• Measurements of the Oxalic Acid II/Oxalic Acid I Ratio as a Quality Control Parameter at NOSAMS

      Schneider, R. J.; McNichoal, A. P.; Nadeau, M. J.; Vo, K. F. (Department of Geosciences, The University of Arizona, 1995-01-01)
      Precision of AMS single-target measurements is usually based on counting statistics and variance during the data acquisition cycle. Additional longer-term variability may be studied by looking at the variability of the standards from cycle to cycle.
    • Radiocarbon Age Assessment of a New, Near Background IAEA 14C Quality Assurance Material

      Hogg, A. G.; Higham, Thomas; Robertson, Steve; Beukens, Roelf; Kankainen, Tuovi; McCormac, F. G.; van der Plicht, Johannes; Stuiver, Minze (Department of Geosciences, The University of Arizona, 1995-01-01)
      The 14C Quality Assurance Programme coordinated by the IAEA (Rozanski  et al. 1992) prepared a set of five new intercomparison materials, including 40-50 ka old subfossil wood excavated from New Zealand peat bogs (IAEA C-4 standard). Statistical analysis of 79 14C measurements made on the wood indicated considerable variation in the results, with a marked skewness toward more modern values. The wide range of results and the possibility of inhomogeneity within the standard prompted the recovery and analysis of replacement material. The new subfossil wood sample is kauri (Agathis australis), at least 50 ka old, excavated from a swamp in Northland. It is in the form of a single plank, 6 m long, weighing 80 kg. It will be forwarded to the IAEA in Vienna for milling and distribution. Subsamples were obtained from both ends of the plank and analyzed by six laboratories. We present here the results of these analyses and compare them with the previous IAEA intercalibration results for the C-4 standard.
    • Radiocarbon and Thermoluminescence Studies of the Karst Pipe Systems in Southwest England and South Wales

      Pazdur, Mieczysław F.; Bluszcz, Andrzej; Pazdur, Anna; Morawiecka, Iwona (Department of Geosciences, The University of Arizona, 1995-01-01)
      Paleokarst forms in raised beach deposits of Southwest England and South Wales and generally known as "pipes" were dated by 14C and thermoluminescence (TL) methods. Current geological opinion is that these pipes are features that developed under the cover of periglacial-solifluctional deposits due to periglacial conditions prevalent in the Late Devensian. In the present study, TL was used to determine the age of quartz grains forming the raised beaches. 14C ages were obtained from carbonate cements within sandrock and on the pipe walls. TL ages measured for quartz grains separated from sandrock samples are older than 80 ka BP, whereas the corresponding TL dates obtained from the sandy material of pipe infills center around 40 ka BP. All carbonates yielded finite apparent 14C dates that range from ca. 45 ka BP to 27 ka BP for sandrock. The apparent 14C dates obtained on carbonate cements from the pipe walls fall into two groups, one ranging from 30 ka BP to 22 ka BP and the other from 15 ka BP to 7 ka BP. On the basis of geochemical considerations, we conclude that the sandrock cements formed between 35 and 25 ka BP and pipe walls cemented between 30 and 2 ka BP with a break during the climate deterioration caused by last ice sheet advance.
    • Problems in Dating Stone-Age Settlements on Sandy Soils: The Hof ten Damme Site Near Melsele, Belgium

      Van Strydonck, Mark J. Y.; van Roeyen, Jean-Pierre; Minnaert, Guido; Verbruggen, Cyriel (Department of Geosciences, The University of Arizona, 1995-01-01)
      Archaeological sites on sandy soils often suffer from dislocation of artifacts and datable materials. Because stratigraphy and context lose their meaning in such cases, all 14C dates in this study were put in a dispersion diagram regardless of the sample origin. We drew conclusions about the chronology of the site by comparing this diagram with archaeological analysis of the artifacts and the evolution of the landscape. The dating series, as well as the archaeological analysis, suggest several occupation phases. In general, the archaeological chronology agrees with the 14C dates, although the two can be equated only with caution.
    • Radiocarbon Age Offsets in Different-Sized Carbonate Components of Deep-Sea Sediments

      Thomson, John; Cook, G. T.; Anderson, Robert; MacKenzie, A. B.; Harkness, D. D.; McCave, I. N. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We compared accelerator mass spectrometry (AMS) 14C ages of large (>150 micrometers) pelagic foraminifera with radiometric bulk carbonate 14C ages in two northeastern Atlantic cores. The foraminiferal ages are consistently older than those of the bulk sediment (by + 0.76 ka in Core 11881 and by + 1.1 ka in Core 11886), whereas corresponding fine (<5 micrometers) fraction ages are similar to those of the bulk sediment carbonate. We calculated near-identical sediment accumulation rates from both the foraminiferal and bulk sediment age/depth relations (3.0 cm ka-1 in Core 11881 and 5.9 cm ka-1 in Core 11886). Consideration of various factors that might produce such offsets leads us to believe that they are not artifacts, but were most probably caused by differential bioturbation of the different size-fractions in the sediment surface mixed layer. The importance of this finding is that many paleoceanographic records, such as the oxygen isotope record, also derive from analyses of large foraminifera, so that these records must be offset in time from the bulk of the sediments that they characterize.
    • Radiocarbon Age of the Laacher See Tephra: 11,230 +/- 40 BP

      Hajdas, Irena; Ivy-Ochs, S. D.; Bonani, Georges; Lotter, André F.; Zolitschka, Bernd; Schlüchter, Christian (Department of Geosciences, The University of Arizona, 1995-01-01)
      The Laacher See Tephra (LST) layer provides a unique and invaluable time marker in European sediments with increasing importance because it occurs just before the onset of the Younger Dryas (YD) cold event. As the YD begins ca. 200 calendar years after the LST was deposited, accurate determination of the radiocarbon age of this ash layer will lead to a more accurate age assignment for the beginning of the YD. On the basis of 12 terrestrial plant macrofossil 14C ages derived from sediments from Soppensee, Holzmaar and Schlakenmehrener Maar, we found an age of at least 11,230 +/40 BP for the LST event. This is ca. 200 yr older than the often reported age of 11,000 +/50 BP (van den Bogaard and Schmincke 1985).
    • Radiocarbon Calibration and Analysis of Stratigraphy: The OxCal Program

      Bronk Ramsey, Christopher (Department of Geosciences, The University of Arizona, 1995-01-01)
      People usually study the chronologies of archaeological sites and geological sequences using many different kinds of evidence, taking into account calibrated radiocarbon dates, other dating methods and stratigraphic information. Many individual case studies demonstrate the value of using statistical methods to combine these different types of information. I have developed a computer program, OxCal, running under Windows 3.1 (for IBM PCs), that will perform both 14C calibration and calculate what extra information can be gained from stratigraphic evidence. The program can perform automatic wiggle matches and calculate probability distributions for samples in sequences and phases. The program is written in C++ and uses Bayesian statistics and Gibbs sampling for the calculations. The program is very easy to use, both for simple calibration and complex site analysis, and will produce graphical output from virtually any printer.
    • A Note Concerning "Location-Dependent Differences in the 14C Content of Wood" by McCormac et al

      Damon, Paul E. (Department of Geosciences, The University of Arizona, 1995-01-01)
    • A Comparative Study of Monsoonal and Non-Monsoonal Himalayan Lakes, India

      Kusumgar, Sheela; Agrawal, D. P.; Deshpande, R. D.; Ramesh, Rengaswamy; Sharma, C.; Yadava, M. G. (Department of Geosciences, The University of Arizona, 1995-01-01)
      Sedimentological, mineral magnetic and carbon isotopic studies on cores from Mansar Lake in the Jammu area provide paleomonsoonal history dating back to 580 BC. From ca. 580 BC to AD 300, the region experienced precipitation similar to the present, whereas from AD 300 to 1400, the monsoon was relatively subdued. A small excursion ca. AD 1100 suggests an effect of medieval warming. Studies in the Kumaon region did not provide a proper precipitation record, as anthropogenic activity interfered with sedimentation. Manasbal Lake in Kashmir gave an inversion of 14C chronology due to younger paleosols in the drainage basin. Further, the episodic nature of sedimentation in Manasbal Lake hampered the reconstruction of precipitation history in the area.
    • A Computer-Based Database for Radiocarbon Dates of Central Andean Archaeology

      Michczyński, Adam; Krzanowski, Andrzej; Pazdur, Mieczysław F.; Ziołkowski, Mariusz S. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We established a database of 14C dates from archaeological sites of the Central Andes region of Peru, Ecuador and Bolivia on an IBM PC-compatible microcomputer running on an MS-DOS operating system using software package dBASE IV, version 1.1. Relevant data are stored in three DBF-type database files. The file ANDY.DBF contains information on dates and samples; REFERENC.DBF contains references to relevant publications and CALAND.DBF contains calibrated dates. The total number of records of the ANDY database slightly exceeds 2650.
    • A Method for Quantifying Deep-Sea Carbonate Dissolution Using 14C Dating

      van Kreveld, S. A.; Ganssen, G. M.; van der Plicht, J. E.; Melkert, M. M.; Troelstra, S. R.; van der Borg, K.; de Jong, Arie (Department of Geosciences, The University of Arizona, 1995-01-01)
      We quantified the rate of carbonate dissolution with increasing water depth by taking the difference in the carbonate mass accumulation rate of deep (3393-4375 m) core top sediments from the shallowest one (3208 m), which we assumed was unaffected by dissolution. This method depends on high quality 14C dates that we calibrated to calendar years for calculating sedimentation rates. Our results show low (ranging from 0 to 0.3 g cm-2 ka-1) and high (ranging from 1.5 to 1.7 g cm-2 ka-1) carbonate dissolution rates, above and below 4000 m, respectively. Therefore, we interpret the sudden increase in the carbonate dissolution rate at 4000-m water depth to mark the lysocline.
    • A Data Acquisition System for Proportional Counters at Gliwice

      Michczyński, Adam; Goslar, Tomasz; Pazdur, Anna; Pazdur, Mieczysfaw F. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We present here the principal ideas of a new, fully computerized data acquisition system with pulse-rise background reduction, developed in the Gliwice Radiocarbon Laboratory, and our first results. The new system uses a microprocessor-controlled pulse and coincidence analyzer for acquisition of data from 3 of 4 proportional counter sets. The analyzer acquires and stores information on the pulse's amplitudes and rise-times and their coincidence with guard counters and radiofrequency shield. This feature allows us to separate pulses using anticoincidence information and pulse-shape discrimination. The described method of background reduction led to a significant increase in the factor of merit on 2 of 3 counters tested.
    • A General Computer Program for Radiocarbon Dating Laboratories

      González-Gómez, Cecilio (Department of Geosciences, The University of Arizona, 1995-01-01)
      Radiocarbon dating laboratories deal with many types of data and calculations, which include information on received and dated samples, age calculations and storage of results, printed reports to submitters and graphs plotted from sample measurements. I describe a computer program, designed to run on any PC-compatible computer with a hard disk, that can handle all the functions of a conventional liquid scintillation counting radiocarbon dating laboratory.
    • A Correction for In-Situ 14C in Antarctic Ice with 14CO

      van Roijen, Job; van der Borg, Klaas; de Jong, Arie; Oerlemans, Johannes (Department of Geosciences, The University of Arizona, 1995-01-01)
      We use a dry extraction method to obtain trapped CO2 of shallow ice cores from a blue ice area of East Antarctica. In-situ-produced 14C extracted in 14CO2 and 14CO concentrations show a mean ratio of 3.4 +/0.4. Correction for insitu 14CO2 resulted in ice ages within 7-13 ka. The accumulation and ablation rates determined from the in-situ production of 7-20 cm yr-1 and 10-13 cm yr-1, respectively, agree with field measurements, and thus indicate close to total efficiency of extraction.
    • A Comparison of Marine and Terrestrial Radiocarbon Ages from Northern Chile

      Southon, John R.; Oakland Rodman, Amy; True, Delbert (Department of Geosciences, The University of Arizona, 1995-01-01)
      The calibration of radiocarbon dates on marine materials involves a global marine calibration with regional corrections. Data from well-associated marine and terrestrial materials in archaeological artifacts from northern Chile indicated that the calibration is valid for the period AD 200-900 and suggest that coastal upwelling intensities during that period were similar to those of the early 20th century.
    • Radiocarbon Dating of Shells and Foraminifera from the Skagen Core, Denmark: Evidence of Reworking

      Heier-Nielsen, Susanne; Conradsen, Keld; Heinemeier, Jan; Knudsen, K. L.; Nielsen, H. L.; Rud, Niels; Sveinbjörnsdóttir, Á. E. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We report on 69 radiocarbon dates of mollusk shells and benthic foraminifera from the upper 132 m of the marine shelf sediments of the Skagen Core (220 m total length). The dated sequence covers the Late Glacial and the Holocene (from 15 ka BP to Recent). Sedimentation rates range from 1 to 70 m ka-1. The macrofossil shell dates follow a smooth curve constituting an age model for dating the sediments. The foraminiferal dates fall into two groups: those that agree exactly with the mollusk shells and those that deviate substantially, always being older than the shells by as much as 5 ka. One mixed foraminiferal sample consisted of members from both groups, and as a result, the age deviation of the sample turned out to be some weighted average. The data indicate that the age deviations are due to admixtures of reworked older foraminifera.
    • AMS 14C Measurements of Dissolved Inorganic Carbon in Pore Waters from a Deep-Sea "Cold Seep" Giant Clam Community Off Hatsushima Island, Sagami Bay, Japan

      Masuzawa, Toshiyuki; Kitagawa, Hiroyuki; Nakatsuka, Takeshi; Handa, Nobuhiko; Nakamura, Toshio (Department of Geosciences, The University of Arizona, 1995-01-01)
      We collected pore waters using an in situ pore water-squeezer for a submersible Shinkai 2000 at six depths beneath the sediment surface within a deep-sea "cold seep" giant clam community off Hatsushima Island, Sagami Bay, Japan. A box core sample was also collected ca. 4.5 km east of the community and pore waters were separated. Dissolved inorganic carbon (DIC) was extracted and purified in a vacuum line and 14C concentration was determined with a Tandetron accelerator mass spectrometer at Nagoya University after conversion to graphite targets using a batch Fe-catalytic hydrogen reduction method. Delta-14C values decreased with increasing depth to -938 per mil at the sulfate concentration minimum. This indicates that methane used for the active reduction of sulfate and formation of hydrogen sulfide, which is used by symbiotic chemoautotrophic bacteria in gills of the giant clams, is almost dead and is likely supplied from the deep. delta-14C values of DIC vary linearly with delta-13C values along a mixing line between that in the bottom water and that produced by the oxidation of dead methane. The delta-13C value of DIC oxidized from dead methane is estimated to be ca. -45 per mil.
    • AMS 14C Dating of Varved Sediments from Lake Suigetsu, Central Japan and Atmospheric 14C Change During the Late Pleistocene

      Kitagawa, Hiroyuki; Fukuzawa, Hitoshi; Nakamura, Toshio; Okamura, Makoto; Takemura, Keiji; Hayashida, Akira; Yasuda, Yoshinori (Department of Geosciences, The University of Arizona, 1995-01-01)
      We made accelerator mass spectrometry (AMS) 14C measurements on terrestrial macrofossils from the Late Pleistocene/Holocene of the annually laminated sediments of Lake Suigetsu (central Japan). The AMS 14C dates of terrestrial macrofossils showed agreement between varve counting years and calibrated ages (tree rings and U/Th on coral) in the interval of 10.5 and ca. 11.5 ka cal BP. Beyond 11.5 ka cal BP, the age difference between 14C and varve counting years gradually diminish, contradicting published data on corals dated by U/Th and 14C.
    • 1996 Price List

      Department of Geosciences, The University of Arizona, 1995-01-01
    • Radiocarbon Dating of Prehistoric Shell from New Zealand and Calculation of the Delta-R Value Using Fish Otoliths

      Higham, Thomas F. G.; Hogg, A. G. (Department of Geosciences, The University of Arizona, 1995-01-01)
      We calculated a new Delta-R for New Zealand waters using 14C dates of historic shell previously presented by McFadgen and Manning (1990), and fish otoliths dated by Kalish (1993). We obtained a new estimate of -25 +/15 14C yr. To test the accuracy of this value for correcting conventional 14C marine ages, we dated shell of a variety of different species excavated at the prehistoric site of Shag Mouth, North Otago. We compared the results with a pooled mean date for terrestrial samples and calculated a local AR value that we found statistically indistinguishable from the new Delta-R estimate for New Zealand.