• Improved AMS 14C Dating of Shell Carbonates Using High-Precision X-Ray Diffraction and a Novel Density Separation Protocol (CarDS)

      Douka, K.; Hedges, R. E. M.; Higham, T. F. G. (Department of Geosciences, The University of Arizona, 2010-01-01)
      One critical variable in the successful application of radiocarbon dating is the effective removal of carbonaceous contaminants. In the case of marine carbonates, contamination appears usually in the form of secondary low-magnesium calcite, the stable polymorph of calcium carbonate and byproduct of the post-mortem recrystallization or replacement of the autochthonous phase, originally in the form of high-magnesium calcite or aragonite. Depending on the nature of the depositional environment, the secondary phase may be contemporary in age with the original shell carbonate and may have even been derived from it by dissolution-recrystallization processes, or can be an exogenous contaminant of younger or older age. The limited ability of current pretreatment protocols to detect and remove the secondary mineralogical phases prior to dating carbonates has been one of the reasons marine shell and coral 14C determinations are often difficult to validate in terms of their reliability. We have developed a new pretreatment protocol designed to achieve greater reliability and accuracy in the dating of this material. The method entails 2 steps. The first one involves the improved detection and quantification of secondary calcite in aragonite using X-ray diffraction, at a precision of ~0.1% and ~0.8%, respectively. Next, where this is required, a novel density separation step using non-toxic heavy liquids (CarDS) is applied to the diagenetic sample. This enables the clear separation of calcite and aragonite, with only the latter kept for dating. We have applied the new steps, screening and separation, on standard and archaeological examples and our initial results suggest that it is successful and reproducible. In this paper, we describe the method and initial results.
    • Improved Application of Bomb Carbon in Teeth for Forensic Investigation

      Wang, N.; Shen, C. D.; Ding, P.; Yi, W. X.; Sun, W. D.; Liu, K. X.; Ding, X. F.; Fu, D. P.; Yuan, J.; Yang, X. Y.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      While radiocarbon is widely applied in dating ancient samples, recent studies reveal that 14C concentrations in modern samples can also yield precise ages due to the atmospheric testing of thermonuclear devices between 1950 and 1963. 14C concentrations in both enamel and organic matter of 13 teeth from 2 areas in China were examined to evaluate and improve this method of forensic investigation. Choosing enamel near the cervix of the tooth can reduce the error caused by the difference between the sample formation time and whole enamel formation time because tooth enamel formations take a long time to complete. A proper regional data set will be helpful to get an accurate result when calculating the age of the sample (T1) by the CALIBomb program. By subtracting the enamel formation time (t), the birth date of an individual (T2) can be confirmed by enamel F14C from 2 teeth formed at different ages. Calculated enamel formation dates by 14C concentration are basically consistent with corresponding actual values, with a mean error of 1.9 yr for all results and 0.2 yr for the samples formed after AD 1960. This method is more effective for dating samples completed after AD 1960. We also found that 14C concentrations in organic matter of tooth roots are much lower than atmospheric concentrations in root formation years, suggesting that the organic material keeps turning over even after tooth formation is complete. This might be a potential tool for identification of death age to extract a proper component for 14C dating. We also observed that delta-13C values between hydroxyapatite and organic matter indicate that isotopic fractionation during the biomineralization is 8-9‰ more positive in mineral fractions than in organic matter.
    • Investigating a Dated Piece of the Shroud of Turin

      Freer-Waters, Rachel A.; Jull, A. J. Timothy (Department of Geosciences, The University of Arizona, 2010-01-01)
      We present a photomicrographic investigation of a sample of the Shroud of Turin, split from one used in the radiocarbon dating study of 1988 at Arizona. In contrast to other reports on less-documented material, we find no evidence to contradict the idea that the sample studied was taken from the main part of the shroud, as reported by Damon et al. (1989). We also find no evidence for either coatings or dyes, and only minor contaminants.
    • Is More Precise Dating of Paleoindian Expansion Feasible?

      Fiedel, S. J.; Kuzmin, Y. V. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Recent efforts to precisely date the florescence of the Clovis culture in North America have been hampered by both practical and theoretical problems: 1) The era of Clovis expansion (about 11,200-10,700 BP or 13,200-12,700 cal BP) coincides with the gap between the anchored central European tree-ring sequence (back to 12,400 cal BP) and the floating Bolling-Allerod sequence; 2) Clovis seems to immediately precede the onset of the Younger Dryas (YD) stadial. The "black mats" of the US Southwest appear to mark the regional occurrence of this climatic downturn. However, the timing and means of long-distance propagation of this climatic event are not yet well understood. Greenland ice cores (GISP2, GRIP, and NGRIP) remain poorly synchronized, with a discrepancy of 100 to 250 yr for the date of onset (as late as 12,700 cal BP, or as early as 12,950 cal BP); 3) The YD onset was accompanied by a rapid drop of radiocarbon ages from 11,000 to 10,600 BP in less than a century. The mechanism causing this was probably a change in overturning circulation in the North Atlantic. Do variable Clovis ages, often from what appear to be single-occupation contexts, reflect this "cliff" effect, slightly earlier minor reversals during the late Allerd, or simply the practical limitations of precision of the 14C method? 4) Dates for Fishtail or Fell I sites (with fluted, stemmed points) in southern South America are statistically indistinguishable from Clovis dates in North America. Does this imply very rapid population expansion, diffusion of tool-making techniques through long-established local populations (as argued by Waters and Stafford 2007), or abnormally large interhemispheric 14C offsets? 5) Are recent ostensibly high-precision collagen-derived dates for Paleoindian-associated fauna (e.g. horse and mammoth) reliable? Are interlaboratory blind tests of the new filtration processes necessary?
    • Is the Consensus Value of ANU Sucrose (IAEA C-6) Too High?

      Xu, Xiaomei; Khosh, Matthew S.; Druffel-Rodriguez, Kevin C.; Trumbore, Susan E.; Southon, John R. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Primary and secondary standards are essential in radiocarbon analyses for the purpose of reporting and comparing data among laboratories, as well as for internal laboratory data quality control. ANU sucrose is one of the IAEA-certified 14C standards (C-6) with a consensus value of 1.5061 +/- 0.0011 fraction modern (Fm). All of our measurements of ANU sucrose (n = 351) as a secondary standard over the last 7 yr result in an average value of 1.5016 +/- 0.0005 Fm (2- standard error). After applying the same outlier tests used for IAEA reference standards, a weighted average value of 1.5016 +/- 0.0002 Fm (n = 294) was calculated. This value is significantly lower than the IAEA C-6 consensus value (t test with unequal variance; p = 0.023). In contrast, our measurements of other secondary standards over the same time period are in excellent agreement with their respective consensus values. Since ANU is the only secondary standard measured in our lab that does not agree with the consensus values, and we have measured a larger number analyses compared to what went into the definition of the consensus value, we suggest that the consensus value of ANU sucrose might be too high by ~0.0045 +/- 0.0011 Fm. Given that some labs routinely use ANU sucrose as a primary standard, our results suggest that revisiting the consensus value of ANU sucrose may be necessary.
    • 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.