• Marine Radiocarbon Reservoir Corrections for the Mediterranean and Aegean Seas

      Reimer, P. J.; McCormac, F. G. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Radiocarbon measurements of nine known age shells from the Mediterranean and the Aegean Seas combined with previous measurements provide an updated value for Delta-R, the local variation in the reservior correction for marine samples. Comparison of pre-1950s samples from the Algerian coast, with one collected in 1954, indicates early incorporations of nuclear weapons testing 14C into the shallow surface waters of the Mediterranean. Comparisons between different basins indicate the surface waters of the Mediterranean are relatively homogenous. The recommended Delta-R for calibration of the Mediterranean marine samples with the 1998 marine calibration dataset is 58 +/85 14C yr, but variations in the resevoir age beyond 6000 cal BP should be considered.
    • Marine Reservoir Corrections for the Indian Ocean and Southeast Asia

      Southon, John; Kashgarian, Michaele; Fontugne, Michel; Metivier, Bernard; Yim, Wyss W-S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We have measured radiocarbon in prebomb known-age shells and coral from the Indian Ocean and southeast Asia to determine marine reservoir age corrections. Western Indian Ocean results show a strong 14C depletion due to upwelling in the Arabian Sea, and indicate that this signal is advected over a wide area to the east and south. In contrast, the surface waters of the South China Sea contain relatively high levels of 14C, due in part to the input of well-equilibrated water masses from the western Pacific. The easternmost regions of the Indian Ocean are also strongly influenced by the flowthrough of Pacific waters north of Australia.
    • Novel Statistical Model for a Piece-Wise Linear Radiocarbon Calibration Curve

      Gómez Portugal Aguilar, Delil; Litton, Cliff D.; O'Hagan, Anthony (Department of Geosciences, The University of Arizona, 2002-01-01)
      The process of calibrating radiocarbon determinations onto the calendar scale requires the setting of a specific statistical model for the calibration curve. This model specification will bear fundamental importance for the resulting inference regarding the parameter of interest—namely, in general, the calendar age associated to the sample that has been 14C-dated. Traditionally, the 14C calibration curve has been modelled simply as the piece-wise linear curve joining the (internationally agreed) high-precision calibration data points; or, less frequently, by proposing spline functions in order to obtain a smoother curve. We present a model for the 14C calibration curve which, based on specific characteristics of the dating method, yields a piece-wise linear curve, but one which rather than interpolating the data points, smooths them. We show that with this specific model if a piece-wise linear curve is desired, an underlying random walk model is implied as covariance structure (and vice versa). Furthermore, by making use of all the information provided by the calibration data in a comprehensive way, we achieve an improvement over current models by getting more realistic variance values for the calibration curve.
    • Radiocarbon and Stable Isotope Analyses of Archaeological Bone Consolidated with Hide Glue

      Takahashi, C. M.; Nelson, D. E.; Southon, J. S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We tested a simple method for removing a collagen-based glue preservative from bone destined for radiocarbon and stable isotope analyses. The method is sufficient for bone samples from which only stable isotope measurements are required. For 14C dating, such samples of age less than about 10 ka can be adequately dated, but for older samples, the circumstances must be carefully evaluated.
    • Radiocarbon Dating of Buried Holocene Soils in Siberia

      Orlova, Lyubov A.; Zykina, Valentina S. (Department of Geosciences, The University of Arizona, 2002-01-01)
      We have constructed a detailed chronological description of soil formation and its environments with data obtained on radiocarbon ages, palynology, and pedology of the Holocene buried soils in the forest steppe of western and central Siberia. We studied a number of Holocene sections, which were located in different geomorphic situations. Radiocarbon dating of materials from several soil horizons, including soil organic matter (SOM), wood, peat, charcoal, and carbonates, revealed three climatic periods and five stages of soil formation in the second part of the Holocene. 14C ages of approximately 6355 BP, 6020 BP, and 5930 BP showed that the longest and most active stage is associated with the Holocene Climatic Optimum, when dark-grey soils were formed in the forest environment. The conditions of birch forest steppe favored formation of chernozem and associated meadow-chernozem and meadow soils. Subboreal time includes two stages of soil formation corresponding to lake regressions, which were less intense than those of the Holocene Optimum. The soils of that time are chernozem, grassland-chernozem, and saline types, interbedded with thin peat layers 14C dated to around 4555 BP, 4240 BP and 3480 BP, and 3170 BP. Subatlantic time includes two poorly developed hydromorphic paleosols formed within inshore parts of lakes and chernozem-type automorphic paleosol. The older horizon was formed during approximately 2500-1770 BP, and the younger one during approximately 1640-400 BP. The buried soils of the Subatlantic time period also attest to short episodes of lake regression. The climate changes show an evident trend: in the second part of the Atlantic time period it was warmer and drier than at present, and in the Subboreal and Subatlantic time periods the climate was cool and humid.
    • Radiocarbon, Volume 44, Number 1 (2002)

      Department of Geosciences, The University of Arizona, 2002-01-01
    • Reservoir Corrections for Marine Samples from the South Atlantic Coast, Santa Catarina State, Brazil

      Eastoe, C. J.; Fish, S.; Fish, P.; Gaspar, M. Dulce; Long, A. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Coeval shell and charcoal from Santa Catarina State, Brazil, differ systematically in 14C content, indicating a reservoir effect in marine samples. For modern samples (AD 1939-2000) and archeological samples (2500-1595 BP), the mean 14C age difference between marine and atmospheric carbon is 220 +/20 years, the marine carbon being older. For three samples dated AD 1939-1944, a distinct reservoir correction of 510 +/10 years is also observed. The ages of archeological shell samples from Jabuticabeira may be corrected by subtracting 220 years from the apparent 14C ages.
    • Soil Organic Matter Decomposition and Turnover in a Tropical Ultisol: Evidence from delta-13C, delta-15N and Geochemistry

      Krull, Evelyn S.; Bestland, Erick A.; Gates, Will P. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (delta-13C) and nitrogen (delta-15N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of delta-13C and delta-15N showed a distinct enrichment trend down profile with a large (average 13Delta-C = 5.0 per mil average 15Delta-N = 6.3 per mil) and abrupt offset within the uppermost 10-20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 per mil are usually interpreted as a recent change from C4 to C3 dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.
    • The Use of Raman Spectroscopy to Monitor the Removal of Humic Substances from Charcoal: Quality Control for 14C Dating of Charcoal

      Alon, Dani; Mintz, Genia; Cohen, Illit; Weiner, Steve; Boaretto, Elisabetta (Department of Geosciences, The University of Arizona, 2002-01-01)
      One of the largest sources of uncertainty in radiocarbon dating stems from the sample pretreatment procedures used to minimize contamination. A major source of carbon contamination in charcoal from archaeological sites is humic substances carried by groundwater. Here we present a method, independent of 14C dating itself, to evaluate the effectiveness of the cleaning procedure of charcoal. Raman spectra of mixtures of humic substances (HS) and laboratory prepared charcoal indicate that Raman spectroscopy can be used as a semi-quantitative measure of the amount of humic substances associated with archaeological charcoal. Raman spectral analysis of archaeological charcoal samples subjected to different cleaning regimes supports this contention. Such measurements can provide quality control for charcoal preparation procedures and may assist in the interpretation of carbon-dating results.
    • Why Early-Historical Radiocarbon Dates Downwind from the Mediterranean are Too Early

      Keenan, Douglas J. (Department of Geosciences, The University of Arizona, 2002-01-01)
      Several authors have claimed that radiocarbon dates in the Ancient Near East are too early. Herein, a hypothesis that might explain this is presented. Marine degassing of "old" carbon (i.e. 14C-deficient C), induced by upwelling of old subsurface water, has been observed, n modern times, to cause century-scale 14C ages in the surface atmosphere. A review of the Mediterranean Sea post-ice-age circulation concludes that the subsurface waters became very old, primarily due to millennia-long stagnation. It is hypothesized that as the stagnation ended, subsurface waters were brought towards the surface, where they degassed old carbon. Additionally, Anatolian dendrochronology is shown to not contradict the hypothesis.
    • WOCE Radiocarbon IV: Pacific Ocean Results; P10, P13N, P14C, P18, P19 & S4P

      Key, Robert M.; Quay, Paul D.; Schlosser, Peter; McNichol, A. P.; von Reden, K. F.; Schneider, Robert J.; Elder, Kathy L.; Stuiver, Minze; Östlund, H. Göte (Department of Geosciences, The University of Arizona, 2002-01-01)
      The World Ocean Circulation Experiment, carried out between 1990 and 1997, provided the most comprehensive oceanic study of radiocarbon to date. Approximately 10,000 samples were collected in the Pacific Ocean by U.S. Investigators for both conventional large volume B counting and small volume accelerator mass spectrometry analysis techniques. Results from six cruises are presented. The data quality is as good or better than previous large-scale surveys. The 14C distribution for the entire WOCE Pacific data set is graphically described using mean vertical profiles and sections, and property-property plots.