• Urban Atmospheric 14CO and 14CH4 Measurements by Accelerator Mass Spectrometry

      Klouda, G. A.; Currie, L. A.; Donahue, D. J.; Jull, A. J. T.; Naylor, M. H. (American Journal of Science, 1986-01-01)
      Atmospheric gas samples (0.1 m3) were collected at ground level during January/February 1984 in Las Vegas, Nevada for 14C/13C accelerator mass spectrometry and total abundance measurements of CO and CH4. During winter months in this locale, CO concentrations can occur at 10 to 100 times background, occasionally exceeding the National Ambient Air Quality Standard (NAAQS). Methane concentrations show a slight enhancement (-24%) above the background (non-urban troposphere) level. A comparison of CO and CH4 concentrations shows a good linear correlation which may indicate a common source. Preliminary 14C/13C results of the two species suggest that fossil emissions are the predominant source of excess CO and CH4 in the samples taken. Estimates of anthropogemc CO and CH4 are important for source apportionment of combustion emissions. In addition, this information is valuable for understanding the global CO and CH4 cycles and, therefore, human impact on climate and the stratospheric ozone layer.
    • Multiple Dating of a Long Flowstone Profile

      Geyh, Mebus A.; Hennig, G. J. (American Journal of Science, 1986-01-01)
      Dense speleothem samples are considered as closed systems and are, therefore, possibilities for any dating method. Four dating methods (14C, U/Th, paleomagnetism, and electron spin resonance = ESR) were used for samples up to 1,000,000 yr old and taken along a vertical flowstone profile in the Heggen cave in West Germany. Also delta-18O and delta-13C analyses were carried out. The reliability of the results of each method is dependent on the diagenetic processes that took place during the complex growth history of the flowstone. Speleothem growth was interrupted during glacial periods. During interglacial periods, at least the stalagmite growth rate was greater by one order of magnitude than during interstadial periods. During the periods of low interstadial growth rate various processes might have changed the 14C, 18O, and 13C concentrations, leaching might have removed uranium, recrystallization might have moved thorium several centimeters, and increased content of radon in the cave might have exaggerated the accumulated dose (AD) at the speleothem surface. As a result, 14C ages may be too small and U/Th as well as ESR data may be too large.
    • Operation of the NSF-Arizona Accelerator Facility for Radioisotope Analysis and Results from Selected Collaborative Research Projects

      Linick, T. W.; Jull, A. J. T.; Toolin, L. J.; Donahue, D. J. (American Journal of Science, 1986-01-01)
      Radiocarbon dating at the Arizona accelerator facility has improved substantially in the last three years. Since starting to use graphite targets (see Jull et al, 1986), we have been able to obtain routinely a precision of ca +/- 1 % (ca 80 yr) for relatively modern material. Our routine technique of tuning and operating the tandem accelerator mass spectrometer (TAMS) and our method of calculating 14C results are discussed in detail. Data on activity ratios of oxalic acid-II/oxalic-I are presented. Examples of the wide variety of projects on which we have collaborated are given. Brief discussions of three such projects are presented for our colleagues who were unable to attend this conference: an Arizona Indian archaeologic project, a study of megafaunal extinctions, and a study of the growth of phosphorite nodules on the sea floor off the Peruvian coast.
    • On the Initial 14C Activity of Karst Aquifers with Short Mean Residence Time

      Krajcar-Bronić, Ines; Horvatinčić, Nada; Srdoč, Dušan; Obelić, Bogomil (American Journal of Science, 1986-01-01)
      The 14C activity of total dissolved inorganic carbon (DIC) as well as tritium activity and stable isotope content (13C, 2H, 18O) of spring water were measured for 3 consecutive years at 3 karst springs that feed Plitvice Lakes, NW Yugoslavia. The constant chemical and stable isotope composition and temperature indicated well mixed aquifers. A very short mean residence time of underground water (2-5 yr) was determined by tritium activity measurements. Measured 14C activities of 3 karst springs varied from 60.0% to 82.5%. The measured 14C activities were compared with calculated 14C activities based on various models using measured values of 14C activity of soil at different depths and 13C content of limestone, plants, and soils from the recharge area. Our measurements indicate that recharge systems in karst aquifers are open to the atmosphere. The atmospheric CO2 contributes to the 13C content and the 14C activity of ground water to an estimated extent which varies between 10 and 40% of DIC.
    • Origins of Carbon in Potsherds

      Gabasio, Martine; Evin, Jacques; Arnal, Gaston Bernard; Andrieux, Philippe (American Journal of Science, 1986-01-01)
    • Production of Graphite Targets by Deposition from Co/H2 for Precision Accelerator 14C Measurements

      Jull, A. J. T.; Donahue, D. J.; Hatheway, A. L.; Linick, T. W.; Toolin, L. J. (American Journal of Science, 1986-01-01)
      A method has been developed at the Arizona AMS facility for production of graphite directly from CO2 by catalytic reduction of CO/H2 mixtures. The method is a modification of procedures discussed by Vogel et al (1984). Currents of 12C- from these targets vary considerably, but have a median value which is 70% of that achieved from spectroscopic graphite. Precisions of +/- 60 to 100 yr are routinely achieved for 14C ages of 5000-yr-old samples containing one milligram of carbon. The yield of 14C from "blank" targets is 0.6 +/- 0.1% of that from modern material.
    • Radiocarbon Activity Variation in Dated Tree Rings Grown in Mackenzie Delta

      Fan, C. Y.; Tie-Mei, Chen; Si-Xun, Y.; Kai-Mei, Dai (American Journal of Science, 1986-01-01)
      We measured the Delta-14C values in 57 rings (from AD 1824 to 1880) of a white spruce grown in Mackenzie Delta (68 degrees N, 130 degrees W), as part of our continuing study of the Delta-14C variation related to solar activities. The values exhibit a 10 per mil fluctuation with an 11-year periodicity anti-correlated with the solar activity cycle. We also measured the Delta-14C values in 6 rings (from AD 1940 to 1945). The abnormally high value in the 1943 ring may be due to two large solar flares occurring in 1942.
    • Radiocarbon Concentration of California Aerosols

      Berger, Rainer; McJunkin, David; Johnson, Roberta (American Journal of Science, 1986-01-01)
      In this study the origin of the carbonaceous fraction of total suspended particles (TSP) in air was analyzed. While the summer data show increasing carbon concentrations in the Los Angeles air basin from west to east, in the winter high levels of carbon particles can be found over the coast. The smallest and most dangerous particle fraction is principally composed of fossil carbon.
    • A 14C Electronic Measurement System with a Microcomputer

      Walanus, Adam (American Journal of Science, 1986-01-01)
      Even though the reliability of equipment has improved, the quality of measurement should still be checked. This task may be performed by a microcomputer with the physicist's intervention only when an error in measurement is detected.
    • Radiocarbon Dating of Sediments

      Fowler, Alison J.; Gillespie, Richard; Hedges, Robert M. (American Journal of Science, 1986-01-01)
    • Radiocarbon Dating of Lake Sediment from Two Karst Lakes in Yugoslavia

      Srdoč, Dušan; Obelić, Bogomil; Horvatinčić, Nada; Krajcar-Bronić, Ines; Marčenko, Elena; Merkt, Joseph; Wong, How Kin; Sliepčević, Adela (American Journal of Science, 1986-01-01)
      Samples of sediment cores from two lakes in the karst area of northwest Yugoslavia were analyzed. Both Lakes Kozjak and Prošće are in the Plitvice National Park, Central Croatia. 14C dating, sedimentologic, seismic, and isotopic studies, and distribution of diatoms are presented. 14C dating of lake marl revealed a uniforn sedimentation rate in Lake Prošće as opposed to Lake Kozjak. Both lake sediments belong to the Holocene period. 14C dating of lake sediment is in agreement with seismic profiles, sedimentologic analysis, and diatom frequency measurements both in an undisturbed as well as in a disturbed lake sediment.
    • A Study of Errors in 14C Dates of Peat and Sediment

      Olsson, Ingrid U. (American Journal of Science, 1986-01-01)
      It is a well-established fact that 14C dates from lake sediments are usually too old because of contamination with allochthonous material and/or due to discrete reservoir effects. The latter can occur in soft water lakes and may be examined by the 14C measurement of aqueous plants or the carbon dissolved and suspended in the water column. Some plants assimilate CO2 from the sediment. Their 14C activity is then dependent on the sediment accumulation rate and nutrients stored in the root system may also contribute misleading results. If water is filtered through ultra-fine membranes and then treated chemically, several fractions can be isolated for dating. The present study shows that the 14C activity of such fractions varies widely but with the weighted mean indicating an overall deficiency. Even the water from a raised bog evidences a 14C deficiency relative to contemporary atmospheric CO2. Charcoal from an archaeologic site and peat from corresponding layers in a nearby bog have yielded significantly different ages. The fact that the Cladium peat was from a very calcareous area is significant. The risk of contamination by younger root material is also documented.
    • Radiocarbon in Particulate Matter from the Eastern Sub-Arctic Pacific Ocean: Evidence of a Source of Terrestrial Carbon to the Deep Sea

      Druffel, Ellen R. M.; Honjo, Susumu; Griffin, Sheila; Wong, C. S. (American Journal of Science, 1986-01-01)
      Carbon isotope ratios were measured in organic and inorganic carbon of settling particulate matter collected with a sediment trap at Ocean Station "P" in the Gulf of Alaska from March to October, 1983. Dissolved inorganic carbon (DIG) in surface sea water collected during two different seasons in 1984 were analyzed using large gas proportional counters and revealed a minimum seasonal Delta-14C variation of 14 per mil. Results show that the 14C of calcium carbonate sedimenting to the deep sea is the same as that measured in surface water DIG. In contrast, particulate organic carbon (POC) had significantly higher Delta-14C values (by 25-70 per mil) than that in surface water DIG. Also, the delta-13C of the POC was markedly lower than previously reported values from other trap stations and marine particulate matter in general. Results from this study suggest that a significant amount of the POC settling to the deep sea at this pelagic station is of terrestrial origin, not strictly of marine origin as had previously been believed.
    • Uptake of Anthropogenic CO2 by Lateral Transport Models of the Ocean Based on the Distribution of Bomb-Produced 14C

      Peng, Tsung Hung (American Journal of Science, 1986-01-01)
      The pattern of global water column inventories of bomb-produced 14C suggests that a sizeable portion of bomb 14C that entered the Antarctic, northern Pacific, and tropical oceans has been transported to adjacent temperate regions. Models of lateral transport of surface water in the Atlantic, Indian, and Pacific Oceans are based on this distribution pattern. Upwelling of bomb-14C-free water from below takes place in the Antarctic, northern Pacific, and tropical regions; downwelling of surface water occurs in the temperate oceans and northern Atlantic. Uptake of excess CO2 by these models is calculated using the observed Mauna Loa pCO2 record as an input function. Results indicate that 35% of fossil fuel CO2 is taken up by these model oceans during the period 1.958-1980. Considering the observed airborne fraction of 0.55, it appears that ca 10% of the global fossil fuel CO2 is still missing.
    • Establishment of a Working Data Base for the International Exchange of 14C Data Using Universal Transfer Formats

      Wilcock, J. D.; Otlet, R. L.; Walker, A. J.; Charlesworth, S. A.; Drodge, J. (American Journal of Science, 1986-01-01)
      A high-level record structure for the international communication of 14C data bases is proposed. The record structure is based on the high-level communication format first proposed by the authors at the 23rd International Symposium on Archaeometry, Naples, 1983 and does not require the abandonment of existing systems. A description is given of an implementation of the high-level system at Harwell, with examples of retrieval in an international format (the Radiocarbon date list format) and a keyword-organized local format.
    • The AMS Dating of Separate Fractions in Archaeology

      Batten, R. J.; Gillespie, Richard; Gowlett, J. A. J.; Hedges, Robert E. M. (American Journal of Science, 1986-01-01)
    • The Chemical Preparation of AgCl for Measuring 36Cl in Polar Ice with Accelerator Mass Spectrometry

      Conard, N. J.; Elmore, David; Kubik, P. W.; Gove, H. E.; Tubbs, L. E.; Chrunyk, B. A.; Wahlen, Martin (American Journal of Science, 1986-01-01)
      A method of chemical separation and purification of chloride from relatively small samples (500 to 2100g) of glacial ice is presented. With this procedure the first successful measurements of pre-bomb levels of 36Cl in Greenland ice have been made. Emphasis is placed on methods of reducing sulfur, which causes interference in the accelerator mass spectrometry, and in maximizing the yield. Data regarding the selection of materials for sample holders and the use of metal powders for extending the lifetime of the sample are also presented.
    • The Power of 14C Measurements Combined with Chemical Characterization for Tracing Urban Aerosol in Norway

      Currie, L. A.; Klouda, G. A.; Schjoldager, Jorgen; Ramdahl, Thomas (American Journal of Science, 1986-01-01)
      Changing fuel patterns and increased awareness of health effects from combustion aerosols have generated considerable interest in the use of 14C as a biogenic-fossil aerosol source discriminator. Prior studies in the US demonstrated the importance of 14C measurement for estimating the wood-burning contribution to urban aerosols. The present work treats a specific air-pollution problem in the town of Elverum, Norway where large wintertime concentrations of aerosol carbon and polycyclic aromatic hydrocarbons (PAH) were suspected to come from residential woodl combustion (RWC). The problem was significant in that up to 50 micrograms/m3[C] and 490 micrograms/m3[PAH] were found during pollution episodes. Samples collected during two winters were analyzed for C, C, PAH, and several elements in the fine fraction (<3 micrometers) aerosol. Source apportionment based on these species indicated an average of ca 65% RWC-carbon (14C), ca 5% fine particle mass from motor vehicles (Pb), but negligible contributions from heavy fuel oil (Ni, V). Patterns of 14C and total C, examined as a function of temperature and PAH, indicated large increases in RWC aerosol on the coldest days, and a major RWC contribution to the PAH fraction. Patterns with inorganic species implied multiple tracer sources, and one important case of long-range transport.