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  Radiocarbon, Volume 38, Number 2 (1996)

  Department of Geosciences, The University of Arizona, 1996-01-01
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  To All My Friends

  Kra, Renee (Department of Geosciences, The University of Arizona, 1996-01-01)
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  Athol Rafter, 1913-1996

  Sparks, Rodger (Department of Geosciences, The University of Arizona, 1996-01-01)
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  1997 Price List

  Department of Geosciences, The University of Arizona, 1996-01-01
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  16th International Radiocarbon Conference

  Department of Geosciences, The University of Arizona, 1996-01-01
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  Using Bulk Soil Radiocarbon Measurements to Estimate Soil Organic Matter Turnover Times: Implications for Atmospheric CO2 Levels

  Harrison, Kevin G. (Department of Geosciences, The University of Arizona, 1996-01-01)

  Although soil contains about three times the amount of carbon present in the preindustrial atmosphere, determining how perturbations (e.g., changing land use, CO2 fertilization, changing climate and anthropogenic nitrogen deposition) alter soil carbon storage and influence atmospheric CO2 levels has proved elusive. Not knowing the soil carbon turnover times causes part of this uncertainty. I outline a strategy for using radiocarbon measurements to estimate soil organic matter turnover times and inventories in native soil. The resulting estimates of carbon exchange produce reasonable agreement with measurements of CO2 fluxes from soil. Furthermore, derivatives of the model are used to explore soil carbon dynamics of cultivated and recovering soil. Because the models can reproduce observed soil 14C measurements in native, cultivated, and recovering ecosystems (i.e., the underlying assumptions appear reasonable), the native model was modified to estimate the potential rate of additional carbon storage because of CO2 fertilization. This process may account for 45-65% of the "missing CO2 sink."
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  The Use of Carbon Isotopes (13C, 14C) in Soil to Evaluate Vegetation Changes During the Holocene in Central Brazil

  Pessenda, L. C. R.; Aravena, Ramon; Melfi, A. J.; Telles, E. C. C.; Boulet, René; Valencia, E. P. E.; Tomazello, Mario (Department of Geosciences, The University of Arizona, 1996-01-01)

  This paper presents carbon isotope data measured in three soil profiles from the Salitre area, Central Brazil. The study forms part of a research project on tropical and subtropical soils in Brazil, in which the main objective is to use carbon isotopes to provide information about vegetation changes that have occurred in relation to climate changes during the Holocene. 14C data from charcoal samples and soil organic matter (SOM) indicate that the organic matter in the soils studied is of Holocene age at least. Furthermore, the presence of a significant amount of charcoal in the soils suggests that forest fire was a significant ocurrence during the Holocene and probably had an important role in determining the dynamics of forest vegetation in the study area. Correspondingly, 13C data indicate that C3 plants provided the dominant vegetation of the study area, even during the dry periods when savanna vegetation is supposed to have replaced the forest communities. This study contributes to our better understanding of the relation between climatic changes and vegetation in the subtropical region of Brazil.
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  The Effect of Tillage on Soil Organic Matter Using 14C: A Case Study

  Rutberg, Randye L.; Schimel, David S.; Hajdas, Irena; Broecker, Wallace S. (Department of Geosciences, The University of Arizona, 1996-01-01)

  We compared four adjacent soil plots in an effort to determine the effect of land use on soil carbon storage. The plots were located at the High Plains Agricultural Research Laboratory near Sidney, Nebraska. We measured 14C, total carbon, total nitrogen and 137Ce to determine the size and turnover times of rapid and stable soil organic matter (SOM) pools, and their relation to land-use practices. Results were consistent with the model produced by Harrison, Broecker and Bonani (1993a) in that the 14C surface soil data fell on the time trend plots of world 14C surface soil data, indicating that the natural sod and non-tilled plots had a rapidly turning over SOM pool, comprising ca. 75% of surface soil carbon, and the tilled plots had a rapidly turning over SOM pool, comprising only 50% of surface soil carbon.
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  Requirements for an International Radiocarbon Soils Database

  Becker-Heidmann, Peter (Department of Geosciences, The University of Arizona, 1996-01-01)
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  Radiocarbon Dating of Soils: Database Contribution by Bonn and Hamburg

  Scharpenseel, H. W.; Pietig, Franz; Schiffman, Heinrich; Becker-Heidmann, Peter (Department of Geosciences, The University of Arizona, 1996-01-01)

  We present a compilation of 14C soil dates measured at the University of Hamburg through 1984 (HAM-1597).
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  Parameters of a Radiocarbon Installation

  Khait, Vladimir Z. (Department of Geosciences, The University of Arizona, 1996-01-01)

  I aim to define instrumental parameters of a radiocarbon laboratory installation whereby one can estimate its precision and a maximum age up to which its measuring results are reliable. The commonly accepted factor of merit (FM) relates the precision of measurement to Poisson statistics. Unlike the FM, the proposed parameters show the extent to which a 14C laboratory is affected by destabilizing factors that could cause additional measurement errors. Assuming that all destabilizing factors produce either a change in counting efficiency or additional fluctuations of the background counting rate, I have derived two parameters for consideration.
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  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.
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  Introduction: Challenges in the Soil

  Harkness, Doug (Department of Geosciences, The University of Arizona, 1996-01-01)
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  Historic Measurements of Radiocarbon in New Zealand Soils

  Lassey, K. R.; Tate, K. R.; Sparks, R. J.; Claydon, J. J. (Department of Geosciences, The University of Arizona, 1996-01-01)

  Extensive measurements of radiocarbon have been used in New Zealand since the mid-1960s to follow carbon (C) movement and turnover in soils. We present here unpublished radiocarbon (14C) measurements on a range of eight New Zealand soils with details of the sites, ecosystems, climates, soil descriptions and associated analytical data. An overview is also given of published 14C measurements on soils, and the use of these measurements to model soil C turnover.
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  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).
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  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.
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  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.
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  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.
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  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.
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  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.

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