• 10 Steps to Evaluate Rangeland Riparian Health

      Fleming, William; Galt, Dee; Holechek, Jerry (Society for Range Management, 2001-12-01)
    • 10Be Analyses with a Compact AMS Facility—Are BeF2 Samples the Solution?

      Wacker, L.; Grajcar, M.; Ivy-Ochs, S.; Kubik, PW; Suter, M. (Department of Geosciences, The University of Arizona, 2004-01-01)
      The injection of 10BeFinstead of10BeOinto a compact accelerator mass spectrometry system with a terminal voltage of 0.58 MV was investigated, because BFmolecules are unstable and isobaric interference of 10B with 10Be can thus be significantly reduced. We describe the method we developed to prepare BeF2samples. 10Be was measured in a segmented gas ionization detector. Separation of 10Be from 10B could be achieved both for ions in the 1+ charge state with an energy of 0.8 MeV and in the 2+ charge state with an energy of 1.4 MeV. The 2+ ions are better separated, whereas the 1+ charge state has a higher transmission. 10Be/9Be ratios (approximately 10^-12) in a suite of rock samples were successfully determined for exposure dating in either charge state and compared with measurements made on the 6MV tandem.
    • 10Be, 14C Distribution, and Soil Production Rate in a Soil Profile of a Grassland Slope at Heshan Hilly Land, Guangdong

      Shen, C. D.; Beer, J.; Ivy-Ochs, S.; Sun, Y.; Yi, W.; Kubik, P. W.; Suter, M.; Li, Z.; Peng, S.; Yang, Y. (Department of Geosciences, The University of Arizona, 2004-01-01)
      Concentrations of organic carbon, carbon isotopes (13C and 14C), atmospheric 10Be in soil, and in situ 10Be in bedrock and weathering rock were determined in a study of a profile of a grassland slope at the Heshan Hilly Land Interdisciplinary Experimental Station, Chinese Academy of Sciences, in Guangdong Province, China. A good linear relationship between depth and the 14C apparent age of the organic carbon demonstrates that the rock weathering process and the accumulation process of organic matter in the slope are relatively stable. Both 14C and 10Be results show that about 34% of soil in the grassland slope has been eroded during the past 3800 yr. The 10Be results for interstitial soil from weathered rocks show that the 90-cm-thick weathering rock layer above the bedrock has evolved over a period of 1.36 Myr. The concentrations of in situ 10Be in the weathered rock and bedrock are 10.7 X 10^4 atoms/g and 8.31 X 10^-4 atoms/g, respectively. The weathering rate of the bedrock, equivalent to the soil production rate, was estimated at 8.8 X 10^-4 cm/yr, and the exposure ages of the weathered rock and the bedrock were 72 kyr and 230 kyr, respectively.
    • 10th Town Hall Probes Problems Of Agriculture

      College of Agriculture, University of Arizona (Tucson, AZ), 1967
    • 11 Fruitful years of Student Involvement

      Myers, Harold E.; College of Agriculture (College of Agriculture, University of Arizona (Tucson, AZ), 1969)
    • 12 Years of Sprinkler Irrigation Research

      Frost, K. R.; Agricultural Experiment Station (College of Agriculture, University of Arizona (Tucson, AZ), 1963)
    • 120º and Harvesting

      Littlefield, Joanne (College of Agriculture, University of Arizona (Tucson, AZ), 2007)
    • 13C Variation in Limestone on an Aquifer-Wide Scale and Its Effects on Groundwater 14C Dating Models

      Muller, A. B.; Mayo, A. L. (American Journal of Science, 1986-01-01)
      In modeling the initial 14C activity of ground waters, the delta-13C of marine limestone is taken conventionally to vary little about 0 per mil PDB. This variation was found to be 6.28 per mil in samples taken over intervals from 10^-2 to 1^5 meters in the Mooney Falls Member of the Redwall Limestone in northern Arizona. Such a variation will cause appreciable variability in the results of all four initial activity models tested. The variability, due primarily to a numerical instability in the models dependent on this parameter, can introduce significant uncertainty into groundwater "age" calculations.
    • 13CO2 and 14CO2 Measurements on Soil Atmosphere Sampled in the Western Great Plains of the US

      Haas, Herbert; Fisher, D. W.; Thorstenson, D. C.; Weeks, E. P. (American Journal of Science, 1983-01-01)
      Soil gas samples were obtained from the unsaturated zone at eight sites in the Great Plains. Three of these sites were sampled extensively for gas composition and carbon isotopes. Sampling equipment consisted of a nest of gas probes vertically spaced by roughly 3m at most sites, generally approaching the water table. Water wells, 10cm in diameter, were screened in the topmost layer groundwater. Inverted cattle tanks were used to collect CO2 samples from the soil surface. The major gas components were analyzed with emphasis on CO2, Delta--13C, and 14C measurements. The same components were studied in groundwater samples. Higher than atmospheric CO2 concentrations were found in all soil samples. Root respiration and oxidation of organic matter were sources for the additional CO2. When lignite was present in the unsaturated zone, gaseous oxygen reacted almost completely, and CO2 levels rose to 19%. Near the surface, annual cycles in total CO2, Delta--13C, and 14C were observed. 14C activities were close to present post-bomb levels at the surface and generally declined with depth. At some sites, oxidation of lignite caused decline of 14C levels to 1 or 2% of their surface value at 8m depth. Without lignite, the 14C activity remained above 50% at all depths. Concentrations of total carbon and its isotopes in ground water remained very stable throughout the study. This implies that geochemical processes in the aquifer vary on time scales longer than the seasonal effects observed in the near-surface unsaturated zone.
    • 13th International Radiocarbon Conference

      American Journal of Science, 1988-01-01
    • 13th International Radiocarbon Conference

      American Journal of Science, 1988-01-01
    • 14 Years of Rabbitbrush Control in Central Oregon

      Mohan, J. M. (Society for Range Management, 1973-11-01)
      Fourteen years (1956 to 1970) of chemical control for rubber and green rabbitbrush using the ester forms of 2,4-D produced consistent control, ranging from 85 to 98% on rubber rabbitbrush. The amount of new twig growth, soil moisture, rate and methods of application, total seasonal twig growth, and subsequent drought conditions proved critical for effective kills. Selective kills were achieved by manipulation of these factors. Site potential and response to changes that result from chemical control must be recognized. "Drainage Effect" is a complex of thermal drafts, topography, and soil differences that can adversely influence the percentage of rabbitbrush control achieved.
    • 14- Vs. 42-Paddock Rotational Grazing: Aboveground Biomass Dynamics, Forage Production, and Harvest Efficiency

      Heitschmidt, R. K.; Dowhower, S. L.; Walker, J. W. (Society for Range Management, 1987-05-01)
      Research was initiated at the Texas Experimental Ranch in 1981 to quantify the effects of 2 stocking densities, equivalent to 14- and 42-paddock rotational grazing (RG) treatments, on aboveground biomass dynamics, aboveground net primary production (ANPP), and harvest efficiency of forage. Baseline data were collected in 1981 from 3 adjacent 30-ha paddocks in a 14-paddock, cell designed RG treatment. Near the beginning of the 1982 growing season the center paddock was subdivided into three, 10-ha paddocks to establish the RG-42 treatment. Stocking densities in the 14- and 42-paddock treatments were 4.2 and 12.5 AU/ha, respectively, from March 1982 to June 1984 and 3.0 and 9.1 AU/ha from June to November 1984. During 1981, estimated ANPP in the two RG-14 paddocks averaged 4,088 kg/ha as compared to 5,762 in the single RG-42 paddock. Following subdivision, ANPP in the RG-14 paddocks averaged 2,533 kg/ha as compared to 2,670 kg/ha in the RG-42 paddocks. Although ANPP varied significantly among the 4 years of the study it was not affected by density treatment. Likewise, harvest efficiency varied among years but was unaffected by density treatment. Average harvest efficiency over the 4 years was about 42%. Aboveground biomass dynamics were also generally unaffected by density treatments.
    • 14- Vs. 42-Paddock Rotational Grazing: Forage Quality

      Heitschmidt, R. K.; Dowhower, S. L.; Walker, J. W. (Society for Range Management, 1987-07-01)
      Research was initiated at the Texas Experimental Ranch in 1981 to quantify the effects of 2 livestock densities on forage quality in a rotational grazing (RG) treatment. Livestock densities evaluated were equivalent to 14 and 42-paddock RG treatments. Baseline data were collected in 1981 from 3 adjacent 30-ha paddocks in a 465-ha, 14-paddock, cell designed RG treatment stocked at a rate of 3.6 ha/cow/year. Near the beginning of the 1982 growing season the center paddock was subdivided into three, 10-ha paddocks to establish the RG-42 treatment. Herbage standing crop was harvested before and after each grazing event during the 40-month period, separated by species or species group into live and dead tissue, and each fraction analyzed for percentage crude protein (CP) and organic matter digestibility (OMD). Livestock density had minimial effect on forage quality. Live tissue was of higher quality than senesced tissue regardless of plant species. Increases and decreases in overall quality during grazing periods were positively associated with rates of plant growth. Number of periods when forage quality increased or decreased during grazing and magnitude of change were unaffected by treatment. Lack of significant treatment effects on forage quality is attributed to the general absence of significant treatment effects on forage production, species composition, and live/dead ratios.
    • 14C Absolute Chronology of Pyramid III and the Dynastic Model at Pachacamac, Peru

      Michczyński, Adam; Eeckhout, Peter; Pazdur, Anna (Department of Geosciences, The University of Arizona, 2003-01-01)
      Pachacamac, covering an area of about 600 hectares (ha) near the Pacific shore, is one of the largest and most important archaeological sites in Peru. Most of the monumental adobe-made buildings of the later pre-Inca period (or Late Intermediate Period, about 10th-15th century AD) are so-called pyramids with ramps (the role of the ramps has been interpreted in different ways). Precise dating of the pyramids appears as a crucial step in defining the functions of Pachacamac in pre-Inca times. In this paper, we present the results obtained from 3 field campaigns at Pyramid III, one of the biggest buildings of the site. A total of 24 radiocarbon datasets from 4 different laboratories will help us to place the various steps of development of Pyramid III on a timescale, defined on the basis of the excavations. More absolute dates are available from another pyramid with ramps, which allow us to make comparisons and propose a new model of interpretation for the Pachacamac site during the Late Intermediate Period (LIP).
    • 14C Activity in Different Sections and Chemical Fractions of Oak Tree Rings, AD 1938-1981

      Olsson, I. U.; Possnert, Göran (Department of Geosciences, The University of Arizona, 1992-01-01)
      The 14C activity in rings from an oak tree grown in a suburb of Uppsala, Sweden has been studied for the period, AD 1938 to 1981. We compare the results with the atmospheric carbon dioxide records from Abisko, northern Sweden, where local or regional contamination from fossil-fuel combustion can be disregarded. We assess the influence from different chemical pretreatment procedures in use and compare HCl-NaOH-HCl treatment with cellulose extraction. We split each ring into two samples corresponding to early (spring) and late wood. A more refined partitioning has been applied to the years 1963 and 1964.
    • 14C Age Corrections in Antarctic Lake Sediments Inferred from Geochemistry

      Zale, Rolf (Department of Geosciences, The University of Arizona, 1994-01-01)
      Sediment from Lake Boeckella, Antarctic Peninsula, is richer in Ca, Cd, Cu, P, Sr and Zn than that of six other lakes in the area. The elements originate from Adélie penguin (Pygoscelis adeliae) guano on the lake shores. Changing Cu and P concentrations in the lake sediment are used as a proxy for penguin influence on the lake sediment from ca. 5850 BP to Present. A 14C dating model suggests that the 14C correction factor in the lake sediments depends on the penguin proxy, the apparent age of the penguin guano and the amount of particulate carbon originating from the carbon-bearing shales in the watershed. Glacial meltwater and dissolved carbonates do not contain enough "old" carbon to contribute significantly to the correction factor. Ages corrected with the 14C dating model agree with the depth vs. age curve based on independently 14C-dated tephra horizons. The reservoir effect has been constant since at least 5800 BP, implying long-term stability of the currents and water masses in the area. The existing chronology for Lake Boeckella has been recalculated. The period of glacial advance, previously thought to have culminated at 5000 BP, is now thought to have culminated at 4700 BP; deglaciatlon of the area is thought to have occurred at 6300 BP instead of 8680 BP.
    • 14C Age Measurements of Single-Year Tree Rings of Old Wood Samples 22,000 14C Years BP

      Sato, Taiichi; Sakurai, Hirohisa; Suzuki, Kayo; Takahashi, Yui (Department of Geosciences, The University of Arizona, 2010-01-01)
      Radiocarbon ages of single-year tree rings were measured for Kaminoyama wood samples using accelerator mass spectrometry (AMS) in 2 Japanese facilities, MALT and JAEA, in order to investigate the periodic variation of 14C concentrations relating to the 11-yr solar cycle near 26,000 yr BP. Eight sequential measurements of 14C ages were carried out for a set of 13 alternate single-year tree rings covering 26 yr. Averages of the 5 data sets in MALT and 3 data sets in JAEA were 22,146 +/- 50 and 22,407 +/- 58 14C yr BP, respectively, indicating an offset of 260 +/- 77 14C yr. Multiple sequential measurements are advantageous for evaluating offsets. The standard deviation of the residuals of 14C ages from the averages in each data set was 118 14C yr, in contrast to that of 234 14C yr for the combined data sets due to an elimination effect in the offsets. The profiles of weighted mean values for the residuals of 14C ages showed similar enhancements with a width of ~12 yr for measurements in the 2 facilities. This indicates the reproducibility of the multiple sequential measurements. In the profile for the combined 8 data sets, the 14C enhancement was 73 +/- 36 14C yr from the average.
    • 14C Age of Glaciation in Estrecho de Magallanes–Bahía Inútil, Chile

      Heusser, C. J. (Department of Geosciences, The University of Arizona, 1999-01-01)
      Basal 14C dates from a core of the mire at Puerto del Hambre (53 degrees 36'21"S, 70 degrees 55'53"W), located within the area of glaciation in Estrecho de Magallanes-Bahia Inutil, Chile, are no older than 14,455 +/115 yr BP. The 14C dates are on samples from which screening isolated autochthonous plant remains. Previous 14C dates of 15,800 +/200, 16,590 +/320, and 16,290 +/140 yr BP are from bulk samples collected from similar basal increments at the site during 3 separate, independent coring operations. The previous suite of 14C dates was suspected to be contaminated by older carbon in the light of chronological evidence, which indicates a 14C age of approximately 14,850 yr BP for glaciation elsewhere in southern Chile. Contamination by "infinitely old" carbon reworked from nearby Tertiary beds and redeposited at Puerto del Hambre is evidently the cause for the older 14C dates.
    • 14C Ages and Magnetic Stratigraphy in Three Australian Maars

      Barton, C. E.; Potach, H. A. (American Journal of Science, 1980-01-01)
      Detailed radiocarbon chronologies from three volcanic crater lakes (maars) in southeast Australia are examined in relationship to the magnetic mineral stratigraphies within lakes, and the magnetic secular variation stratigraphy between lakes. Some implications for magnetic dating are considered.