Elder Kathryn L.

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Kathryn L.

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Now showing 1 - 8 of 8
  • Article
    Single Step Production of Graphite from Organic Samples [Poster]
    ( 2017) Elder, Kathryn L. ; Roberts, Mark L. ; Lardie Gaylord, Mary C.
    We present a low-cost, high-throughput method for converting many types of organic samples into graphite. The method combines sample combustion and graphitization in a single process. Using a modified sealed graphitization method, samples are placed in a Pyrex tube containing zinc, titanium hydride and iron catalyst. The tube is evacuated, flamed sealed, and placed in a muffle furnace for 7 hours. Graphite forms on the iron and is then analyzed for 14C content using either of NOSAMS’s two AMS systems. This method has been shown to work on a variety of organic samples including pure compounds, wood, peat, collagen and humics. This simplified procedure could be especially useful in reconnaissance studies in which it is desired to rapidly measure a large number of samples (untreated or pretreated), at low-cost with analytical precision and accuracy approaching that of traditional hydrogen reduction methods.
  • Article
    Erroneously old radiocarbon ages from terrestrial pollen concentrates in Yellowstone Lake, Wyoming, USA
    (Cambridge University Press, 2020-12-03) Schiller, Christopher M. ; Whitlock, Cathy ; Elder, Kathryn L. ; Iverson, Nels A. ; Abbott, Mark B.
    Accelerator mass spectrometry (AMS) dating of pollen concentrates is often used in lake sediment records where large, terrestrial plant remains are unavailable. Ages produced from chemically concentrated pollen as well as manually picked Pinaceae grains in Yellowstone Lake (Wyoming) sediments were consistently 1700–4300 cal years older than ages established by terrestrial plant remains, tephrochronology, and the age of the sediment-water interface. Previous studies have successfully utilized the same laboratory space and methods, suggesting the source of old-carbon contamination is specific to these samples. Manually picking pollen grains precludes admixture of non-pollen materials. Furthermore, no clear source of old pollen grains occurs on the deglaciated landscape, making reworking of old pollen grains unlikely. High volumes of CO2 are degassed in the Yellowstone Caldera, potentially introducing old carbon to pollen. While uptake of old CO2 through photosynthesis is minor (F14C approximately 0.99), old-carbon contamination may still take place in the water column or in surficial lake sediments. It remains unclear, however, what mechanism allows for the erroneous ages of highly refractory pollen grains while terrestrial plant remains were unaffected. In the absence of a satisfactory explanation for erroneously old radiocarbon ages from pollen concentrates, we propose steps for further study.
  • Article
    Radiocarbon in dissolved organic carbon by UV oxidation: an update of procedures and blank characterization at NOSAMS
    (Cambridge University Press, 2022-02-11) Xu, Li ; Roberts, Mark L. ; Elder, Kathryn L. ; Hansman, Roberta L. ; Gagnon, Alan R. ; Kurz, Mark D.
    This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 ± 0.6 μg C, with Fm of 0.42 ± 0.10 and δ13C of –28.43 ± 1.19‰. The throughput is improved from one sample per day to two samples per day.
  • Article
    Advances in Sample Preparation at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS): Investigation of Carbonate Secondary Standards
    ( 2017) Cruz, Anne J. ; Childress, Laurel B. ; Gagnon, Alan R. ; McNichol, Ann P. ; Burton, Joshua R. ; Elder, Kathryn L. ; Lardie Gaylord, Mary C. ; Gospodinova, Kalina D. ; Hlavenka, Joshua ; Kurz, Mark D. ; Longworth, Brett E. ; Roberts, Mark L. ; Trowbridge, Nan Y. ; Walther, Tess ; Xu, Li
    The development of robust sample preparation techniques for ocean science research has been a hallmark of NOSAMS since its inception. Improvements to our standard methods include reducing the minimum size of the samples we can analyze, building modular graphite reactors of different sizes that we can swap in and out depending on our sample stream, and modifying our carbonate acidification methods to improve handling of the smaller samples we now receive. A relatively new instrument, the Ramped PyrOx, which allows the separation of organic matter into thermal fractions, has attracted much interest as a research and development tool. We will also discuss our progress on incorporating a Picarro isotope analyzer into our sample preparation options.
  • Article
    The passage of the bomb radiocarbon pulse into the Pacific Ocean
    (Dept. of Geosciences, University of Arizona, 2010-08) Jenkins, William J. ; Elder, Kathryn L. ; McNichol, Ann P. ; von Reden, Karl F.
    We report and compare radiocarbon observations made on 2 meridional oceanographic sections along 150°W in the South Pacific in 1991 and 2005. The distributions reflect the progressive penetration of nuclear weapons-produced 14C into the oceanic thermocline. The changes over the 14 yr between occupations are demonstrably large relative to any possible drift in our analytical standardization. The computed difference field based on the gridded data in the upper 1600 m of the section exhibits a significant decrease over time (approaching 40 to 50‰ in Δ14C) in the upper 200–300 m, consistent with the decadal post-bomb decline in atmospheric 14C levels. A strong positive anomaly (increase with time), centered on the low salinity core of the Antarctic Intermediate Water (AAIW), approaches 50–60‰ in Δ14C, a clear signature of the downstream evolution of the 14C transient in this water mass. We use this observation to estimate the transit time of AAIW from its “source region” in the southeast South Pacific and to compute the effective reservoir age of this water mass. The 2 sections show small but significant changes in the abyssal 14C distributions. Between 1991 and 2005, Δ14C has increased by 9‰ below 2000 m north of 55°S. This change is accompanied overall by a modest increase in salinity and dissolved oxygen, as well as a slight decrease in dissolved silica. Such changes are indicative of greater ventilation. Calculation of “phosphate star” also indicates that this may be due to a shift from the Southern Ocean toward North Atlantic Deep Water as the ventilation source of the abyssal South Pacific.
  • Preprint
    Comparative AMS radiocarbon dating of pretreated versus non-pretreated tropical wood samples
    ( 2009-10) Patrut, Adrian ; von Reden, Karl F. ; Lowy, Daniel A. ; Mayne, Diana H. ; Elder, Kathryn L. ; Roberts, Mark L. ; McNichol, Ann P.
    Several wood samples collected from Dorslandboom, a large African baobab (Adansonia digitata L.) from Namibia, were investigated by AMS radiocarbon dating subsequent to pretreatment and, alternatively, without pretreatment. The comparative statistical evaluation of results showed that there were no significant differences between fraction modern values and radiocarbon dates of the samples analyzed after pretreatment and without pretreatment, respectively. The radiocarbon date of the oldest sample was 993 ± 20 BP. Dating results also revealed that Dorslandboom is a multi-generation tree, with several stems showing different ages.
  • Article
    A high-performance 14C accelerator mass spectrometry system
    (Dept. of Geosciences, University of Arizona, 2010-08) Roberts, Mark L. ; Burton, Joshua R. ; Elder, Kathryn L. ; Longworth, Brett E. ; McIntyre, Cameron P. ; von Reden, Karl F. ; Han, Baoxi ; Rosenheim, Brad E. ; Jenkins, William J. ; Galutschek, Ernst ; McNichol, Ann P.
    A new and unique radiocarbon accelerator mass spectrometry (AMS) facility has been constructed at the Woods Hole Oceanographic Institution. The defining characteristic of the new system is its large-gap optical elements that provide a larger-than-standard beam acceptance. Such a system is ideally suited for high-throughput, high-precision measurements of 14C. Details and performance of the new system are presented.
  • Article
    C-14 Blank Corrections for 25-100 mu G samples at the National Ocean Sciences AMS Laboratory
    (Cambridge University Press, 2019-07-22) Roberts, Mark L. ; Elder, Kathryn L. ; Jenkins, William J. ; Gagnon, Alan R. ; Xu, Li ; Hlavenka, Joshua ; Longworth, Brett E.
    Replicate radiocarbon (14C) measurements of organic and inorganic control samples, with known Fraction Modern values in the range Fm = 0–1.5 and mass range 6 μg–2 mg carbon, are used to determine both the mass and radiocarbon content of the blank carbon introduced during sample processing and measurement in our laboratory. These data are used to model, separately for organic and inorganic samples, the blank contribution and subsequently “blank correct” measured unknowns in the mass range 25–100 μg. Data, formulas, and an assessment of the precision and accuracy of the blank correction are presented.