• Radiocarbon, Volume 47, Number 1 (2005)

      Department of Geosciences, The University of Arizona, 2005-01-01
    • Pre-Bomb Δ14C Variability and the Suess Effect in Cariaco Basin Surface Waters as Recorded in Hermatypic Corals

      Guilderson, Thomas P.; Cole, Julia E.; Southon, John R. (Department of Geosciences, The University of Arizona, 2005-01-01)
      The Delta-14C content of surface waters in and around the Cariaco Basin was reconstructed from radiocarbon measurements on sub-annually sampled coral skeletal material. During the late 1930s to early 1940s, surface waters within and outside of the Cariaco Basin were similar. Within the Cariaco Basin at Islas Tortugas, coral Delta-14C averages -51.9 +/3.3ppm. Corals collected outside of the basin at Boca de Medio and Los Testigos have Delta-14C values of -53.4 +/3.3ppm and -54.3 +/2.6, respectively. Additional 14C analyses on the Isla Tortugas coral document an ~11 decrease between ~1905 (-40.9 +/4.5ppm) and ~1940. The implied Suess effect trend (-3ppm/decade) is nearly as large as that observed in the atmosphere over the same time period. If we assume that there is little to no fossil fuel 14CO2 signature in Cariaco surface waters in ~1905, the waters have an equivalent reservoir age of ~312 yr.
    • Radiocarbon Dating of Modern Peat Profiles: Pre- and Post-Bomb 14C Variations in the Construction of Age-Depth Models

      Goslar, Tomasz; van der Knaap, W. O.; Hicks, Sheila; Andrič, Maja; Czernik, Justyna; Goslar, Ewa; Räsänen, Satu; Hyötylä, Heidi (Department of Geosciences, The University of Arizona, 2005-01-01)
      We present studies of 9 modern (up to 400-yr-old) peat sections from Slovenia, Switzerland, Austria, Italy, and Finland. Precise radiocarbon dating of modern samples is possible due to the large bomb peak of atmospheric 14C concentration in 1963 and the following rapid decline in the 14C level. All the analyzed 14C profiles appeared concordant with the shape of the bomb peak of atmospheric 14C concentration, integrated over some time interval with a length specific to the peat section. In the peat layers covered by the bomb peak, calendar ages of individual peat samples could be determined almost immediately, with an accuracy of 2-3 yr. In the pre-bomb sections, the calendar ages of individual dated samples are determined in the form of multi-modal probability distributions of about 300 yr wide (about AD 1650-1950). However, simultaneous use of the post-bomb and pre-bomb 14C dates, and lithological information, enabled the rejection of most modes of probability distributions in the pre-bomb section. In effect, precise age-depth models of the post-bomb sections have been extended back in time, into the "wiggly" part of the 14C calibration curve. Our study has demonstrated that where annual resolution is concerned, tissues of Sphagnum are the only representative material for 14C dating, although even samples of pure Sphagnum collected from a very thin slice of the peat section contain tissues grown in different years, so they integrate the atmospheric 14C signal over a period of time. This time period (0.5-8 yr, depending on the site) seems to correlate with the peat accumulation rate, but it also depends on how the sampled peat sections were handled. When constructing age-depth models, for some peat sections we used the strategy of multi-stage 14C dating. This led to a drastic reduction in the uncertainty of the age-depth models, by dating only a few additional samples in the profile. Our study is the first in which peat sections from the late pre-bomb time (AD 1900-1960) have been precisely dated at a high temporal resolution. In this time interval, 14C ages of all the samples dated were younger than those derived from the atmospheric ccalibration curve, apparently due to the effect of integration. Evidently, the determination of calendar ages based on 14C dating of single peat examples from that interval may be affected by a serious error if the possibility of integration is ignored.
    • Radiocarbon Updates

      Department of Geosciences, The University of Arizona, 2005-01-01
      Software Updates, Upcoming Conferences
    • Blank Correction for Δ14C Measurements in Organic Compound Classes of Oceanic Particulate Matter

      Hwang, Jeomshik; Druffel, Ellen R. M. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Contaminant carbon (blank carbon) was studied for its impact on the carbon isotope measurements (Delta-14C and delta-13C) of 3 organic compound classes of oceanic particulate organic matter. Two methods of blank correction and associated uncertainties were studied. First, the carbon blanks were quantified manometrically and the isotope ratios of the blank carbon were measured directly. Second, the isotope ratios of the blank carbon were estimated using the standard dilution method from the difference in Delta-14C values between unprocessed and processed standards. The 2 methods agreed within the uncertainties. The standard deviations of numerous Delta-14C measurements made on processed standard compounds were comparable to those of real samples. Blank correction using the standard dilution method is much less sensitive to the error in determination of blank carbon mass than is correction using the directly measured mass and Delta-14C values of the blank carbon. The standard dilution method is recommended for correcting Delta-14C analyses of small samples that involve incorporation of a significant amount of blank carbon.
    • New Bomb Pulse Radiocarbon Records from Annual Tree Rings in the Northern Hemisphere Temperate Region

      Quarta, G.; D'Elia, M.; Valzano, D.; Calcagnile, L. (Department of Geosciences, The University of Arizona, 2005-01-01)
      The bomb radiocarbon spike induced by atmospheric nuclear detonations has been reconstructed at a latitude of 40 degrees N by measuring the 14C content in annual rings of a living pine (Pinus pinea) at the Accelerator Mass Spectrometry facility of the University of Lecce. We report how the samples were taken, selected, prepared for analysis, and measured. The results are in good agreement with other data sets available for the Northern Hemisphere temperate regions, showing that a curve for the calibration of 14C dates, valid for the whole Northern Hemisphere, can be established for the second half of the 20th century.
    • The Stratigraphic Sequence at Yalâ (Yemen): A Statistical Evaluation

      Manzo, Andrea (Department of Geosciences, The University of Arizona, 2005-01-01)
      The South Arabian chronology has been problematic for a long time and this is also a true vexata quaestio for the ancient history of South Arabia. Three different chronologies have been suggested for the first literate phase of South Arabian cultures, which may date to the 11th century BC, the late 8th century BC, or the 5th century BC (see de Maigret 1996:157-63; de Maigret and Robin 1989: 276-8; Pirenne 1988; Robin 1997; Figure 1). At the site of Yal, potsherds with incised South Arabian inscriptions have been recovered in a stratum dating at least to the 8th century BC, if not earlier, and offer evidence of the existence of South Arabian culture at that time (de Maigret and Robin 1989:288-9).
    • AMS Radiocarbon Dating of Bone Samples from the Xinzhai Site in China

      Liu, Kexin; Han, Baoxi; Guo, Zhiyu; Wu, Xiaohong; Yuan, Sixun; Kutschera, Walter; Ma, Hongji; Priller, Alfred; Steier, Peter; Wild, Eva Maria; et al. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Xinzhai is an important archaeological site discovered 40 yr ago and recently re-excavated in the Henan Province, dynasty of China. Radiocarbon measurements on bone samples from this site were performed at the Peking University AMS facility (PKU-AMS) and the Vienna University AMS facility (VERA). Calibrated ages were obtained with the computer program OxCal. The results of these measurements are presented and the related chronology is discussed.
    • Chronologies for Recent Peat Deposits Using Wiggle-Matched Radiocarbon Ages: Problems with Old Carbon Contamination

      Charman, Dan J.; Garnett, Mark H. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Dating sediments which have accumulated over the last few hundred years is critical to the calibration of longer-term paleoclimate records with instrumental climate data. We attempted to use wiggle-matched radiocarbon ages to date 2 peat profiles from northern England which have high-resolution records of paleomoisture variability over the last ~300 yr. A total of 65 14C accelerator mass spectrometry (AMS) measurements were made on 33 macrofossil samples. A number of the age estimates were older than expected and some of the oldest ages occurred in the upper parts of the sequence, which had been dated to the late 19th and early 20th century using other techniques. We suggest that the older 14C ages are the result of contamination by industrial pollution. Based on counts of spheroidal carbonaceous particles (SCPs), the potential aging effect for SCP carbon was calculated and shown to be appreciable for samples from the early 20th century. Ages corrected for this effect were still too old in some cases, which could be a result of fossil CO2 fixation, non-SCP particulate carbon, contamination due to imperfect cleaning of samples, or the reservoir effect from fixation of fossil carbon emanating from deeper peat layers. Wiggle matches based on the overall shape of the depth-14C relationship and the 14C minima in the calibration curve could still be identified. These were tested against other age estimates (210Pb, pollen, and SCPs) to provide new age-depth models for the profiles. New approaches are needed to measure the impact of industrially derived carbon on recent sediment ages to provide more secure chronologies over the last few hundred years.
    • Reassessing Human Settlement on the South Coast of San Miguel Island, California: The Use of 14C Dating as a Reconnaissance Tool

      Braje, Todd J.; Erlandson, Jon M.; Rick, Torben C. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Californias San Miguel Island contains over 600 archaeological sites, some occupied as early as 12,000 yr ago and most located along the islands north coast. Archaeologists have long believed the south coast to have been marginal or largely uninhabited. Burial of some landforms by sand dunes deposited after historical overgrazing, the lack of systematic survey, and a dearth of radiocarbon dating have also contributed to an underestimation of the intensity of human land use along the south coast of San Miguel Island. Our recent reconnaissance and dating of shell middens on the islands south coast indicate more intensive occupation than previously thought, with numerous south coast sites spanning at least the past 9000 yr, and demonstrate the utility of combining systematic archaeological reconnaissance and radiometrics in reconstructions of human settlement and historical ecology in coastal environments.
    • Dating the Iron Age I/II Transition in Israel: First Intercomparison Results

      Boaretto, Elisabetta; Jull, A. J. Timothy; Gilboa, Ayelet; Sharon, Ilan (Department of Geosciences, The University of Arizona, 2005-01-01)
      Nearly a decade ago, a different chronology than the conventional absolute chronology for the early Iron Age in Israel was suggested. The new, lower chronology transfers Iron Age I and Iron Age IIA contexts in Israel, traditionally dated to the 11th and 10th centuries BCE, to the 10th and 9th centuries, respectively. Thus, it places the Iron I/IIA transition at about 920-900 BCE. This alternative chronology carries important implications for Israelite history, historiography, and Bible research, as well as for the chronologies of other regions around the Mediterranean. Relevant radiocarbon data sets published to date, which were measured at different sites by different laboratories, were claimed to be incompatible. Therefore, the question of agreement between laboratories and dating methods needs to be addressed at the outset of any study attempting to resolve such a tight chronological dilemma. This paper addresses results pertaining to this issue as part of a comprehensive attempt to date the early Iron Age in Israel based on many sites, employing different measuring techniques in 2 laboratories. The intercomparison results demonstrate that: a) the agreement between the 2 laboratories is well within the standard in the 14C community and that no bias can be detected in either laboratory; and b) calculating the Iron I|IIa transition in 3 different ways (twice independently by the measurements obtained at the 2 labs and then by combining the dates of both) indicates that the lower chronology is the preferable one.
    • Radiocarbon Dates from Soil Profiles in the Teotihuacán Valley, Mexico: Indicators of Geomorphological Processes

      De Tapia, Emily McClung; Rubio, Irma Domínguez; Castro, Jorge Gama; Solleiro, Elizabeth; Sedov, Sergey (Department of Geosciences, The University of Arizona, 2005-01-01)
      Radiocarbon dates largely obtained from bulk soil samples in 24 soil profiles in the Teotihuacán Valley, Mexico, are reported insofar as they represent a first step towards developing a sequence of soil formation, erosion, vegetation change, and human impact during the Holocene. Limitations of 14C dating in the area are considered, particularly the absence of charcoal in sediments and poor preservation of pollen. A broad temporal scheme is proposed to guide future research in which 4 periods are defined: ~5000-2000 BP (relative stability with short, intermittent episodes of erosion); ~2000-1500 BP (erosion-sedimentation, deforestation, and intensive agriculture); ~1500-1000 BP (relative stability, depopulation, and partial recovery of the landscape); and ~1000-500 BP (erosion-sedimentation, deforestation, and intensive agriculture).
    • A Simple, Extremely Stable Single-Tube Liquid Scintillation System for Radiocarbon Dating

      Theodórsson, Páll (Department of Geosciences, The University of Arizona, 2005-01-01)
      This paper describes a simple and compact liquid scintillation radiocarbon dating system, ICELS, and demonstrates its long-term stability and reproducibility to a precision level rarely presented before, better than 0.04% (3 14C yr). Inexpensive systems of this kind may, in the future, help to meet increasing demand for high precision (+/16 to +/20 14C yr) and strict quality control. ICELS comprises a compact detector unit, where a 3-mL dome-shaped vial, with an optimal light reflector, sits on the top of a vertical 30-mm photomultiplier tube. Sample changing is manual. The high voltage is set at the balance point for each sample, securing maximal counting stability. The quench correction method used (spectrum restoration) corrects with 0.04% precision for all parameters that can normally shift the 14C spectrum. For 3 mL of benzene at 71% 14C counting efficiency (recent carbon 23 cpm), the background is 1.72 cpm behind a 5-cm-thick shield of lead (27 kg) and 1.53 cpm behind 10 cm of lead. The background count rate corrected for atmospheric pressure variations was completely stable over 47and 57-d testing periods for the 2 systems.
    • Estimating Turnover of Soil Organic Carbon Fractions Based on Radiocarbon Measurements

      Bruun, Sander; Six, Johan; Jensen, Lars S.; Paustian, Keith (Department of Geosciences, The University of Arizona, 2005-01-01)
      In this paper, we examine 3 different models used to estimate turnover of soil organic carbon (SOC) fractions using radiocarbon measurements: one conventional carbon dating model and two bomb 14C models. One of the bomb 14C models uses an atmospheric 14C record for the period 22,050 BC to AD 2003 and is solved by numerical methods, while the other assumes a constant 14C content of the atmosphere and is solved analytically. The estimates of SOC turnover obtained by the conventional 14C dating model differed substantially from those obtained by the bomb 14C models, which we attribute to the simplifying assumption of the conventional 14C model that the whole SOC fraction is of the same age. The assumptions underlying the bomb 14C models are more applicable to SOC fractions; therefore, the calculated turnover times are considered to be more reliable. We used Monte Carlo simulations to estimate the uncertainties of the turnover times calculated with the numerically solved 14C model, accounting not only for measurement errors but also for uncertainties introduced from assumptions of constant input and uncertainties in the 14C content of the CO2 assimilated by plants. The resulting uncertainties depend on systematic deviations in the atmospheric 14C record for SOC fractions with a fast turnover. Therefore, the use of the bomb 14C models can be problematic when SOC fractions with a fast turnover are analyzed, whereas the relative uncertainty of the turnover estimates turned out to be smaller than 30% when the turnover time of the SOC fractions analyzed was longer than 30 yr, and smaller than 15% when the turnover time was longer than 100 yr.
    • Reservoir Effect of the Southern and Southeastern Brazilian Coast

      Angulo, Rodolfo J.; de Souza, Maria C.; Reimer, Paula J.; Sasaoka, Sueli K. (Department of Geosciences, The University of Arizona, 2005-01-01)
      A regional marine reservoir correction (Delta-R) of 33 +/24 14C yr for southern Brazil was obtained from 6 marine shell samples collected in the states of Santa Catarina and Paran. This work also presents a R estimation of 8 +/17 14C yr for the southern and southeastern Brazilian coast from the states of Rio de Janeiro to Santa Catarina, obtained by including 7 ages published in previous works. The high variability of R in modern and Holocene samples from the Brazilian coast is also discussed.
    • Reconstruction of the 14C Production Rate from Measured Relative Abundance

      Usoskin, Ilya G.; Kromer, Bernd (Department of Geosciences, The University of Arizona, 2005-01-01)
      A new method is presented for the reconstruction of the radiocarbon production rate from the measured relative abundance of ∆14C. The method treats the carbon cycle as a linear Fourier filter and thus allows for the correct and unambiguous inversion of the carbon cycle. The 14C production rate, as reconstructed by the Fourier filter method, agrees with the results obtained by the traditional iteration method. Since the 2 methods use completely different approaches, this verifies the validity of the reconstruction. The composite series is presented, based on both methods and their systematic uncertainties.
    • Comparative Radiocarbon Dating of Lignite, Pottery, and Charcoal Samples from Babeldaob Island, Republic of Palau

      Anderson, Atholl; Chappell, John; Clark, Geoffrey; Phear, Sarah (Department of Geosciences, The University of Arizona, 2005-01-01)
      It is difficult to construct archaeological chronologies for Babeldaob, the main island of Palau (western Micronesia), because the saprolitic clays of the dominant terraced-hill sites and associated ceramic sherds often contain old carbon that originated in lignites. This has implications, as well, for chronologies of sedimentary sequences. Comparative analysis of the dating problem using lignite, pottery, and charcoal samples indicates that, in fact, there are both old and young sources of potential contamination. It is concluded that radiocarbon samples from Babeldaob need to be tested for appropriate carbon content rather than relying solely upon material identification.
    • Improved Tube Cracker for Opening Vacuum-Sealed Glass Tubes

      Norton, Glenn A. (Department of Geosciences, The University of Arizona, 2005-01-01)
      A variety of analytical procedures involve breaking open a glass or quartz vessel containing a gaseous sample, and then quantitatively collecting the sample gases for analysis. In order to do this, a variety of "tube crackers" have been used. This paper discusses an alternate tube cracker that offers numerous advantages over those that have been discussed previously in the literature.