• New National Bureau of Standards Contemporary Carbon-14 Standards

      Cavallo, L. M.; Mann, W. B. (American Journal of Science, 1980-01-01)
    • On the 14C to Tritium Relationship in the North Atlantic Ocean

      Roether, Wolfgang; Münnich, Karl-Otto; Schoch, Hildegard (American Journal of Science, 1980-01-01)
      Nuclear-weapon produced 14C (or bomb 14C) in the ocean can be traced by simultaneous tritium observations. Data are presented on the general relationship of bomb 14C and tritium in the North Atlantic. For the period 1965 to 1973, the excess 14C to tritium ratios in the surface water vary, systematically, over a factor of 10: the ratios monotonically increase with time, and decrease with latitude, particularly so for the later observations. The sub-surface water ratios show that the midand low-latitude water below about the 15 degrees C isothermal horizon (~500m depth) originates from higher northern latitudes, rather than being renewed by local vertical mixing. It is further shown that in the North Atlantic, bomb 14C did not penetrate beyond the horizon where the presently observed 14C concentration is Delta-14C = -75 per mil. Observed concentrations up to about -40 per mil can be corrected for a bomb contribution if the tritium concentration is known because the bomb 14C to tritium concentration ratio is rather uniform in this range. A surface water 14C concentration versus time curve is presented for the period since 1957. This curve is based on a North Atlantic mixing model and is fitted to the 14C observations. Making use of a previously published tritium versus time curve obtained by the same model, a time curve for the average excess 14C to tritium ratio in North Atlantic surface water is given. This curve reproduces the observations well. The presented data and theoretical curves show the usefulness of simultaneous 14C and tritium observations for mixing studies and to provide corrections for bomb 14C in sub-surface 14C data in the North Atlantic.
    • Paleoclimatic Evidence in Apparent 14C Ages of Saharian Groundwaters

      Sonntag, Christian; Thorweihe, Ulf; Rudolph, Jochen; Löhnert, E. P.; Junghans, Christel; Münnich, K. O.; Klitzsch, Eberhard; El Shazly, E. M.; Swailem, F. M. (American Journal of Science, 1980-01-01)
      Frequency distributions of more than 300 14C groundwater ages from various regions in northern and southern Sahara reflect the alternating sequence of humid and arid periods in the Sahara during the Holocene and late Pleistocene. A broad frequency maximum between 20,000 and 50,000 years BP indicates a long humid period. During this time span, the northern Sahara received rain from the Western Drift, which is concluded from a west-east decrease of deuterium and oxygen 18 of these groundwaters (continental effect). In the time-slice between 14,000 and 20,000 years BP, groundwater formation was significantly lower due to a cool and (semi-)arid period. In the Holocene, the Saharian climate is characterized by a sequence of dry and wet periods.
    • Progress in Radiocarbon Dating with the Chalk River MP Tandem Accelerator

      Andrews, H. R.; Ball, G. C.; Brown, R. M.; Davies, W. G.; Imahori, Yoshio; Milton, J. D. (American Journal of Science, 1980-01-01)
      The evolution of a tandem accelerator 14C dating system at Chalk River is recounted. Background problems and sources of instability are discussed and solutions are described. Details of sample chemistry and source preparation are presented.
    • Radiocarbon Activity Measurements of Oolitic Sediments from the Persian Gulf

      Šilar, Jan (American Journal of Science, 1980-01-01)
      Radiocarbon activity of successive parts of Pleistocene and Holocene ooids and mollusk shells from the Persian Gulf, Kuwait, was measured. The inner part of the ooids showed the lowest activity and the cement between grains the highest. Radiocarbon activities correspond to the general stratigraphy and to the position of the sediments. Radiocarbon ages of Pleistocene sediments seem to be very low due to recrystallization of aragonite. Higher radiocarbon activity of cement indicates that atmospheric carbon dioxide was involved in the subaerial diagenetic process. The radiocarbon age of well-preserved mollusk shells seems to be lower than their allegedly Pleistocene geologic age.
    • Radiocarbon Concentration in the Atmosphere: 8000-Year Record of Variations in Tree Rings: First Results of a USA Workshop

      Klein, Jeffrey; Lerman, Juan Carlos; Damon, Paul E.; Linick, Timothy (American Journal of Science, 1980-01-01)
    • Radiocarbon Dating by Ion Counting: Proposals and Progress

      Hedges, R. E. M.; White, N. R.; Wand, J. O.; Hall, E. T. (American Journal of Science, 1980-01-01)
      In the two years since the first successful measurements of 14C by high energy mass spectrometry, the advantages and the basic techniques of the method have been sufficiently reported. They will not be repeated here. This paper describes the work being done at Oxford to fill the gap between demonstrating the effectiveness of the approach and the creation of a facility dedicated to the carbon dating of milligram samples.
    • Radiocarbon Dating of Calcareous Tufa: How Reliable Data Can We Expect?

      Srdoč, Dušan; Obelić, Bogomil; Hovatinčic, Nada; Sliepčević, Adela (American Journal of Science, 1980-01-01)
      Systematic dating of tufa samples has been undertaken to establish achronology of tufa deposits in Plitvice National Park, Yugoslavia. We conclude thattufa samples give reproducible data within the time span of 40,000 years up torecent. The 14C/12C ratio of carbon in the ambient biosphere and hydrosphere gives adetailed picture of the distribution of carbon isotopes in the investigated system.Despite the susceptibility of calcareous material to ambient conditions in the hydrosphere,the original 14C composition of tufa has not been substantially changed. Avertical profile which was cut in tufa during pathway construction showed that thetufa isochrones run vertically in the investigated area. The vertical isochrones and the14C gradient were horizontal due to tufa build-up in Plitvice National Park whichoccurs on vertical escarpments that have been flooded. The relatively uniform radiocarboncontent of most tufa deposits indicates redistribution of radiocarbon duringthe formation period. While detailed stratigraphy is often obscured, a general chronologyof tufa deposits in the investigated area has been established.
    • Radiocarbon Dating of Ceramic Materials: Progress and Prospects

      De Atley, Suzanne P. (American Journal of Science, 1980-01-01)
      Although initial studies in the 1960's established the feasibility of applying the radiocarbon technique directly to ceramics, subsequent analyses have revealed this category of materials to be more complex than previously believed. Consideration of the points at which various types of organic carbon are introduced into ceramic materials by natural or human agencies allows more effective screening of potential sherd samples. It also suggest ways to overcome some of the limiting factors involved in dating ceramics.
    • Radiocarbon Dating of Earthquakes

      Berger, Rainer; Kaufman, T. S. (American Journal of Science, 1980-01-01)
    • 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 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.
    • 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.
    • 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).
    • 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.
    • 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)
    • 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.
    • 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.
    • 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.