• Nancy Natural Radiocarbon Measurements I

      Coppens, R.; Durand, G. L. A.; Guillet, B. (American Journal of Science, 1968-01-01)
    • Nancy Natural Radiocarbon Measurements II

      Hassko, B.; Guillet, B.; Coppens, R. (American Journal of Science, 1969-01-01)
    • Nancy Natural Radiocarbon Measurements III

      Hassko, B.; Guillet, B.; Jaegy, R.; Coppens, R. (American Journal of Science, 1974-01-01)
    • Nancy Natural Radiocarbon Measurements IV

      Richard, P.; Guillet, B.; Jaegy, R.; Coppens, R. (American Journal of Science, 1978-01-01)
    • Nancy Natural Radiocarbon Measurements V

      Coppens, R.; Guillet, B.; Jaegy, R.; Richard, P. (American Journal of Science, 1979-01-01)
    • Nancy Natural Radiocarbon Measurements VI

      Coppens, René; Guillet, Bernhard; Jaegy, Robert; Richard, Pierre (American Journal of Science, 1980-01-01)
    • National Physical Laboratory Radiocarbon Measurements I

      Callow, W. J.; Baker, M. J.; Pritchard, D. H. (American Journal of Science, 1963-01-01)
    • National Physical Laboratory Radiocarbon Measurements II

      Callow, W. J.; Baker, M. J.; Pritchard, Daphne H. (American Journal of Science, 1964-01-01)
    • National Physical Laboratory Radiocarbon Measurements III

      Callow, W. J.; Baker, M. J.; Hassall, Geraldine I. (American Journal of Science, 1965-01-01)
    • National Physical Laboratory Radiocarbon Measurements IV

      Callow, W. J.; Baker, M. J.; Hassall, Geraldine I. (American Journal of Science, 1966-01-01)
    • National Physical Laboratory Radiocarbon Measurements V

      Callow, W. J.; Hassall, Geraldine I. (American Journal of Science, 1968-01-01)
    • National Physical Laboratory Radiocarbon Measurements VI

      Callow, W. J.; Hassall, Geraldine I. (American Journal of Science, 1969-01-01)
    • National Physical Laboratory Radiocarbon Measurements VII

      Callow, W. J.; Hassall, Geraldine I. (American Journal of Science, 1969-12-31)
    • National Taiwan University Radiocarbon Dates III

      Liu, Tsung-Kwei (Department of Geosciences, The University of Arizona, 1994-01-01)
    • National Taiwan University Radiocarbon Measurements I

      Hsu, Yuin-Chi; Huang, Chia-Yi; Lu, Shih-Chong (American Journal of Science, 1969-12-31)
    • National Taiwan University Radiocarbon Measurements II

      Hsu, Yuin Chi; Chou, Muh-Chen; Hsu, Yi-Chuan; Lin, Song-Yun; Lu, Shih-Chong (American Journal of Science, 1973-01-01)
    • Natural Abundance of Carbon Isotopes (14C, 13C) in Lichens and Calcium Oxalate Pruina: Implications for Archaeological and Paleoenvironmental Studies

      Beazley, Melanie J.; Rickman, Richard D.; Ingram, Debra K.; Boutton, Thomas W.; Russ, Jon (Department of Geosciences, The University of Arizona, 2002-01-01)
      Radiocarbon ages of calcium oxalate that occurs naturally on rock surfaces have been used recently in archaeological and paleoenvironmental studies. Oxalate rock coatings are found globally, with most appearing to be residues from epilithic lichens. To explore the source(s) of carbon used by these organisms for the production of oxalate we measured the natural abundances of 14C and 13C in 5 oxalate-producing lichen species, 3 growing on limestone in southwestern Texas and 2 on sandstone in Arkansas. We also examined the distribution of the isotopes between the calcium oxalate and lichen tissues by separating these components and measuring the 13C/C independently. The results demonstrate that the limestone species were slightly enriched in 14C, by 1.7 per mil, relative to the sandstone species, which suggests that "dead" carbon from the limestone substrate does not constitute a significant source of carbon for the production of oxalate. The calcium oxalate produced by the lichens is also enriched in 13C by 6.5 per mil compared to the lichen tissues, demonstrating that there is a large carbon isotope discrimination during oxalate biosynthesis. These results support the reliability of 14C ages of calcium oxalate rock coatings used for archaeological and paleoclimate studies.
    • Natural Climate Variability During the Holocene

      Dergachev, V. A.; Raspopov, O. M.; Damblon, F.; Jungner, H.; Zaitseva, G. I. (Department of Geosciences, The University of Arizona, 2007-01-01)
      High-precision radiocarbon age calibration for different terrestrial samples allows us to establish accurate boundaries for many climatic time series. At the same time, the fluctuations of 14C content reflect solar variability. A bispectrum analysis of long-term series of the 14C content deduced from decadal measurements in tree rings demonstrates the existence of amplitude modulation, with a period of main modulation of ~2400 yr. In 14C time series for the last 11 kyr, major oscillations are distinguished at 8.5-7.8, 5.4-4.7, 2.6-2.2, and 1.1-0.4 cal kyr BP with ~2400-yr periodicity. High amplitudes in cosmogenic isotope content with a periodicity of about 2400 yr appear synchronous to cooling events documented in Greenland ice cores, to the timing of worldwide Holocene glacier expansion, and to the periods of lake-level changes. This paper focuses on revealing solar forcing on the Earths climate and about the nature, significance, and impact of sharp Holocene climate variability on human societies and civilizations.
    • Natural Processes and Time Fluctuations in the Radiocarbon Concentration of the Atmosphere

      Dergachev, V. E.; Kocharov, G. E. (American Journal of Science, 1980-01-01)
      The concentration of radiocarbon in the earth's atmosphere is used to analyze the complex of problems associated with the study of various astrophysical, geophysical, and geochemical phenomena within the framework of the All-Union problem of Astrophysical Phenomena and Radiocarbon. Effects of the supernovae explosions, solar activity, geomagnetic field and climatic changes in the 14C level in tree-rings are considered.
    • Natural Radiocarbon Measurements in Brazilian Soils Developed on Basic Rocks

      Pessenda, L. C. R.; Valencia, E. P. E.; Camargo, P. B.; Telles, E. C. C.; Martinelli, L. A.; Cerri, C. C.; Aravena, Ramon; Rozanski, Kazimierz (Department of Geosciences, The University of Arizona, 1996-01-01)
      This paper presents 14C, 13C and chemical data of soil organic matter (SOM) in three soil profiles under native forests from Brazil: Londrina (southern), Piracicaba (southeastern) and Altamira (northern). The main objective is to use carbon isotopes in tropical and subtropical soils of Brazil to provide information about vegetation changes that occurred in relation to climate changes during the Holocene. 14C data from SOM indicate that the organic matter in the soils studied is of at least Holocene age. 13C data indicate that C4 plants probably provided the dominant vegetation in Londrina and Piracicaba during the early and mid-Holocene and that C3 plants provided the dominant vegetation in the Altamira region during the Holocene.