• Laser-Heated Microfurnace: Gas Analysis and Graphite Morphology

      Smith, A. M.; Yang, B.; Hua, Q.; Mann, M. (Department of Geosciences, The University of Arizona, 2010-01-01)
      We describe progress in developing a novel miniaturized laser-heated 'microfurnace' aimed at preparing ultra-small (~5 g) graphite samples from CO2 (Smith et al. 2006, 2007, 2010). Recent effort has focused on automation of the process using a LabVIEW interface, which has permitted feedback control of the catalyst temperature as the reaction proceeds and the logging of reaction parameters. We trialed a number of different pure iron catalysts as well as Fe2O3 (which is reduced in situ to iron) and discuss the reaction rates. We studied the graphite morphology by scanning electron microscopy (SEM) and found there is a marked difference in graphite morphology with catalyst type. We assessed how each catalyst performs in the cesium sputter ion source of the ANTARES Accelerator Mass Spectrometry (AMS) facility. We utilized a quadrupole mass spectrometer to study the gas composition during the reaction, in order to better understand the underlying chemical reactions for such small samples and to better estimate the overall efficiency of the process. Results show that all CO2 is converted to CO by reduction on the iron catalyst within a few minutes of applying laser power. The reaction pressure stabilizes after 40 min; however, some CO is not converted to graphite. The cold trap temperature of -80 C is effective at trapping H2O, so there is little CH4 production.
    • Letter from the Editor

      Jull, A. J. T. (Department of Geosciences, The University of Arizona, 2010-01-01)
    • Measuring Submicron-Size Fractionated Particulate Matter on Aluminum Impactor Disks

      Buchholz, B. A.; Zermeño, P.; Wang, H-M.; Young, T. M.; Guilderson, T. P. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Submicron-sized airborne particulate matter (PM) is not collected well on regular quartz or glass fiber filter papers. We used a micro-orifice uniform deposit impactor (MOUDI) to fractionate PM into 6 size fractions and deposit it on specially designed high-purity thin aluminum disks. The MOUDI separated PM into fractions 56-100, 100-180, 180-320, 320-560, 560-1000, and 1000-1800 nm. Since the MOUDI has a low flow rate (30 L/min), it takes several days to collect sufficient carbon on 47-mm foil disks. The small carbon mass (20-200 g C) and large aluminum substrate (~25 mg Al) present several challenges to production of graphite targets for accelerator mass spectrometry (AMS) analysis. The Al foil consumes large amounts of oxygen as it is heated and tends to melt into quartz combustion tubes, causing gas leaks. We describe sample processing techniques to reliably produce graphitic targets for 14C AMS analysis of PM deposited on Al impact foils.
    • MICADAS: Routine and High-Precision Radiocarbon Dating

      Wacker, L.; Bonani, G.; Friedrich, M.; Hajdas, I.; Kromer, B.; Němec, N.; Ruff, M.; Suter, M.; Synal, H.-A.; Vockenhuber, C. (Department of Geosciences, The University of Arizona, 2010-01-01)
      The prototype mini carbon dating system (MICADAS) at ETH Zurich has been in routine operation for almost 2 yr. Because of its simple and compact layout, setting up a radiocarbon measurement is fast and the system runs very reliably over days or even weeks without retuning. The stability of the instrument is responsible for the good performance in highest-precision measurements where results of single samples can be reproduced within less than 2. The measurements are described and the performance of MICADAS is demonstrated on measured data.
    • Modern Radiocarbon Levels for Northwestern Mexico Derived from Tree Rings: A Comparison with Northern Hemisphere Zones 2 and 3 Curves

      Beramendi-Orosco, Laura E.; Gonzalez-Hernandez, Galia; Villanueva-Diaz, Jose; Santos-Arevalo, Francisco J.; Gómez-Martinez, Isabel; Cienfuegos-Alvarado, Edith; Morales-Puente, Pedro; Urrutia-Fucugauchi, Jamie (Department of Geosciences, The University of Arizona, 2010-01-01)
      The radiocarbon variation for northwestern Mexico during the period 1950-2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18 degrees N, 106.3 degrees W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a ∆14C value of 713.15 +/- 9.3‰. The values obtained for the period 1958-1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975-2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2.
    • NERC Radiocarbon Age Measurements Determined by Radiometric Counting 1996–2005

      Garnett, M. H.; Harkness, D. D.; Miller, B. F.; Fallick, A. E.; Bryant, C. L. (Department of Geosciences, The University of Arizona, 2010-01-01)
      We describe a new compilation of radiocarbon age measurements performed by the NERC Radiocarbon Laboratory that is freely available to access over the World Wide Web. The database contains 1000 14C measurements performed using the liquid scintillation counting method between 1996 and 2005, and further results will be added as the information is compiled. Contextual information including sampling location and the nature of sample material is provided, alongside 14C age results and publications codes. Hypertext links provide access to the original 14C age report associated with the samples, providing additional details. The 14C measurements were originally performed for earth and environmental science NERC projects and are therefore likely to be most relevant to the Quaternary research community.
    • New Dating Evidence for North Sea Trade between England, Scotland, and Norway in the 11th Century AD

      Hall, D. W.; Cook, G. T.; Hamilton, W. D. (Department of Geosciences, The University of Arizona, 2010-01-01)
      This study follows on from previous research at Perth, Scotland, in which we dated carbonized food residues removed from the external surface of rim sherds of cooking pots of London Sandy Shellyware pottery (Museum of London Pottery Fabric Code SSW). The 15 residues that were dated produced 14C ages between 910 +/- 35 and 1085 +/- 40 BP. We have now carried out radiocarbon measurements on similar residues from the same fabric obtained from the Billingsgate excavations in London and the Bryggen excavations in Bergen, Norway. The London and Bergen measurements gave age ranges of 905 +/- 35 to 1115 +/- 35 BP and 920 +/- 35 to 1055 +/- 35 BP, respectively, both very similar to the Perth age range. The measurements at each site are in agreement with our Bayesian model assumption that they belong to a single phase of activity. The model estimates the introduction of London Sandy Shellyware in London to cal AD 820-1020, in Perth to cal AD 930-1020, and in Bergen to cal AD 980-1030 (95% probability). Further modeling predicts that it fell out of use in the reverse order.
    • New Radiocarbon Dates from the Late Neolithic Tell Settlement of Hódmezővásárhely-Gorzsa, SE Hungary

      Gulyás, Sandor; Sümegi, Pál; Molnár, Mihály (Department of Geosciences, The University of Arizona, 2010-01-01)
      Understanding the internal chronology of the Late Neolithic Tisza culture and the Neolithic of the Tisza region is the subject of debate in both Hungarian and international prehistoric research. The layer sequence of the Late Neolithic Gorzsa tell from SE Hungary offers ideal match points for determining the successive phases of the Tisza culture. According to the results published so far, in the Gorzsa sequence the Tisza culture was divided into 4 main phases with a fifth phase representing the transitional period to the Early Copper Age. Excavations were carried out in 33 profiles covering about 2% of the original area of the entire settlement. The archaeostratigraphy established was based on the identification of microhorizons corresponding to settlement levels. Radiocarbon dates published thus far were created using a pool of various objects of differing microhorizons deriving from different profiles. However, as archaeological results revealed, the settlement was characterized by frequent, minor spatial shifts during its evolution into a tell complex. Here, we present a succession of 7 14C dates deriving from a single profile located at the northeastern flank of the excavation area. The 7 dates span the entire profile from the uppermost microhorizons down to the lowermost ones. The new dates were compared with the existing relative chronology mentioned above. According to our findings, material was deposited in this part of the site mainly during the first 2 phases of evolution of the tell complex. The later phases are either less developed or missing due to possibly a spatial shift of the center of the tell complex resulting first in a deceleration and finally a complete cessation of artifact accumulation to the northwest flanks of the former natural levee. Thus, the previous hypothesis of spatial shifts based on relative chronologies within the site has been corroborated. Furthermore, the congruence between our new dates corrected for any reservoir effect and the previous dates of Hertelendi (1998) may refer to a correct determination of freshwater shell carbonate reservoir effect in the fluvial system of the Tisza River, which may be used in further studies in the area.
    • Obituary: Austin Long

      Eastoe, C.; Leavitt, S.; Tanner Elliott, K.; Sewell, D. (Department of Geosciences, The University of Arizona, 2010-01-01)
    • On-Line Radiocarbon Measurements of Small Samples Using Elemental Analyzer and MICADAS Gas Ion Source

      Ruff, M.; Fahrni, S.; Gaggeler, H. W.; Hajdas, I.; Suter, M.; Synal, H-A; Szidat, S.; Wacker, L. (Department of Geosciences, The University of Arizona, 2010-01-01)
      An on-line measurement system was installed at the MICADAS in Zurich, using an elemental analyzer (EA) as a combustion unit to enable direct radiocarbon measurement of samples containing carbon in the range of 5-100 g possible with minimum effort. The samples are combusted in small capsules and the gaseous combustion products are separated by the EA. The carbon dioxide leaving the EA in a high helium flow is concentrated on a small external trap containing X13 zeolite adsorber material. This new concept, avoiding a cryogenic trapping for the enrichment step, allows the construction of a very compact system able to work even with the smallest samples. Concentrated on the external trap, the carbon dioxide is flushed into the gas-tight syringe of our gas inlet system using a low helium stream. The gas mixture is measured with the MICADAS gas ion source. Several different sample capsules were analyzed to minimize the major blank contribution coming from the sample vessel. The best results were achieved with 25-L tin capsules, which contained only 0.34 0.13 g carbon at 65 pMC. This work describes the development of the on-line system and the protocol for measurement runs. Results are presented for on-line measurements of reference materials and a comparison is performed with typical dating samples measured previously as graphite targets. Finally, relevance and limitations of on-line measurements are discussed.
    • Optimization of 236U AMS at CIRCE

      De Cesare, Y.; Quinto, F.; Sabbarese, C.; D, N.; D'Onofrio, A.; Alanella, L.; Petraglia, A.; Roca, V.; Terrasi, F. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Actinide isotopes are present in environmental samples at ultra-trace levels (236U concentration is quoted to be on the order of pg/kg or fg/kg). Their detection requires the resolution of mass spectrometry (MS) techniques, but only accelerator mass spectrometry (AMS) has the sensitivity required. In order to perform the isotopic ratio measurements of actinides, such as 236U/238U, an upgrade of the Center for Isotopic Research on Cultural and Environmental Heritage accelerator (CIRCE) in Caserta, Italy, has been performed. The system was originally equipped for radiocarbon AMS measurements. The main difficulty of AMS measurement of 236U is the intense neighboring beam of 238U. Although most of the 238U ions are suppressed by means of magnetic and electrostatic elements, a small fraction of this intense beam can interfere with the rare isotopes. This paper reports the preliminary results of the 236U/238U isotopic ratio measurement limit 5.6 x 10^(-11)), aimed also to better understand the origin of background ions. For this purpose, a large 16-strip silicon detector providing spatial resolution has been used. In addition, calculations to assess the performance of the system obtained by adding a high-resolution time of flight-energy (TOF-E) detector are discussed.
    • Optimization of the Graphitization Process at AGE-1

      Němec, Mojmir; Wacker, Lukas; Gäggeler, Heinz (Department of Geosciences, The University of Arizona, 2010-01-01)
      The reaction conditions for the graphitization of CO2 with hydrogen were optimized for a fast production of high-quality carbon samples for accelerator mass spectrometry (AMS) measurement. The iron catalyst in use is first oxidized by heating with air to remove possible carbon and other impurities and then after evacuation reduced back to iron with hydrogen in several flushing steps to remove any iron oxide. The optimum conditions for a fast graphitization reaction were experimentally determined by changing the reaction temperatures and the H2/CO2 ratio. The resulting graphite samples were measured by AMS to find the smallest isotopic changes (13C) at a minimum of molecular fragment formation (13CH current). The improvements are based on thermodynamic data and are explained with Baur-Glaessner diagrams.
    • Paleodiet Reconstruction of Human Remains from the Archaeological Site of Natfieh, Northern Jordan

      Al-Bashaireh, K.; Al-Shorman, A.; Rose, J.; Jull, A. J. T.; Hodgins, G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      This investigation concerns human teeth and bones from the site of Natfieh, north Jordan. Nitrogen and carbon isotope analyses were used to model the paleo-economy by reconstructing Natfieh's paleodiet during a specific time period. 14C dating of human teeth and bones from the site of Natfieh, north Jordan, demonstrate that they belong to the Early Roman period and match the archaeological date from the tomb and grave goods typology. Stable isotope analyses of these humans have provided new information about the subsistence and society of individuals buried at Natfieh. Natfieh is today agriculturally productive and must have been so in antiquity with most of the foodstuffs having been produced locally. The long distance between Natfieh and the closest aquatic food source (Mediterranean Sea and Lake Tiberias) and the high cost of land transportation might be the reason for the low consumption of marine protein. The results agree with past research on the Roman diet showing that plants were the common source of food for the Romans and fish may have been restricted to elite members of the society.
    • Paleoearthquakes as Anchor Points in Bayesian Radiocarbon Deposition Models: A Case Study from the Dead Sea

      Kagan, Elisa J.; Stein, Mordechai; Agnon, Amotz; Ramsey, Christopher Bronk (Department of Geosciences, The University of Arizona, 2010-01-01)
      The Bayesian statistical method of the OxCal v 4.1 program is used to construct an age-depth model for a set of accelerator mass spectrometry (AMS) radiocarbon ages of organic debris collected from a late Holocene Dead Sea stratigraphic section (the Ein Feshkha Nature Reserve). The model is tested for a case where no prior earthquake information is applied and for a case where there is incorporation of known ages of 4 prominent historical earthquakes as chronological anchor points along the section. While the anchor-based model provided a tightly constrained age-depth regression, the "non-anchored" model still produces a correlation where most of the 68% or 95% age ranges of the 52 seismites can be correlated to historical earthquakes. This presents us with the opportunity for high-resolution paleoseismic analysis and comparison between various sites.
    • Paleoenvironment of Medieval Archaeological Sites in Central Japan: Assemblage Analysis and 14C Dating of Insect Fossils

      Okuno, E.; Mori, Y.; Nakamura, T. (Department of Geosciences, The University of Arizona, 2010-01-01)
      This study aimed to investigate the paleoenvironment of 2 Medieval archaeological sites, Onigashioya and Ooke, in central Japan, by assemblage analyses of insect fossils preserved in sediments at the sites. In the Onigashioya site located in Mie Prefecture, the sclerites of insect fossils classified as the "village" type were detected, which indicates that human activities, and in particular farming, were taking place there. Rice paddies and fields existed near the site, which explains why many insects harmful to rice plants and crops were detected in the area. The radiocarbon date for sclerite remains of Hydrophilus acuminatus, an aquatic beetle that live in rice paddy fields, was calibrated to be cal AD 1010-1155. Analysis of sclerite remains of Craspedonotus tibialis, a ground beetle that typically inhabits seashore environments, resulted in a date of cal AD 1020-1155. This finding suggests that human settlements existed in the seaside areas of the Onigashioya site in the 11th century AD. In the Ooke site located in Aichi Prefecture, "insect pits" were found, which are structural remains containing a large number of Anomala rufocuprea, an insect that preys on field crops. Farmers would have gathered the insects from the fields and buried the dead remains in the pits. Accelerator mass spectrometry (AMS) 14C dates on sclerite remains of A. rufocuprea ranged from cal AD 1264 to 1385. It should be noted that fruit trees and vegetable crops were planted widely around the site in the 13th century AD. As the result, A. rufocuprea propagated greatly around the site in that period. It is probable that many insects harmful to field crops multiplied largely in this region due to the development of local woods and plains into farming fields. This type of development occurred throughout Japan during the Medieval period.
    • Personal Recollections of a Good Experiment

      Nelson, E. (Department of Geosciences, The University of Arizona, 2010-01-01)
    • Pre-Bomb Marine Reservoir Ages in the Western Pacific

      Yoshida, Kunio; Hara, Tatsuaki; Kunikita, Dai; Miyazaki, Yumiko; Sasaki, Takenori; Yoneda, Minoru; Matsuzaki, Hiroyuki (Department of Geosciences, The University of Arizona, 2010-01-01)
      In this study, molluscan shells housed at the University Museum, the University of Tokyo, provided a new set of region-specific correction values (R) for the western Pacific, in particular for the central part of the main islands in the Japanese Archipelago and the southwest islands of Japan. The values of 40 total samples were calculated from 11 regions. North of the main islands and in the Ryukyu Islands, the mean R values showed comparatively small values, 5-40 14C yr; in the central part of the main islands, these values were 60-90 14C yr.
    • Pre-Bomb Marine Reservoir Variability in the Kimberley Region, Western Australia

      O'Connor, Sue; Ulm, Sean; Fallon, Stewart J.; Barham, Anthony; Loch, Ian (Department of Geosciences, The University of Arizona, 2010-01-01)
      New Delta-R values are presented for 10 known-age shells from the Kimberley region of northwest Australia. Previous estimates of Delta-R for the Kimberley region are based on only 6 individual shell specimens with dates of live collection known only to within 50 yr (Bowman 1985a). Here, we describe the results of our recent attempts to constrain Delta-R variability for this region by dating a suite of known-age pre-AD 1950 shell samples from the Australian Museum and Museum Victoria. A regional Delta-R of 58 +/- 17 14C yr for open waters between Broome and Cape Leveque is recommended based on 7 of these specimens. The criteria used to select shells for dating and inclusion in the regional mean are discussed.
    • Precise Comparison of 14C Ages from Choukai Jindai Cedar with IntCal04 Raw Data

      Suzuki, Kayo; Sakurai, Hirohisa; Takahashi, Yui; Sato, Taiichi; Gunji, Shuichi; Tokanai, Fuyuki; Matsuzaki, Hiroyuki; Tsuchiya, Yoko (Department of Geosciences, The University of Arizona, 2010-01-01)
      We measured the radiocarbon ages of 165 single-year tree rings from a Japanese Choukai Jindai cedar using accelerator mass spectrometry (AMS). By wiggle-matching the Choukai_AMS data set to the IntCal04 calibration data using OxCal v 3.10 and using the variation of the correlation coefficients between the Choukai_AMS and IntCal04 data sets, we precisely re-estimated that the 321 Choukai Jindai cedar tree rings range from 780 to 460 cal BC with an accuracy of 8 yr. The Choukai_AMS data set is older than the 3 raw data sets of European tree rings that comprise IntCal04. The Belfast and Seattle data sets are younger by -21.3 +/- 5.5 and -22.7 +/- 5.6 14C yr, respectively. The Choukai Jindai cedar is ~22 14C yr older than the European tree rings, which is equivalent to an offset of -2.8‰ in 14C. In addition, the Choukai_AMS data set correlates well with the Belfast and Seattle data sets, with correlation coefficients of 0.89 and 0.68, respectively, between the temporal profiles. Hence, the temporal profile of the Choukai 14C ages shows a global variation.
    • Radiocarbon AMS Data Analysis: From Measured Isotopic Ratios to 14C Concentrations

      Zoppi, Ugo (Department of Geosciences, The University of Arizona, 2010-01-01)
      Radiocarbon accelerator mass spectrometry (AMS) measurements are always carried out relative to internationally accepted standards with known 14C activities. The determination of accurate 14C concentrations relies on the fact that standards and unknown samples must be measured under the same conditions. When this is not the case, data reduction is either performed by splitting the collected data set into subsets with consistent measurement conditions or by applying correction factors. This paper introduces a mathematical framework that exploits the intrinsic variability of an AMS system by combining arbitrary measurement parameters into a normalization function. This novel approach allows the en-masse reduction of large data sets by providing individual normalization factors for each data point. Both general features and practicalities necessary for its efficient application are discussed.