• Workshop on 14C Reporting

      Stuiver, Minze (American Journal of Science, 1980-01-01)
    • W. F. Libby and the Archaeologists, 1946-1948

      Marlowe, Greg (American Journal of Science, 1980-01-01)
      Archaeologists began to participate in cross-disciplinary endeavors in the 1930's, albeit on a very limited basis. The passage of time found members of that discipline unprepared for collaboration with physical scientists when W F Libby announced the development of the radiocarbon dating method. Libby proposed to apply to archeologic and geologic samples techniques based on ideas that were completely foreign to archeology.... The initial reactions of archeologists were sometimes amusing but more often significant, for they led to the foundation and emergence of the radiocarbon chronology that has so profoundly affected our understanding of prehistory (Johnson, 1967, p 165). To date, our historical knowledge about the nature, function, and impact of the early (1946-1948) relations between Libby and American archaeologists has come to us in the form of published anecdotes, many of which contain inaccurate information. The author's access to W F Libby's private 14C correspondence, combined with data obtained from interviews with some of the principal participants throughout this period, offers many new or different insights into the nascent years of radiocarbon dating. When, and under what unexpected cricumstances, did Libby first encounter representatives of the achaeologic community? What strategies were employed to facilitate diffusion of knowledge about 14C dating across disciplinary boundaries? How did archaeologists respond to the introduction or "intrusion" into their field of Libby's radioactive age-measurement tool?
    • Vertical Advection—Diffusion Rates in the Oceanic Thermocline Determined from 14C Distributions

      Quay, P. D.; Stuiver, Minze (American Journal of Science, 1980-01-01)
      The characteristics of a one-dimensional vertical advection-diffusion ocean mixing model were examined using temperature, salinity, and bomb 14C measurements made during the GEOSECS program. Vertical advection (W) and eddy diffusion (K) rates for the main oceanic thermocliine and CO2 gas exchange rates (E) were determined from the depth distributions of salinity and bomb produced 14C measured in the upper 1000m of the Atlantic and Pacific Oceans. In the Atlantic, the results suggest that vertical diffusion rates are lower in the equatorial region (K = 0.6cm2sec-1) than in the temperate region (K = 1.6cm2sec-1). Upwelling rates were calculated for stations located between about 30 degrees N and 30 degrees S and average 10m yr-1, corresponding to an upward transport of about 10 Sverdrups. Model calculations of the gas exchange rate of CO2 indicate a 2 to 3-fold decrease between temperate latitudes and the equatorial latitudes of the Atlantic. For many of the Pacific GEOSECS stations, the Delta-14C depth distribution is distinctly different than in the Atlantic, and cannot be used to calculate unique values of K and W that explain both the salinity and 14C depth distributions.
    • Use of 39Ar and 14C for Groundwater Dating

      Loosli, Heinz Hugo; Oeschger, Hans (American Journal of Science, 1980-01-01)
      Cosmic-ray produced atmospheric 39Ar activity (T1/2 = 269 yr) has been determined at 0.11 +/- 0.012 dpm/lt argon. Ice samples from two profiles in Greenland bore holes showed conclusively that 39Ar dating leads to correct ages. Corrections can be made for possible contamination of the samples with ambient air during field extraction and during laboratory processing by measuring 85Kr in the same samples. The following isotopes: 14C, 39Ar, 85Kr, 3H, partly 32Si, 13C, and 18O were investigated in 20 groundwater samples. Unexpectedly large discrepancies between "14C ages" and "39Ar ages" were observed for many of these samples. For example, a horizontal profile of a confined sandstone aquifer in the Franconian Albvorland showed decreasing 39Ar and 14C activities from respectively, 100 percent to 17 percent and 80 percent to 0.3 percent of modern activity, corresponding to elapsed time periods of 700 and >20,000 years, respectively. It seems unlikely that gas exchange through the aquiclude is the cause of this discrepancy. It can neither be explained by only assuming that the water represents a mixing of components with different ages. We detected the possibility of underground production of 39Ar in thermal spring water from Zurzach, Switzerland. Its argon showed higher specific activity than atmospheric argon. Elsewhere, however, samples were found containing no detectable 39Ar activity: two wells of a confined carstic aquifer in Ingolstadt, Germany, show less than 7 percent atmospheric activity. In our opinion, the assumptions on which the 14C method in hydrology are based need to be critically re-examined. It is possible that for some aquifers carbonate exchange between solid and liquid phases in the aquifer changes 14C results to a larger degree than generally assumed.
    • Unreliability of 14C Dates from Organic Matter of Soils

      Gilet-Blein, Nicole; Marien, Gérard; Evin, Jacques (American Journal of Science, 1980-01-01)
      Contamination by recent carbon and the turnover of organic matter make dating of ancient soils difficult. In order to isolate the oldest organic fraction of sediments, two main extraction methods were previously proposed: 1) alkaline solubilization of humus that separates humins, humic acids, and fulvic acids, and 2) successive hydrolyses that solubilize increasingly resisting products. Both preparation methods were tested on the same actual or fossil soils of different pedologic types from five geologic profiles on which other chronologic data are available. Analytic results show that 14C ages obtained from alkaline extraction products differ according to the duration of treatments and characteristics of soils: while hydrolysis should yield more homogeneous results and isolate oldest fractions. It seems likely that true ages of geologic formations were never obtained from their organic matter and that the oldest organic fraction, contemporaneous with the sediment formation, completely disappears. Thus, most ages from 14C dating of organic matter of soils must be too recent.
    • The Use of Radiocarbon to Measure the Effects of Earthworms on Soil Development

      Stout, J. D.; Goh, K. M. (American Journal of Science, 1980-01-01)
      Delta-14C and delta-13C values for organic matter in forest and grassland soils, in the presence or absence of earthworms, indicate that it should be possible to quantify the effects of earthworms on soil organic matter by this means. Without earthworms, both in forest and grassland soils, plant debris tends to accumulate on the surface of the mineral soil and little organic matter is incorporated into or is translocated down the soil profile. Where earthworms are present, there is much more marked incorporation of fresh plant debris in the mineral soil. This is shown especially by the pulse of `bomb' carbon and also by the delta-13C values.
    • Transfer of Bomb 14C to the Ocean Surface

      Nydal, Reidar; Lövseth, Knut; Skogseth, Fred H. (American Journal of Science, 1980-01-01)
      Additional 14C data from the atmosphere and ocean have been provided since the ninth 14C conference in 1976. At the moment, one sampling station in the troposphere in each hemisphere seems to give sufficient accuracy for exchange studies. The 14C concentration in the troposphere in December 1978 constituted a mean value of 30 +/- 1 percent (∆14C) above normal level, a concentration that has been reduced to about one half during 12 years, 14C measurements have been performed with intervals of 1 to 4 months in the surface water of the Atlantic, Pacific, and Indian Oceans. In addition to the 14C data observed, the salinity and temperature are also measured. Because of earlier objections against storing sea water in steel drums on board ships for months before treatment, the CO2 has now been flushed out immediately after collection. The reliability of previous measurements has been confirmed with 10 parallel samples. 14C concentration in ocean surface on each location shows some seasonal variation due to variable exchange of water with deeper layers.
    • The First 20 Years of Radiocarbon Dating

      Polach, Dilette (American Journal of Science, 1980-01-01)
      A bibliography of the radiocarbon dating literature for the years 194868, which is in the process of compilation, is examined and a format is proposed. A survey of literature growth has also been undertaken. This enables projections of the numbers of publications referring to radiocarbon dating to be made. The estimated number of publications for the year 1978 is compared to literature retrieval obtained by interrogating eight relevant computer data bases. It is concluded that computer information retrieval is not satisfactory. Bibliographic control of radiocarbon dating literature would be best achieved by a bibliography dedicated to the subject and updated at regular intervals.
    • The Climate History of the Eastern Mediterranean as Recorded in Mollusk Shells

      Kaufman, Aaron; Magaritz, Mordeckai (American Journal of Science, 1980-01-01)
      An 18O/16O versus 14C age curve was constructed for unrecrystallized Holocene marine shell samples from Israel that were shown to be homogeneous populations. The surprisingly large variation in the oxygen isotopic composition (1.2 per mil) between 2600 and 4000 years ago is most probably due to variations in the isotopic composition of the water. This implies that either the excess of evaporation over precipitation or the Nile river discharge must have varied significantly during the Holocene.
    • The Behavior of 14C and 13C in Estuarine Water: Effects of In Situ CO2 Production and Atmospheric Change

      Spiker, Elliott (American Journal of Science, 1980-01-01)
      The effects of nonconservative sources (inputs) and sinks (outputs) of carbon are indicated by the behavior of Delta-14C and delta-13C of the total dissolved inorganic carbon (Sigma-CO2) in San Francisco Bay and Chesapeake Bay. Isotopic distributions and model calculations indicate that in North San Francisco Bay the net CO2 flux to the atmosphere and carbon utilization in the water column are balanced by benthic production. Municipal waste appears to be a dominant source in South San Francisco Bay. In Chesapeake Bay, atmospheric exchange has increased the Delta-14C and delta-13C in the surface water. Decomposition of organic matter in the water column is indicated to be the dominant source of excess Sigma-CO2 in the deep water.
    • Studies on the Loess Deposits of the Kashmir Valley and 14C Dating

      Kusumgar, Sheela; Agrawal, D. P.; Krishnamurthy, R. V. (American Journal of Science, 1980-01-01)
      The loessic deposits along with their palaeosols of the Kashmir Valley have been 14C dated using both organic and carbonate fractions. The 14C dates on both the fractions show good concordance. The 14C dates indicate that the last deglaciation in Kashmir (34 degrees N) already started ca 18,000 +/- 1000 BP at ca 1600m and ca 15,000 BP at ca 3000m altitude and thus support the recent global evidence of deglaciation having started several millennia before the Holocene.
    • Soil Dating by Fractional Extraction of Humic Acid

      Kigoshi, Kunihiko; Suzuki, Nobuko; Shiraki, Mari (American Journal of Science, 1980-01-01)
      The addition of organic materials derived from the upper soil layer yields, for samples at greater depth, younger 14C dates than the date of deposition. To find a criterion for the contamination with younger carbon in a soil sample, we examined the radiocarbon concentrations in two humic acid fractions and humin taken from the same sample. The humic acid extracted from a soil sample was divided into two fractions HA1 and HA2. HA1 is the first fraction extracted by 30 minutes' heating with 2 percent NaOH solution, and HA2 is the second fraction extracted by 2 hours' heating with 2 percent NaOH solution after the extraction of HA1. The residue was assumed as the humin (HM). Many of the peat or soil samples taken from the layer just above the nonpermeable layer contain appreciable amounts of organic materials transported from the upper layer after the sedimentation of the deposits. For the limited number of cases tested here, there is a trend in which the contaminants are selectively extracted by HAl or HA2. When the soil samples are contaminated the ages of the HA1 and HA2 fractions appeared to differ widely in most cases. Agreement between the HA1, HA2, and HM ages may be used as a criterion for the reliability of the soil dating.
    • Search for Pedogenic Phases During Younger Pleistocene and Holocene (Soltanien and Rharbien) of Tunisia

      Scharpenseel, H. W.; Zakosek, Heinrich; Neue, Ulrich; Schiffmann, Heinrich (American Journal of Science, 1980-01-01)
      Radiocarbon dates, obtained from paleosols, sediments, fossils, and groundwater samples of North Africa and especially, Tunisia, were investigated for information on phases of pedogenesis throughout the younger Pleistocene and Holocene in north and central Tunisia. This paper evaluates available data, while a larger set of new samples is under study, which, hopefully will exhaust the problem and will reveal whether extrapolations such as those made in this paper, eg, phases of pedogenesis from groundwater data, are correct. Frequency distribution of the dates from groundwaters taken by systematic sampling, as well as from random soil samples from open pits that yielded access to buried paleosols, indicate that organic matter was being produced for 7 or 8 periods. The evidence suggests major pedogenic activity at about 2000 BP, 4000 to 6004 BP, 8000 to 12,000 BP, and perhaps 21,000 to 25,000 BP.
    • Report on the Workshop on the Calibration of the Radiocarbon Time Scale

      Damon, P. E.; Lerman, J. C.; Long, Austin; Bannister, Bryant; Klein, Jeffrey; Linick, Timothy (American Journal of Science, 1980-01-01)
    • Radiometric Dating with University of Washington Tandem Van de Graaff Accelerator

      Farwell, G. W.; Schaad, T. P.; Schmidt, F. H.; Tsang, M.-Y. B.; Grootes, P. M.; Stuiver, Minze (American Journal of Science, 1980-01-01)
      The University of Washington Model FN tandem Van de Graaff accelerator is being used for the measurement of extremely small isotopic ratios, notably 14C/12C and 10Be/9Be, in a joint project of the Nuclear Physics Laboratory (NPL) and the Quaternary Isotope Laboratory (QL). The experimental arrangements and technical developments are described, and some preliminary results on isotopic ratios in carbon and beryllium are presented.
    • Radioisotope Detection with the Argonne FN Tandem Accelerator

      Kutschera, Walter; Henning, Walter; Paul, Michael; Stephenson, C. J.; Yntema, J. L. (American Journal of Science, 1980-01-01)
      A standard heavy ion nuclear structure facility has been used to detect several long-lived radioisotopes by counting the accelerated ions. The problem of eliminating strong isobaric background beams has been solved by combining the energy loss dispersion through a uniform Al foil stack with the high momentum resolution of an Enge split-pole magnetic spectrograph. Radioisotope concentrations in the following ranges have been measured: 14C/12C = 10^(-12) to 10^(-13), 29Al/27Al = 10^(-10) to 10^(-12), 32Si/Si = 10^(-8) to 10^(-14), 36Cl/Cl = 10^(-8) to 10^(-11).
    • Radiocarbon Dating of Pleistocene Bone: Toward Criteria for the Selection of Samples

      Taylor, R. E. (American Journal of Science, 1980-01-01)
      Amino acid composition data and stable isotope ratios (14N, D, and 13C) are being evaluated as sources of information to indicate the presence of non-indigenous organics in bone samples intended for 14C analyses. The study is being conducted in the context of the planned measurement of Pleistocene bone samples by a high energy mass spectrometric 14C detection system.
    • Radiocarbon Evidence for Holocene Recharge of Ground Water, Western Desert, Egypt

      Haynes, C. V.; Haas, Herbert (American Journal of Science, 1980-01-01)
      During Pleistocene pluvial precipitation was sufficient for the maintenance of groundwater supported lakes and for the accumulation of playa lakes in wind-scoured depressions during the early Holocene pluvial. At places where ground water reaches near to the surface, wells (birs) have been dug and maintained in historic times. These birs have been used as sampling sites for water analyses, including carbon-14 levels, carbon and oxygen stable isotope ratios, tritium concentrations, and chemical data. All the waters from birs analyzed to date produced apparent radiocarbon ages ranging from late historic to early Holocene, and tritium analyses on some of these indicate no recharge during the Atomic age. Sources of error for the radiocarbon analyses, including exchange with atmospheric CO2, respiration by plant roots, and contact with carbonates of considerably older age, were evaluated. None of these factors have such an extreme impact on the measurements as to render the result invalid. Two trends revealed by these data are an increase in apparent age from northwest to southwest and with subsequent extractions at the same site where the hand-dug well was bailed out and sampled four times within two days. We conclude that recharge of shallow ground water occurred in early Holocene time, and some recharge of deeper aquifers may have occurred where infiltration paths permitted. Some recharge occurred in late Holocene (post pluvial) time, but the net trend has been toward hyper-aridity that characterizes the area today.
    • Radiocarbon Dating with Tandem Electrostatic Accelerators

      Gove, N. E.; Elmore, David; Ferraro, R. D.; Beukens, R. P.; Chang, K. H.; Kilius, L. R.; Lee, H. W.; Litherland, A. E.; Purser, K. H.; Rubin, Meyer (American Journal of Science, 1980-01-01)
      An MP tandem Van de Graaff accelerator at the University of Rochester has been employed since May 1977 to detect 14C in various terrestrial samples. The carbon sample sizes required are lmg or less. Dating accuracies based on reproducibility now approach (+/- 80 years). Measurements have been made on 1850 wood, Australian sucrose, a carbon sample from Mt Shasta, a baby woolly mammoth, and an Egyptian bull mummy wrapping.