Now showing items 41-53 of 53

    • Hamburg Radiocarbon Thin Layer Soil Database

      Becker-Heidmann, Peter; Scharpenseel, Hans-Wilhelm; Wiechmann, Horst (Department of Geosciences, The University of Arizona, 1996-01-01)
      We report here the remainder of the Hamburg University dates on thin soil layers (HAM 1652-3129).
    • Geological Survey of Canada Soil Database

      McNeely, Roger (Department of Geosciences, The University of Arizona, 1996-01-01)
      The Geological Survey of Canada (GSC) has developed, over the past decade, a user-oriented database, Date Locator File, of Canadian samples dated by the 14C technique. This database presently contains >3500 soil and soil-related dates. The primary category in this suite of dates is peat, as a large portion of the Canadian landscape is covered with this type of organic soil. The data is available gratis to all researchers in a large variety of formats from simple lists to complex tables for inclusion in publications. The site localities can also be plotted on base maps suitable for publication. The database is actively augmented on an ongoing basis, but to continue to be relevant, it depends largely on the altruism of the scientific community.
    • Genotoxicity Study on Nicotine and Nicotine-Derived Nitrosamine by Accelerator Mass Spectrometry

      Li, X. S.; Wang, H. F.; Shi, J. Y.; Wang, X. Y.; Liu, Y. F.; Li, K.; Lu, X. Y.; Wang, J. J.; Liu, K. X.; Guo, Z. Y. (Department of Geosciences, The University of Arizona, 1996-01-01)
      We have studied DNA adduction with 14C-labe1ed nicotine and nicotine-derived nitrosamine, 4-(methylnitrosamino)1-(3-pyridyl)-1-butanone (NNK), by accelerator mass spectrometry (AMS) in mouse liver at doses equivalent to lowlevel exposure of humans. The dose ranges of nicotine and NNK administered were from 0.4g to 4.0x 10^2 micrograms kg b.w.-1, and from 0.1 micrograms to 2.0x10^4 micrograms kg b.w.-1, respectively. In the exposure of mice to either nicotine or NNK, the number of DNA adducts increased linearly with increasing dose. The detection limit of DNA adducts was 1 adduct per 1011 nucleotide molecules. This limit is 1-4 orders of magnitude lower than that of other techniques used for quantification of DNA adducts. The results of our animal experiments enabled us to speculate that nicotine is a potential carcinogen. According to the procedure for 14C-labeled-NNK synthesis, we discuss the ultimate chemical speciation of NNK bound to DNA. From the animal tests we derived a directly perceivable relation between tobacco consumption and DNA adduction as the carcinogenic risk assessment.
    • Further Application of Bomb 14C as a Tracer in the Atmosphere and Ocean

      NydaI, Reidar; Gislefoss, Jorunn S. (Department of Geosciences, The University of Arizona, 1996-01-01)
      Bomb 14C from nuclear tests in the atmosphere has proved to be a particularly useful tool in the study of the carbon cycle. We provide here a ca. 30-yr time series of 14C concentrations in the atmosphere between 28 degrees N and 71 degrees N and in the ocean surface between 45 degrees S and 45 degrees N. More recently (since 1990), a north-south profile also has been obtained for 14C in the surface waters of the Atlantic Ocean. The measurements were performed using the conventional technique of beta counting of large samples (4 to 5 liter CO2) in CO2 proportional counters. These data show that the 14C concentration in the atmosphere is leveling off with a time constant of 0.055 yr-1, and is now approaching that of the ocean surface at lower latitudes. Additional tracer studies have been concerned especially with the penetration of bomb 14C into the deep ocean. The Norwegian and Greenland seas are of interest as a sink for atmospheric CO2 and also a source of water for the deep Atlantic Ocean. During the last five years, several 14C depth profiles have been measured from the Fram Strait (79 degrees N) to south of Iceland (62 degrees N), using the AMS technique available at the University of Arizona AMS Facility. We considered it important to repeat and compare a few of the profiles with those produced by the GEOSECS expedition in 1972 and the TTO expedition in 1981. The profiles show that water descending to the deep Atlantic Ocean is originating mainly from intermediate and surface depths in the Nordic Seas. However, the ventilation rate of the Norwegian Sea deepwater is too slow to be an important component in the transfer of water over the Greenland-Scotland Ridge.
    • Estimation of Slow- and Fast-Cycling Soil Organic Carbon Pools from 6N HCl Hydrolysis

      Leavitt, S. W.; Follett, R. F.; Paul, E. A. (Department of Geosciences, The University of Arizona, 1996-01-01)
      Acid hydrolysis is used to fractionate the soil organic carbon pool into relatively slowand fast-cycling compartments on soils from Arizona, the Great Plains states and Michigan collected for carbon isotope tracer studies related to soil carbon sequestration, for studies of shifts in C3/C4 vegetation, and for "pre-bomb" soil-carbon inventories. Prior to hydrolysis, soil samples are first treated with cold 0.5-1N HCl to remove soil carbonates if necessary. Samples are then dispersed in a concentrated NaCI solution (p is roughly equal to 1.2 g cm-3) and floated plant fragments are skimmed off the surface. After rinsing and drying, all remaining recognizable plant fragments are picked from the soil under 20x magnification. Plant-free soils, and hot, 6N HCl acid-hydrolysis residue and hydrolyzate fractions are analyzed for carbon content, delta-13C and 14C age, and the carbon distribution is verified within 1-2% by stable-carbon isotope mass balance. On average, the recalcitrant residue fraction is 1800 yr older and 2.6 per mil more 13C-depleted than total soil organic carbon. A test of hydrolysis with fresh plant fragments produced as much as 71-76% in the acid-hydrolysis residue pool. Thus, if plant fragments are not largely removed prior to hydrolysis, the residue fraction may date much younger than it actually is.
    • Comparison of Fractionation Methods for Soil Organic Matter 14C Analysis

      Trumbore, Susan E.; Zheng, Shuhui (Department of Geosciences, The University of Arizona, 1996-01-01)
      14C measurements provide a useful test for determining the degree to which chemical and physical fractionation of soil organic matter (SOM) are successful in separating labile and refractory organic matter components. Results from AMS measurements of fractionated SOM made as part of several projects are summarized here, together with suggestions for standardization of fractionation procedures. Although no single fractionation method will unequivocally separate SOM into components cycling on annual, decadal and millennial time scales, a combination of physical (density separation or sieving) and chemical separation methods (combined acid and base hydrolysis) provides useful constraints for models of soil carbon dynamics in several soil types.
    • Book Review: Learning from Things: Method and Theory of Material Culture Studies, W. David Kingery (Ed.)

      Skibo, James M. (Department of Geosciences, The University of Arizona, 1996-01-01)
    • Author Index Volume 38, Nos. 2 and 3, 1996

      Department of Geosciences, The University of Arizona, 1996-01-01
    • An Archaeological and Paleontological Chronology for Daisy Cave (CA-SMI-261), San Miguel Island, California

      Erlandson, Jon M.; Kennett, Douglas J.; Ingram, B. Lynn; Guthrie, Daniel A.; Morris, Don P.; Tveskov, Mark A.; West, G. James; Walker, Phillip L. (Department of Geosciences, The University of Arizona, 1996-01-01)
      We provide detailed contextual information on 25 14C dates for unusually well-preserved archaeological and paleontological remains from Daisy Cave. Paleontological materials, including faunal and floral remains, have been recovered from deposits spanning roughly the past 16,000 yr, while archaeological materials date back to ca. 10,500 BP. Multidisciplinary investigations at the site provide a detailed record of environmental and cultural changes on San Miguel Island during this time period. This record includes evidence for the local or regional extinction of a number of animal species, as well as some of the earliest evidence for the human use of boats and other maritime activities in the Americas. Data from Daisy Cave contribute to a growing body of evidence that Paleoindians had adapted to a wide variety of New World environments prior to 10,000 BP. Analysis of shell-charcoal pairs, along with isotopic analysis of associated marine shells, supports the general validity of marine shell dating, but also provides evidence for temporal fluctuations in the reservoir effect within the Santa Barbara Channel region.
    • 14C Laboratories

      Department of Geosciences, The University of Arizona, 1996-01-01
    • 14C Measurements of Soil Organic Matter, Soil CO2 and Dissolved Organic Carbon (1987-1992)

      Tegen, Ina; Dörr, Helmut (Department of Geosciences, The University of Arizona, 1996-01-01)
      For several undisturbed sites in Germany, 14C data are reported for soil organic matter (SOM) (4 sites), soil CO2 (10 sites) and dissolved organic carbon (DOC) (1 site). With the assumption of a fast degradable component (lifetime ca. 1 yr) and a slow degradable component (lifetime ca. 100 yr), a range between 0.6 and 1.6 mm yr-1 has been determined for the downward migration rates of soil organic carbon at the sampling sites from the soil 14C data. The soil CO2 measurements show that in deciduous forests the fast degradable component is ca. 60% and the slow degradable component is ca. 40% of the SOM. In coniferous forests this ratio is reversed. The 14C results for DOC could not be explained with the assumption of a first-order decay process. The removal of soil organic carbon by DOC is of minor importance for the estimation of carbon budgets for the investigated site.
    • 14C Dating of an Israelite Biblical Site at Kuntillet Ajrud (Horvat Teman): Correction, Extension and Improved Age Estimate

      Carmi, Israel; Segal, Dror (Department of Geosciences, The University of Arizona, 1996-01-01)
    • 14C Dating and Soil Organic Matter Dynamics in Arctic and Subarctic Ecosystems

      Cherkinsky, A. E. (Department of Geosciences, The University of Arizona, 1996-01-01)
      The carbon content, pH and 14C concentration of humic acids were determined for three soil series of Arctic and Subarctic ecosystems. The measured 14C ages were interpreted in the light of an equilibrium model of humus formation and of mineralization processes in recent soils, and the coefficient of renovation, Kr, was calculated for humic acids. The comparison of Kr for series formed under different climatic conditions suggested that global warming could accelerate decomposition of soil organic matter and possibly increase productivity of ecosystems of the Arctic region.