• Microchemical and Molecular Dating

      Currie, L. A.; Stafford, T. W.; Sheffield, A. E.; Klouda, G. A.; Wise, S. A.; Fletcher, R. A.; Donahue, Douglas J.; Jull, A. J. Timothy; Linick, T. W. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The depth and reliability of archaeological and environmental information on ages, sources and pathways of carbon are being greatly enhanced through a new synergism between advances in "micro 14C dating" and advances in micro-organic analytical chemistry and individual particle characterization. Recent activities at the National Institute of Standards and Technology (NIST, formerly NBS) involving this linkage include dating individual amino acids isolated from bone collagen and the apportionment or tracing of individual carbon compounds derived from anthropogenic sources. Important knowledge has been gained through "direct" (sequential) and "indirect" (parallel) links between microchemistry and 14C measurement. The former is illustrated by 14C measurements on specific amino acids and on the polycyclic aromatic hydrocarbon (PAH) class of compounds. Isolation of the respective molecular fractions from far greater quantities of extraneous carbon held the key to valid dating and source apportionment respectively. Parallel data on 14C and molecular patterns promises new knowledge about the identity of sources of environmental carbon at the nanogram level through multivariate techniques such as principal component analysis and multiple linear regression. Examples are given for atmospheric particulate carbon, using PAM molecular patterns and laser microprobe mass spectral patterns.
    • Non-Age-Related Variations in Aspartic Acid Racemization in Bone from a Radiocarbon-Dated Late Holocene Archaeological Site

      Taylor, R. E.; Ennis, P. J.; Slota, Peter; Payen, L. A. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Wide variations in D/Lasp values are exhibited in a series of bone samples of assumed similar age associated with a suite of 14C determinations from stratified contexts in a late Holocene archaeological site. In this group of bone samples, major differences in D/Lasp ratios appear to be correlated primarily with variability in amino acid nitrogen content and GlY/Glu ratios.
    • Optimization of Liquid Scintillation Counting Conditions with Two Kinds of Vials and Detector Shields for Low-Activity Radiocarbon Measurements

      Rauret, Gemma A.; Mestres, J. S.; Garcia, J. F. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Low-level radiocarbon measurements were made using two liquid scintillation (LS) counters, both with passive lead shields of approximately the same dimensions. The first one had a conventional background reduction with low-activity lead and "high-low" coincidence bias selection, and the second one had a spectrum analysis background reduction based on the different three-dimensional pulse-height signal of background and beta pulses. The performance of commercial teflon-copper and glass vials were compared with both LS counters. Optimum counting conditions for the two detectors studied were also established. From results obtained, quality parameters and characteristics of quench curves were studied. Performances of each counter in the working conditions established were also compared.
    • Radiocarbon Chronology and Magnetic Susceptibility Variation in Kumaori Lakes Sediments

      Kusumgar, Sheela; Agrawal, D. P.; Sharma, Pankaj (Department of Geosciences, The University of Arizona, 1989-01-01)
      This study was carried out to determine time controls of erosion and sedimentation in the catchment area and lakes of the Naini Tal district in the Kumaon Himalayas. We present here our preliminary data from five lakes, Beon Tal, Garud Tal, Sukha Tal, Bhim Tal and Kamal Tal (Naukuchia Tal). A number of 14C dates are now available to estimate the sedimentation rate of the five lakes and magnetic susceptibility (xL ; xfd) variation to determine the signature of sediment source. High xfd values indicate a higher proportion of soil component generally characterized by a slower rate of deposition, and low xfd values with a higher rate of sedimentation indicate rock-debris-derived sediment. A 14C chronology enables us to estimate the mean sedimentation rate whereas rock magnetic properties help us to characterize the type of source responsible for sedimentation.
    • Radiocarbon Dating of Ostrich Eggshells

      Freundlich, Jürgen C.; Kuper, Rudolph; Breunig, Peter; Bertram, Hans-Georg (Department of Geosciences, The University of Arizona, 1989-01-01)
      Unlike wood charcoal, as found admixed to other cultural remains, ostrich eggshells can be of more direct significance in 14C dating, especially if they were processed to form, eg, eggshell beads. Normally the time span between laying the egg and working the shell beads is short enough to be negligible for 14C dating purposes. Another advantage of eggshell dating is that the carbonate of the shell seems to keep exceptionally well over the millennia, whereas, especially in surface sites in a desert environment, organic material such as wood, charcoal or bone protein tends to decompose. With few comparative test samples, we thought ostrich egg samples would yield 14C dates somewhat too young. The deviation is, however, balanced by performing 13C analyses and a correction for isotope fractionation of ca 350yr.
    • 41Ca Concentrations in Modern Bone and Their Implications for Dating

      Middleton, Roy; Fink, David; Klein, Jeffrey; Sharma, Pankaj (Department of Geosciences, The University of Arizona, 1989-01-01)
      We have made the first measurements without pre-enrichment of 41Ca in terrestrial rock and bone samples using accelerator mass spectrometry. Although the results in tufa deposits from Egypt are in good agreement with the saturation value of 8 x 10^-15 predicted by Raisbeck and Yiou (1979), the average 41Ca:40Ca ratio of 2x10^-15 (range: 0.6 to 4.2x10^-15) that we measure in modern bone is an order of magnitude lower than that obtained previously by Henning, et al (1987) on a cow bone that was measured using AMS following isotope enrichment. The low value and the variability (more than a factor of seven) of the 4 Ca:40Ca ratio in modern bone make the possibility of dating bones using 41Ca unlikely.
    • Radiocarbon Dating of Travertine Deposits, Arbuckle Mountains, Oklahoma

      Srdoč, Dušan; Chafetz, Henry; Utech, Nancy (Department of Geosciences, The University of Arizona, 1989-01-01)
      Travertine deposits occur abundantly at past and present sites of waterfalls in the Arbuckle Mountains region of Oklahoma. This area (1600km2) consists of folded and faulted Prepaleozoic and Paleozoic rocks, with abundant outcrops of Paleozoic carbonate rocks. Samples of recently deposited and old travertine from the Turner Falls area were collected during a 1987 field trip and analyzed for 13C, 14C and 18O content. The aquatic chemistry of travertine depositing creeks was investigated systematically and compared with those of similar areas in SE and central Europe.
    • A Beta Test Comparison Between the New Packard 2260 XL and the LKB Quantulus and 1219 SM: Low-Level Radiocarbon and Tritium Determinations

      Kalin, Robert M. (Department of Geosciences, The University of Arizona, 1989-01-01)
      A Packard 2260 XL liquid scintillation counter was placed in an underground counting chamber to test performance under immense physical shielding. Results from the Packard 2260 XL are compared with two other counters under the same conditions, the LKB Quantulus, which has operated for two years in this laboratory, and the LKB 1219 SM, in use since January 1988.
    • A 36Cl Profile in Greenland Ice from AD 1265 to 1865

      Conard, N. J.; Gove, H. E.; Elmore, David (Department of Geosciences, The University of Arizona, 1989-01-01)
      We have measured the concentration of 36Cl in 67 samples from the upper portion of the Camp Century ice core. The profile extends from AD 1265 to 1865 and covers the times of the Wolf (AD 1282-1342), Spoerer (AD 1416-1534) and Maunder (AD 1645-1715) minima in sunspot number. Although the profile exhibits much short-term variation, a smoothed plot of the data shows a strong peak in 36Cl concentration over the time of the Maunder Minimum. The deeper part of the core suggests increased deposition of 36Cl over the periods of the Wolf and Spoerer minima. The time resolution of the profile is inadequate for testing for an 11-year periodicity in our data. The data augment evidence from 10Be and 14C studies which indicate solar modulation of radioisotope production. Since, however, much of the short-term variation of 36Cl seems to be independent of solar activity, other factors must affect the deposition of 36Cl in ice. These variations could be due in part to mechanisms affecting the transport of 36Cl in the atmosphere. Based on our data from Camp Century, we calculate an average input of 36Cl of 24 atoms/m2 sec.
    • A Comparison of Methods Used for the Calibration of Radiocarbon Dates

      Aitchison, T. C.; Leese, Morven; Michczynska, Danuta J.; Mook, W. G.; Otlet, R. L.; Ottaway, B. S.; Pazdur, Mieczysław F.; van der Plicht, Johannes; Reimer, P. J.; Robinson, S. W.; et al. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Current calibration methods for single and replicate 14C dates are compared. Various forms of tabular and graphic output are discussed. Results from all the methods show reasonable agreement but further methodological development and improvements in computer output are required. Comparison of existing techniques for a series of non-contemporaneous dates showed less agreement amongst participants on this issue. We recommend that calibrated dates should be presented as a combination of graphs and ranges, in preference to mean and standard deviation.
    • A Critical Review of Radiocarbon Dating of a Norse Settlement at L'Anse Aux Meadows, Newfoundland, Canada

      Nydal, Reidar (Department of Geosciences, The University of Arizona, 1989-01-01)
      Recent progress in high-precision calibrations of radiocarbon dates has led to evaluations of earlier research. This has been the case with dates from the Norse settlement at L'Anse aux Meadows which was discovered by Helge Ingstad in 1960. The most problematic feature of this series up to now was the use of sample material which partly derived from driftwood. The present paper concludes that charcoalfrom this site demonstrated no greater errors than normal from other settlement sites. With an assumed total systematic error of 30 +/- 20 years, as a mean for various tree rings, the calibrated age range of L'Anse aux Meadows is AD 975 -1020. This agrees well with the assumed historical age of ca AD 1000, a result which has also been recently corroborated by high-precision accelerator dating at the University of Toronto.
    • A Counter System for High-Precision 14C Dating

      Hertelendi, Ede; Csongor, Éva; Zaborszky, Laszlo; Molnar, Jozef; Gal, Janos; Györffi, Miklos; Nagy, Sandor (Department of Geosciences, The University of Arizona, 1989-01-01)
      A multicounter radiocarbon dating system was developed applying the experiences of the previous one-channel low-level counting facility. The counter system consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35-0.7dm3 and filled with either methane at high pressure (6 bar) or CO2 at 1 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples using high-pressure methane-filled counters (B is approximately equal to 0.7 cpm, S is approximately equal to 14 cpm) is better than 4 per mil after a counting period of seven days.
    • Recent 14C Activity in the Atmosphere, 14Clean Air" and Chernobyl Effect

      Olsson, Ingrid U. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Although the Chernobyl accident caused increased 14C levels in certain areas, it has been difficult to prove that it had any effect in two areas of Sweden and one on Svalbard (Spitsbergen), where the precipitation and wind conditions were such that the y-active fall-out was negligible. Knowledge of the steady regional decrease and annual variations at high latitudes, where the pollution from fossil fuel is less than in central Europe, is essential for global studies of the CO2 cycle. The present 14C excess is a net effect of the 14C supply, mainly from tests of nuclear weapons, and dilution, by 14C-free, fossil-fuel consumption. In Sweden, at these northern latitudes, the 14C excess is steadily slightly higher than for "clean air" in central Europe. Annual variations are also smaller in Sweden and Svalbard than in central Europe. The normal 14C excess on Svalbard is slightly less than in Sweden. Detailed results, especially from autumn 1984 to autumn 1987, are given for atmospheric CO2 collected in northern Sweden (Abisko) and on Svalbard (Kapp Linne) and for some atmospheric samples and plant material collected ca 50km east of Uppsala, very close to heavily polluted areas.
    • Complementary Use of Amino-Acid Epimerization and Radiocarbon Analysis for Dating of Mixed-Age Fossil Assemblages

      Goodfriend, Glenn A. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Several approaches to dealing with the problem of mixed-age fossil assemblages are presented. These involve the use of amino-acid epimerization analysis (D-alloisoleucine/L-isoleucine ratio, or A/I) and are illustrated by deposits of land snail shells. This method requires only very small samples, so shells can be analyzed individually. Mixed-age deposits are indicated when variation in A/I among individual shells within the deposit exceeds the analytical error. Methods are presented for 1) estimating the true time of deposition of slightly-mixed-age assemblages based on bulk 14C dates and epimer analyses, 2) selection (for 14C analysis) of a set of individual shells that are uniform in age and represent the true time of deposition, and 3) estimating ages of individual shells within a mixed-age deposit based on their A/I ratios.
    • The Influence of Afforestation on Upland Soils: The Use of "Bomb 14C" Enrichment as a Quantitative Tracer for Changes in Organic Status

      Harkness, D. D.; Harrison, A. F. (Department of Geosciences, The University of Arizona, 1989-01-01)
      A series of soil samples were collected in November 1984 from five stands of Sitka spruce planted at recorded times between 1951 and 1968. Within a comprehensive program of ecologic and biogeochemical analyses, natural 14C measurements on selected organic components of the 0 to 5cm soil horizons serve to quantify progressive changes induced in the organic carbon inventory and relative to that of the original grassland. Points of particular interest are: 1) an enhanced input of fresh organic matter in the years immediately following planting; this, in parallel with a net decrease in the total carbon content of the topsoil; 2) this freshly introduced carbon predominates in the soil profile even after 30 years of afforestation; 3) during the 15to 30-year growth period, the soil carbon content remains constant but progressive changes occur in its biogeochemical composition and rate of turnover.
    • The Need for a Calibrated Radiocarbon Chronology of Near East Archaeology

      Bruins, H. J.; Mook, W. G. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Progress in radiocarbon dating and calibration accuracy should lead to the development of a calibrated radiocarbon chronology of Near Eastern archaeology, particulary for historical times. The lack of such an independent and impartial chronology is a major constraint, not only in archaeological studies, but also for interdisciplinary research involving the history of man, landscape and climate in the Near East and adjacent regions.
    • The Timing of the Post-Glacial Marine Invasion of Kau Bay, Halmahara, Indonesia

      Barmawidjaja, D. M.; De Jong, A. F. M.; van der Borg, Klaas; Van der Kaars, W. A.; Van der Linden, W. J. M.; Zachariasse, W. J. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Kau Bay, Halmahera, Indonesia is a small marine basin that is separated from the adjacent SW Pacific Ocean by a shallow sill, 40m deep. Radiocarbon dating on piston cores in combination with a study on microfossils demonstrate that Kau Bay was a freshwater lake in Weichselian times. At 10,000 BP, the Bay became reconnected with the open ocean. If sill depth did not change in the intervening years, sea level at 10,000 BP stood 40m below the present level.
    • Downward Movement of Soil Organic Matter and Its Influence on Trace-Element Transport (210Pb, 137Cs) in the Soil

      Dörr, Helmut; Münnich, K. O. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Data on depth distribution and 14C content of soil organic carbon, and on soil CO2 production in forest ecosystems are presented and discussed. Downward movement and turnover of soil organic matter is estimated from a box chain model. The downward transfer velocity of soil organic material depends on the litter material composition and on the annual rate of microbial decomposition. Depth distribution of 210Pb and 137Cs was measured. The identical transfer velocity of 210Pb and soil organic material suggests that lead transport is due to movement of the organic material itself. Lead in organic-rich soils obviously is bound rather tightly to the organic carrier by ion exchange or organic complexing. 137Cs migration depends on the turnover and downward movement of soil organic material. Results suggest that cesium is not transported only by the downward movement of solid organic matter, but, due to chemical exchange between the organic and hydrous phases, travels faster than organic matter.
    • The Radiocarbon Data Base of Japan

      Omoto, Kunio (Department of Geosciences, The University of Arizona, 1989-01-01)
      About ten radiocarbon laboratories operate in Japan and have dated more than 25,000 samples since 1960. Geomorphic development and human activities since the last glaciation have been documented with radiocarbon determinations. In order to apply these dates more effectively, the author finds it necessary to create and maintain a radiocarbon database system, which he has been doing since 1985, using a personal computer system linked to a telephone line. A researcher may access, search and retrieve data from the Radiocarbon Database System of Japan.
    • The Radiocarbon Data Base at Rudjer Bošković Institute Radiocarbon Laboratory

      Obelić, Bogomil (Department of Geosciences, The University of Arizona, 1989-01-01)
      A multidisciplinary radiocarbon data base system written in dBASE III PLUS which follows the recommendations of the International Database Commission and specific requirements of our laboratory is described. The system updates, stores and maintains records and retrieves data according to specific key-words.