurring features. In 1971, Houtermans found indications for the existence of cyclic components and recent Fourier analyses of all the available data by Neftel and Hartwig show a 200-year component. Cyclic oscillations with other periods appear to be present during limited time intervals. The character of the oscillations is not harmonic. The time derivative of many fluctuations is remarkably constant and such that the 14C rises by 1 percent in about 20 years and decreases by 1 percent in slightly more than twice that length of time. The properties of the overall radiocarbon record have to be considered in attempts to explain the variations in terms of variations of the cosmic ray-production rate and changes of the geochemical distribution of radiocarbon.
    • 14C and Other Parameters During the Younger Dryas Cold Phase

      Oeschger, Hans; Welten, Max; Eicher, Ulrich; Möll, Markus; Riesen, Trudi; Siegenthaler, Ulrich; Wegmüller, Samuel (American Journal of Science, 1980-01-01)
      Pollen analysis as well as 18O/16O results on lake marl show that the Younger Dryas climatic period, between about 11,000 and 10,300 BP, was the last vigorous cold phase of the Wurm Glacial. Detailed 14C analyses from a peat bog near Wachseldorn (Switzerland) point to a 14C anomaly in this period. Further indication of a 14C anomaly is given by the observation that, during the Younger Dryas period, the sedimentation rates in several lakes apparently were higher than in adjacent periods; an explanation might be that the 14C time scale was compressed between 11,000 and 10,000 BP, ie, the atmospheric 14C/C ratio varied. If real, this suggested 14C variation would probably be connected to the climatic events during this transition period from Later Glacial to Postglacial.
    • High Precision Radiocarbon Dating by Liquid. Scintillation Counting Applied to Radiocarbon Timescale Calibration

      Pearson, G. W. (American Journal of Science, 1980-01-01)
      The precision quoted on a radiocarbon date is often misleading. Improvement in the accuracy of measurement is discussed together with the use of appropriate precisions. The effect of high accuracy in 14C dating and meaningful precisions are illustrated and applied to radiocarbon time-scale calibration. Intercomparison of such calibrations reveals a significant continuous saw-tooth pattern of short-term periodicity.