• 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.
    • 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
    • 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.
    • 14C Ages of 43 Consecutive Single-Year Tree Rings Between 2710 and 2655 cal BP Using Accelerator Mass Spectrometry

      Suzuki, Kayo; Sakurai, Hirohisa; Takahashi, Yui; Gunji, Shuichi; Tokanai, Fuyuki; Matsuzaki, Hiroyuki; Sunohara, Yoko (Department of Geosciences, The University of Arizona, 2007-01-01)
      We have measured the radiocarbon ages of 43 consecutive single-year tree rings using accelerator mass spectrometry (AMS) with a statistical accuracy of -2.3 AMS 14C ages of the 36 viable samples are between 2708 and 2666 cal BP, a period in which the 14C of the IntCal04 curve (Reimer et al. 2004) shows an enhancement. The 14C ages of the samples are scattered with a Gaussian distribution around the interpolated IntCal04 calibration curve. The time profile of the deviations of the 36 14C ages from the interpolated IntCal04 calibration curve indicates a linear trend and a characteristic variability rather than a random fluctuation around the curve. The trend indicates a higher gradient than that of the interpolated IntCal04 calibration curve. The profile implies a periodic variation of approximately 11 yr and an amplitude of roughly 18 14C yr.
    • 14C Ages of a Varved Last Glacial Maximum Section Off Pakistan

      von Rad, Ulrich; Sarnthein, Michael; Grootes, Pieter M.; Doose-Rolinski Heidi; Erbacher, Jochen (Department of Geosciences, The University of Arizona, 2003-01-01)
      In a core off Pakistan, we obtained 38 14C analyses by accelerator mass spectrometry (AMS) from a 4.4-m-thick, expanded, annually-laminated Last Glacial Maximum (LGM) section, bracketed by bioturbated intervals ascribed to the Heinrich-1 (H1) and Heinrich-2 (H2) equivalent events (52 14C analyses between 24-15 kyr BP). A floating varve age scale, anchored to the oxygen isotope record of the layer-counted GISP2 ice core at the H2/LGM boundary, results in an annually dated record for the LGM from 23,450-17,900 cal BP. The floating varve scale of the LGM provides us with a tentative calibration of local marine AMS 14C age dates to calendar years.
    • 14C Ages of Bone Fractions from Armenian Prehistoric Sites

      Cherkinsky, A.; Chataigner, C. (Department of Geosciences, The University of Arizona, 2010-01-01)
      Prehistoric cultures in Armenia are still poorly known; thus, accelerator mass spectrometry (AMS) radiocarbon dates are invaluable in constructing an accurate chronology. Bone samples have been collected from sites representing the Middle Paleolithic, Chalcolithic, and Early Bronze periods. Most of the bone samples are poorly preserved. We describe the separation technique for the extraction of both the bioapatite and collagen fractions. In many cases where the bone had very low organic material content, the collagen fractions yielded a younger age, although the ages of bioapatite fractions were found to be in good agreement with associated archaeological artifacts. In cases where bone was well preserved, both fractions exhibited ages in good agreement with the artifacts. The accuracy of 14C dating of bone material always depends on its degree of preservation, and each case should be carefully evaluated to determine which fraction is less contaminated in order to accurately date a burial event.
    • 14C Ages of Tephra Layers from the Holocene Deposits of Kunashir Island (Russian Far East)

      Razjigaeva, N. G.; Grebennikova, T. A.; Ganzey, L. A.; Bazarova, V. B.; Mokhova, L. M.; Korotky, A. M.; Sulerzhitsky, L. D. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Holocene deposits from the central and southern regions of the Kunashir Island contain tephra from 12 volcanic eruptions (Kn1-12). We studied radiocarbon data, mineralogical composition, and distribution of the tephra layers in different Holocene facies. The main sources of the Holocene tephra samples were the volcanoes of Hokkaido Island. The distribution of ash layers on Kunashir Island allows us to estimate their direction. Ash layers can be reliable markers for age determination of different coastal landforms on open oceanic shores. We propose here a tephrastratigraphical scheme for different Middle-Late Holocene facies.
    • 14C Ages of Terrestrial Macrofossils from Lago Grande di Monticchio (Italy)

      Hajdas, Irka; Bonani, Georges; Zolitschka, Bernd; Brauer, Achim; Negendank, Jörg W. (Department of Geosciences, The University of Arizona, 1998-01-01)
      Lago Grande di Monticchio (Italy) contains long sedimentary records of >75 ka (Zolitschka and Negendank 1996). In a joint European project (Creer and Thouveny 1996), vegetation history and climatic changes for this part of the Mediterranean have been reconstructed (Watts, Allen and Huntley 1996; Watts et al. 1996). In addition to the time scale based on annual laminations and sedimentation rate, tephra layers and pollen spectra, radiocarbon dating was applied for the last 40 ka. Previous studies have shown that the age of bulk sediment from Lago Grande di Monticchio, which is a maar lake at the flanks of Mt. Vulture, was influenced by "dead carbon" of volcanic origin dissolved in the lake water. Thus, 14C dating of the record is problematic and must be limited to dating macrofossils of terrestrial origin. From a set of sediment samples, macrofossils were selected and dated using accelerator mass spectrometry (AMS). A 14C time scale based on seven data points between 9000 and 24,000 BP is compared with other dating of the record based on varve counting and tephrochronology (Zolitschka 1996).
    • 14C AMS at SUERC: Improving QA Data with the 5MV Tandem and 250kV SSAMS

      Naysmith, P.; Cook, G. T.; Freeman, S. T.; Scott, E. M.; Anderson, R.; Xu, S.; Dunbar, E.; Muir, G. P.; Dougans, A.; Wilcken, K.; et al. (Department of Geosciences, The University of Arizona, 2010-01-01)
      In 2003, a National Electrostatics Corporation (NEC) 5MV tandem accelerator mass spectrometer was installed at SUERC, providing the radiocarbon laboratory with 14C measurements to 4-5 repeatability. In 2007, a 250kV single-stage accelerator mass spectrometer (SSAMS) was added to provide additional 14C capability and is now the preferred system for 14C analysis. Changes to the technology and to our operations are evident in our copious quality assurance data: typically, we now use the 134-position MC-SNICS source, which is filled to capacity. Measurement of standards shows that spectrometer running without the complication of on-line 13C evaluation is a good operational compromise. Currently, 3 14C/13C measurements are routinely achieved for samples up to nearly 3 half-lives old by consistent sample preparation and an automated data acquisition algorithm with sample random access for measurement repeats. Background and known-age standard data are presented for the period 2003-2008 for the 5MV system and 2007-2008 for the SSAMS, to demonstrate the improvements in data quality.
    • 14C AMS Dating of Icelandic Lake Sediments

      Sveinbjörnsdóttir, Árný E.; Heinemeier, Jann; Kristensen, Peter; Rud, Niels; Geirsdóttir, Áslaug; Harđardóttir, Jóhann (Department of Geosciences, The University of Arizona, 1998-01-01)
      We report an age-depth profile for the sediments of the Lake Hestvatn, southern Iceland, based on 14C analyses of the organic fraction of bulk sediment samples, molluscs and foraminifera. Our age-depth curve is supported by the occurrence of the well-dated Vedde ash in the lowermost part of the sediments. Comparison of foraminifera dates with the age of the Vedde ash indicates a reservoir age of ca. 400 yr. The results suggest that the sediments at Hestvatn accumulated in a marine environment until ca. 8700 BP and thereafter in freshwater. Owing to the lack of terrestrial macrofossils and the low concentration of molluscs and foraminifera, we were forced to attempt to date most of the core with the organic fraction of the bulk sediment samples. We found, however, that this fraction is not homogeneous in density or 14C age. We believe that during sample pretreatment we managed to isolate a light organic fraction, which closely represents the true age of the sediment, whereas the denser fraction yields ages that are too high. This age diversity may to some extent be explained by the large drainage area of the lake, from which plant remains of different ages may have been washed into the lake.
    • 14C AMS Dating the Transition from the Paleolithic to the Neolithic in South China

      Yuan, Sixun; Zhou, Guoxing; Guo, Zhiyu; Zhang, Zimo; Gao, Shijun; Li, Kun; Wang, Jiangjun; Liu, Kexing; Li, Bin; Lu, Xiangyang (Department of Geosciences, The University of Arizona, 1995-01-01)
      To study the transition from the Paleolithic to the Neolithic period and its duration, samples of charcoal, bone, flowstone and shells excavated from Bailiandong and Miaoyan caves, Guangxi Zhuang autonomous region, South China were dated using the Peking University AMS facility and liquid scintillation counter. The remains excavated from these sites show typical characteristics of the transition from the Paleolithic to the Neolithic. Radiocarbon dating results show a rapid transition from ca. 20 to 10 ka BP.