• 14C Ages and Magnetic Stratigraphy in Three Australian Maars

      Barton, C. E.; Potach, H. A. (American Journal of Science, 1980-01-01)
      Detailed radiocarbon chronologies from three volcanic crater lakes (maars) in southeast Australia are examined in relationship to the magnetic mineral stratigraphies within lakes, and the magnetic secular variation stratigraphy between lakes. Some implications for magnetic dating are considered.
    • 14C Dating of Recent Crustal Movements in the Persian Gulf and the Iranian Makran

      Vita-Finzi, Claudio (American Journal of Science, 1980-01-01)
      Radiocarbon dating of mollusks and barnacles from fossil shoreline deposits in the Persian Gulf and on the coast of Iranian Makran is being used to assess the extent and rate of recent crustal deformation in the area. Samples are selected with the help of x-ray diffraction and of light and scanning electron microscopy; whenever possible, two or more ages are determined for each locality on monospecific samples. Age/height values have been used to compute local uplift rates by allowing for sea-level fluctuations, but eustatic controversy can be avoided by limiting the analysis to fault chronology and to relative vertical movements between dated sections. Short counting times on large, carefully pretreated samples would supply the numerous, cheap, low-resolution ages required to follow up the preliminary results obtained by the survey.
    • 14C in the Southern Indian Ocean

      Geyh, M. A. (American Journal of Science, 1980-01-01)
      14C measurements were carried out on sea water samples collected in 1973, in the Indian ocean. The results obtained for 9 vertical profiles between 27 degrees S and 48 degrees S are presented. In surface water, the bomb 14C content is maximum at middle latitudes. A time lag relative to the north hemisphere bomb 14C delivery is apparent. In the more southern latitudes, 14C content remains very low.
    • 14C Interlaboratory Comparison in the UK: Experiment Design, Preparation, and Preliminary Results

      Otlet, R. L.; Walker, A. J.; Hewson, A. D.; Burleigh, R. (American Journal of Science, 1980-01-01)
      An interlaboratory comparison experiment for 14C measurements has been organized jointly by the Harwell and British Museum laboratories to include the working radiocarbon laboratories of the United Kingdom. The experiment has been run along the lines of that organized by the IAEA for tritium and has explored the problems of sample preparation, verification of equivalent levels, and presentation of results. Samples of benzene representing 5 age equivalent levels between twice modern and 20,000 years old have been prepared and distributed for measurement either by direct counting (liquid scintillation) or full process tests. Preliminary results received show excellent agreement both between laboratories and in comparison with the known relative activities of the prepared solutions. The possibility of extending the experiment to cover different sample types and a wider distribution of testing laboratories is briefly discussed.
    • Age Structure of Holocene Coastal Sediments: Gulf of Carpentaria, Australia

      Rhodes, E. G.; Polach, H. A.; Thom, B. G.; Wilson, S. R. (American Journal of Science, 1980-01-01)
      Shells in beach-ridge and chenier Holocene deposits from the Gulf of Carpentaria, Queensland, have been dated by radiocarbon. Possible contamination of carbonate by post-depositional diagenetic processes, isotopic fractionation, ocean reservoir environmental effect, and association of biological age of sample material with depositional event have been examined in order to validate dating of samples from this environment. A numerical methodology used for comparing 'groups' of 14C dates strongly supports morphostratigraphic evidence that time discontinuities occur within both chenier and beach-ridge sequences. Four episodes are recognized in each area, all younger than ca 5800 years ago, the time when sea level reached its postglacial maximum in the Gulf of Carpentaria. To some extent, these episodes are out of phase, reflecting different modes of strandline accumulation.
    • Ages of Charcoal Samples of Geomorphological Interest in Northeast Hungary

      Csongor, Eva; Borsy, Zoltán; Szabó, Ilona (American Journal of Science, 1980-01-01)
      There are extended wind-blown sand territories in the northeastern part of the Great Hungarian Plain. Wind-blown sand migration periods were distinguished by means of radiocarbon age determination of charcoal samples found in the same type of a thin soil layer of chernozem character in different sand dune exposures. The ages of the samples were determined by proportional counter, and are around 12,000 years BP. This thin fossil soil layer, which is regionally spread in the northeast Hungarian wind-blown sand areas, presents a chronological mark between the blown sand forms evolved in the last glacial period and in the Holocene.
    • Bomb-Produced Carbon-14 in the Surface Water of the Pacific Ocean

      Linick, T. W. (American Journal of Science, 1980-01-01)
      The distribution of 14C concentrations in the dissolved inorganic carbon in the surface waters of the Pacific Ocean is shown to have a primarily latitudinal pattern with Delta-14C maxima at mid-latitudes in both hemispheres and a minimum at the equator. Oceanographic causes of this phenomenon are discussed.
    • Book Review: Relative Dating of the Fossil Hominids of Europe, K. P. Oakley

      Burleigh, Richard (American Journal of Science, 1980-01-01)
    • Carbon Isotope Measurement as an Index of Soil Development

      Ladyman, S. J.; Harkness, D. D. (American Journal of Science, 1980-01-01)
      14C and 13C enrichment values are reported for a series of surface soil profiles which represent the progressive transition from mor to mull humus induced by birch (Betula pendula) colonization. Variations in Deltaand delta-13C, which range between 85 to 154 ppm modern and -28.1 to -25.3 ppm (PDB), respectively, reflect changes in the rate and mode of organic decomposition. The most marked alterations in soil character occur over the first few decades following the introduction of birch, with clear isotopic evidence for the deeper penetration and accelerated mineralization of organic material.
    • Carbon-14 and Carbon-13 in Soil CO2

      Dörr, Helmut; Münnich, Karl Otto (American Journal of Science, 1980-01-01)
      Carbon isotope measurements in soil CO2 are presented and discussed. Soil CO2 concentration and 13C profiles were measured using a new technique. A simple model describing the CO2 transport from the soil to the atmosphere is derived. The finding that CO, in the soil is richer in 13C than the CO2 leaving the soil is attributed to isotopic fractionation in molecular diffusion.
    • Climate Periods in Trees and a Sea Sediment Core

      Pandolfi, L. J.; Kalil, E. L.; Doose, Paul Robin; Levine, L. H.; Libby, L. M. (American Journal of Science, 1980-01-01)
      Chemical components in a sea sediment core from the Santa Barbara Basin show the same periodic variations as do stable isotope variations in a Japanese cedar.
    • Content of 14C in Marine Mammals from Northern Europe

      Olsson, Ingrid U. (American Journal of Science, 1980-01-01)
      The reservoir effect of Scandinavian sea water has been determined by dating seals and whales killed well before man's impact on the natural 14C concentration became significant. The samples were collected at different places along the Swedish coasts and in the Gulf of Finland. They derive from AD 1657 or 1658, 1868, 1875, 1894, and 1906. The EDTA treatment of bones was used to obtain collagen free from contaminants. An elk, originating from AD 1881 was selected for comparison. A seal from AD 1899 from the Caspian Sea was also included in the investigation. All results have been normalized to delta-13C = -25 per mil vs PDB. The determinations yield values of the reservoir effect in agreement with earlier results obtained from shells and mammals. The final results are discussed in light of previous variations of 14C content in the atmosphere. Using a smoother curve, the reservoir effect is slightly smaller than was hitherto believed. An event thought to be of cosmic origin caused the count rate of both proportional and Geiger counters to increase significantly around December 4, 1978. The correction for this has been studied. The statistics for background, oxalic acid, and unknown samples, measured repeatedly after this correction, were as good as usual.
    • Direct Detection of 14C at the Harwell Tandem

      Shea, J. H.; Conlon, T. W.; Asher, James; Read, P. M. (American Journal of Science, 1980-01-01)
      Direct detection of 14C using the Harwell 6MV Tandem accelerator has been achieved using a gaseous ion source. The implications of our results for the use of such sources in this role and for the machine, in general, are discussed.
    • Exploratory Analysis of the International Radiocarbon Cross-Calibration Data: Consensus Values and Interlaboratory Error: Preliminary Note

      Currie, L. A.; Polach, H. A. (American Journal of Science, 1980-01-01)
      A preliminary review is given of the evaluation of the International Cross-Calibration Radiocarbon Data. Consensus values and standard errors are D14C = 508.1 +/- 2.0 per mil (ANU Sucrose) and Delta = -2.5 +/- 1.5 per mil, (1850 Wood). Reporting format follows recornmendations of Stuiver and Polach (1977).
    • Gas Exchange Rate Measurements in Natural Systems

      Broecker, W. S.; Peng, T.-H.; Mathieu, G.; Hesslein, R.; Torgersen, T. (American Journal of Science, 1980-01-01)
      Rates of CO, exchange across the air-water interface in oceans and lakes measured to date by the L-DGO group are summarized. They range from 3 to 38 moles/m2/yr. The possible causes for this range include the differences in salinity, mean wind speed, and pH. Wind tunnel studies comparing fresh water and sea water are required before a satisfactory explanation can be found.
    • Holocene Sea-Level History: Case Study of the Statistical Evaluation of 14C Dates

      Geyh, M. A. (American Journal of Science, 1980-01-01)
      The limits of the statistical evaluation of 14C dates by histograms are discussed. The method of the attempt to establish a global chronology of the shortterm eustatic sea-level changes during the Holocene is examined as well as its correlation with the precisely determined Suess wiggles.
    • Hydrological Implications from 14C Profiling of UK Tufa

      Thorpe, P. M.; Otlet, R. L.; Sweeting, M. M. (American Journal of Science, 1980-01-01)
      Tufa is a superficial, secondary deposit of calcium carbonate which accumulates on precipitation from emergent spring waters. It occurs as discrete, localized masses in regions of calcareous country rock. In the United Kingdom, deposits vary widely in structure and thickness but little is known of the rate of deposition. Some deposits contain laminae assumed to represent annual growth increments and which should contain a 14C and stable isotope record related to the original water from which it was precipitated. Investigations are reported on tufa from three areas of different limestones in the United Kingdom (Northwest Yorkshire, South Derbyshire and North Oxfordshire). Hydrologically, the dating of tufa by 14C involves the same problems as the dating of groundwater. In the case of actively forming tufa, however, it is possible to derive a sequence of measurements, beginning with present day deposition, which clearly demonstrates the applications of age corrections. At Gordale Scar, Northwest Yorkshire, a profiling study of laminated tufa appears to show bomb trial 14C to a depth of 18mm below the surface, with almost constant values around 50 percent modern (raw data) from 18 to 48mm below the surface. The 14C content of surface tufa lies within the seasonal range of 14C measurements from the parent stream waters. Results of 50 percent modern in the sequence are consistent with the simplest correction procedures based on delta-13C balance and the observed delta-13C change on tufa precipitation is a practical demonstration of the fractionation factor e13. However, the application of corrections to active, surface tufa and parent waters collected monthly over a period of study (14 months) from all three sites, produce results higher than would be expected from published world 14C levels.
    • Isotopic Fractionation of Norwegian Materials for Radiocarbon Dating

      Gulliksen, Steinar (American Journal of Science, 1980-01-01)
      To improve reporting of radiocarbon dates, Stuiver and Polach (1977) recommend that reported standard errors should include the error in the applied delta-13C value, and suggest estimated mean values for delta-13C to be applied when not measured. Based on delta-13C data for ca 250 samples measured during 1975-1979, mean values for different materials dated by the Trondheim radiocarbon laboratory have been compiled. All material is from Norway and Svalbard (marine bone collagen). For peat, gyttja, and terrestrial bone material, delta-13C should be measured to obtain optimal precision in the dates. For shell, wood, charcoal, and marine bones, the standard error in an estimated delta-13C value will only increase uncertainty of a date from +/- 50 years to ca +/- 55 years.
    • MACS: An Accelerator-Based Radioisotope Measuring System

      Purser, Kenneth H.; Liebert, Reuel B.; Russo, Carl J. (American Journal of Science, 1980-01-01)
      A description is given of an accelerator-based radioisotope measuring system, being supplied to the Universities of Arizona and Toronto and in part to the University of Oxford. This system will be capable of measuring 14C/12C and 14C/12C ratios in milligram samples of cracked acetylene. At present 200 micrograms of carbon obtained from cracked acetylene appears to be adequate for an isotopic ratio determination. Previous performance and new calculations indicate that a precision better than 1 percent will be achieved in a half-hour period only limited by counting statistics. A precision of 0.2 percent will be obtained in a ten-hour period. Using a carbon sample with an age greater than 60,000 years, the measured background 14C/12C ratio will be less than 0.07 percent of modern.
    • Modeling the Carbon System

      Broecker, Wallace S.; Peng, Tsung-Hung; Engh, Richard (American Journal of Science, 1980-01-01)
      Claims that forest cutting (luring the last few decades has contributed significantly to the buildup in atmospheric CO2 have cast doubt on the validity of models used to estimate CO2 uptake by the ocean. In this paper we review the existing models and conclude that the box-diffusion model of Oeschger and his co-workers provides an excellent fit to the average distributions of natural and bomb-produced radiocarbon. We also take the first steps toward a more detailed ocean model which takes into account upwelling in the equatorial zone and deep water formation in the polar zone. The model is calibrated using the distribution of bomb-produced and cosmic ray-produced radiocarbon in the ocean. Preliminary calculations indicate that the fossil fuel CO2 uptake by this model will be greater than that by the box-diffusion model of Oeschger and others (1975) but not great enough to accommodate a significant decline in the mass of the terrestrial biosphere over the past two decades.