• Atmospheric 14C Variability Recorded in Tree Rings from Peninsular India: Implications for Fossil Fuel CO2 Emission and Atmospheric Transport

      Chakraborty, Supriyo; Dutta, Koushik; Bhattacharyya, Amalava; Nigam, Mohit; Schuur, Edward AG; Shah, Santosh K. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Radiocarbon analysis in annual rings of a teak tree (Tectona grandis) is reported in comparison with previously published results. Samples (disks) were collected from Hoshangabad (22 degrees 30'N, 78 degrees E), Madhya Pradesh, in central India. The previously published sample was collected from Thane (19 degrees 12'N, 73 degrees E), Maharashtra, near the west coast of India (Chakraborty et al. 1994). Two short 14C time series were reconstructed with these tree samples to capture the bomb peak of atmospheric 14C and the spatial variability in this record. These time series represent the periods 1954-1977 and 1959-1980 for Hoshangabad and Thane, respectively. The 14C peaks in these places appear around 1964-1965. The Hoshangabad tree records a peak delta-14C value of 708 +/- 8‰, which conforms to the peak value of Northern Hemisphere Zone 3 as described in Hua and Barbetti (2004). But the peak 14C at Thane is somewhat less (630 +/- 8‰) probably due to the dilution by fossil fuel CO2 free of 14C emanating from the neighboring industrial areas. This depletion of peak values has been used to estimate the local emission of fossil fuel CO2, which is approximately 2.3% of the background atmospheric CO2 concentration.
    • AMS Radiocarbon Dating of Wood Samples from the Angkor Monuments, Cambodia

      Uchida, E.; Cunin, O.; Shimoda, I.; Takubo, Y.; Nakagawa, T. (Department of Geosciences, The University of Arizona, 2008-01-01)
      In the Angkor monuments of Cambodia, pieces of wood remain (as head frames of doorways, crossbeams, ceiling boards, etc.) in the following 8 monuments: Bakong, Lolei, Baksei Chamkrong, North Khleang, Angkor Wat, Banteay Kdei, Bayon, and Gates of Angkor Thom. Accelerator mass spectrometry (AMS) radiocarbon dating carried out on 15 wood samples collected from the above 8 monuments revealed that most of the wood samples are original, except for the head frame of a doorway in Baksei Chamkrong, the ceiling boards in the northwest tower, and a crossbeam with pivot hole in the southwest tower of the Inner Gallery of Angkor Wat. The 14C age for the head frame of a doorway in the inner wall under the central tower of North Khleang supports the hypothesis that the inner walls are additions from a later period.
    • Age Discrepancies with the Radiocarbon Dating of Sagebrush (Artemisia Tridentata Nutt.)

      Geib, Phil R. (Department of Geosciences, The University of Arizona, 2008-01-01)
      When ancient hearths at open archaeological sites do not yield carbonized annual plant remains or other high-quality samples, wood charcoal is commonly used for radiocarbon dating. Sagebrush (Artemisia tridentata Nutt.), a shrub frequently used for fuel across much of the western United States, seems a potentially better candidate for 14C dating than tree wood since the possibility for significant age discrepancy might be less. A comparison of multiple assays from single features reveals that sagebrush can overestimate age more than even tree wood charcoal. A plausible cause of this appears to be persistence of the shrub on the ground surface for an extended interval after death, such that use as fuel almost invariably occurs hundreds of years after fixation of carbon. The potential for age discrepancy may decrease as population density increases because the demand for fuel wood would have resulted in a more rapid turnover of the fuel biomass. This is not true for Archaic period foragers of western North America when population levels were likely quite low and residential mobility quite high.
    • Radiocarbon Chronology of Central Alaska: Technological Continuity and Economic Change

      Potter, Ben A. (Department of Geosciences, The University of Arizona, 2008-01-01)
      This research presents the first comprehensive radiocarbon chronology for central Alaska, encompassing the late Pleistocene and Holocene archaeological record. Dated component distributions, comprised of 274 14C dates from 160 components, indicate changing land-use strategies and subsistence economies, reflecting primarily lowland exploitation of bison, wapiti, and birds prior to 6000 cal BP, followed by increasing caribou and fish exploitation and use of upland areas. Microblade technology is conserved from the earliest components to ~1000 cal BP, and this continuity is not reflected in current cultural history sequences. Using component abundance as a proxy for population, initial colonization is associated with climate amelioration after ~14,000 cal BP, and population declines are associated with the Younger Dryas (13,000-12,000 cal BP) and initial establishment of widespread spruce forests (10,000-9000 cal BP).
    • 14C Dating of the Upper Paleolithic Site at Krems-Hundssteig in Lower Austria

      Wild, E. M.; Neugebauer-Maresch, C.; Einwögerer, T.; Stadler, P.; Steier, P.; Brock, F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      The open-air archaeological site at Krems-Hundssteig is a well-known Upper Paleolithic site located in Lower Austria. The site was discovered in the late 19th/early 20th centuries when a large number of archaeological remains were collected during the course of loess quarrying. Although no systematic excavation has ever been performed, Krems-Hundssteig has been described since its discovery as typical of the Aurignacian period in this region based on the numerous archaeological finds; accordingly, the culture has been named Kremsien by some authors. Surprisingly, the artifacts found in a recent excavation adjacent to this location showed solely Gravettian features, calling into question the original assignment to the Aurignacian. Although the earlier assignment was supported by a radiocarbon date of ~35 kyr BP (Hahn 1977), new accelerator mass spectrometry (AMS) 14C dates proved that the recently excavated cultural layer originates from the Gravettian period. Older paleosols were also detected by sondage drillings at some depth below it. The new results indicate that a large Aurignacian level and a substantial complex of Gravettian layers are present in this area. Therefore, it must be assumed that more than 1 cultural level was affected and destroyed by the historic loess quarrying, and that the assemblage of Krems-Hundssteig artifacts, traditionally ascribed to the Aurignacian, might be interspersed with Gravettian pieces.
    • Bayesian Refinement of a Stratified Sequence of Radiometric Dates from Punta de Chimino, Guatemala

      Bachand, Bruce R. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Bayesian analysis of 6 radiocarbon and 2 luminescence determinations from Punta de Chiminos acropolis provides subcentury chronometric accuracy for a Protoclassic hiatus and a more decisive, incipient Early Classic abandonment. For the latter event, sensitivity tests and a redundant modal value pattern reduce the period of historical interest from a few centuries to several decades. The findings aid in selecting between 2 historical scenarios and demonstrate that improved chronological accuracy is attainable for sites and contexts lacking calendrical dates.
    • A New Chronology for Pololu Valley, Hawai'i Island: Occupational History and Agricultural Development

      Julie S. Field; Graves, Michael W. (Department of Geosciences, The University of Arizona, 2008-01-01)
      A reanalysis of the chronology of Pololu Valley, located in the district of Kohala on Hawai'i Island, is presented using standard radiocarbon and accelerator mass spectrometry (AMS) dating. Using curated materials from the 1970s, Pololu is reassessed and found to have the earliest coastal occupations in this part of Hawai'i, beginning about AD 1300. Occupations at the dunes and in the valley interior are investigated, as are dryland and wetland field agricultural systems. These data provide a refined model for expansion and intensification of agricultural production in the 15th-17th centuries, and link this remote valley to demographic and sociopolitical trends that were occurring in the rest of Hawai'i.
    • Development of Sample Pretreatment of Silk for Radiocarbon Dating

      Kim, Kyeong Ja; Southon, John; Imamura, Mineo; Sparks, Rodger (Department of Geosciences, The University of Arizona, 2008-01-01)
      We have developed sample pretreatments for silk for radiocarbon dating. Characteristics of silk under different types of pretreatment were investigated, as well as the behavior of dye and possible contaminants. We found that dye could be removed completely, together with all other foreign materials bigger than 1.2 m, using a glass microfiber filter after decomposition with 6N HCl. The decomposed proteins were concentrated using Centriprep ultrafiltration concentrators with 3 different molecular weight cut-offs. By taking a molecular weight fractionwhich selects for secondary structures of silk protein14C dating of silk samples can be made more reliable. This study confirms that uniformly fractured polypeptide chains of silk provide an appropriate fraction for 14C age dating to select silk protein against dye particles and undecomposed foreign contaminants.
    • AMS Radiocarbon Dating of Giant Rock Scallop (Hinnites Multirugosus) Artifacts from San Miguel Island, California, USA

      Braje, Todd J.; Rick, Torben C.; Erlandson, Jon M. (Department of Geosciences, The University of Arizona, 2008-01-01)
      For at least 100,000 yr, marine shell beads have been important ornamental and symbolic artifacts intimately associated with the behavior of anatomically modern humans. In California, giant rock scallop (Hinnites multirugosus) beads were once thought to have been used only for the last 1000 yr, where they were considered to be markers of high social status among the Chumash Indians of the Santa Barbara Channel region. Direct accelerator mass spectrometry (AMS) radiocarbon dating of 1 giant rock scallop ornament and 2 beads from San Miguel Island extends the use of this shell for personal adornment to at least 8000 cal BP. Our study emphasizes the importance of direct AMS 14C dating of artifacts to enhance cultural chronologies and clarify the antiquity of various technologies and associated behaviors. Our results also caution archaeologists when equating artifact rarity with sociopolitical complexity.
    • Towards a Deeper Understanding of How Carbonate Isotopes (14C, 13C, 18O) Reflect Environmental Changes: A Study with Recent 210Pb-Dated Sediments of the Plitvice Lakes, Croatia

      Horvatinčić, Nada; Barešić, Jadranka; Babinka, Slavica; Obelić, Bogomil; Krajcar Bronić, Ines; Vreča, Polona; Sucrow, Axel (Department of Geosciences, The University of Arizona, 2008-01-01)
      Five short cores (top 40-45 cm of sediment) from 4 lakes of the Plitvice Lakes system (Croatia) were measured for 210Pb, 137Cs, a14C, 13C, and 18O in order to study the influence of environmental changes on the sediment system in small and large lakes. Sediment chronology based on the constant flux (CF) 210Pb model was the most reliable. Lake sediments consisted mainly of autochthonous carbonates with higher sedimentation rates in small lakes. Sediments from 2 large lakes, Proće and Kozjak, showed constant stable isotope profiles for the carbonate fraction and full agreement between the 137Cs and 210Pb chronologies. Sediments from 2 small lakes, Gradinsko and Kaluderovac, showed synchronous increases in 14C and 13C and disturbed 137Cs records. All lakes showed an increase in a14C in the carbonate sediments above the first occurrence of 137Cs, which was interpreted as a damped (~10 pMC increase in a14C) and decades-delayed consequence of the bomb-induced increase in a14C in atmospheric CO2. For the small lakes, increased 13C in the last 2 decades and part of the a14C increase is probably due to an increase in primary productivity, which enhanced biologically induced calcite precipitation with concomitant changes in the carbon isotopic composition of carbonate sediments. 13C values of a near-shore sediment core close to the confluence of one of the tributaries of Lake Kozjak showed that the carbonates in this core are a mixture of autochthonous and eroded allochthonous mineral carbonate. This core had a higher fraction of organic material. The sedimentation rate at this core site was high, but rates could not be quantified by 210Pb, 137Cs, or 14C.
    • AMS Dating on the Shell Bar Section from Qaidam Basin, NE Tibetan Plateau, China

      Zhang, H. C.; Fan, H. F.; Chang, F. Q.; Zhang, W. X.; Lei, G. L.; Yang, M. S.; Lei, Y. B.; Yang, L. Q. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Radiocarbon dating by accelerator mass spectrometry (AMS) of the shell bar section of Qaidam Basin, NE Tibetan Plateau, shows that this section was formed between ~39.7 and ~17.5 14C kyr BP and represented the highest paleolake development period since the Late Pleistocene. It was difficult to obtain reliable dates due to the low organic carbon content, which was formed mainly by authochtonous algae-bacteria (Zhang et al. 2007a). In order to improve the dating, 14C ages of both the alkali residual and acid-soluble components of the organic carbon were measured to check the consistency of the dating results. Total organic carbon (TOC) content and stable carbon isotopes (delta-13Corg) might also be used as critical references for checking the reliability of dates. For example, in our study of the shell bar section from Qaidam Basin, we found that when the TOC content was higher than 0.15% and/or delta-13Corg was lower than -23‰, the AMS dates were reliable. AMS dating of fossil shells demonstrated that they could provide valuable age information. The ages given by fossil shells are comparable to those of bulk carbonate from a similar sampling site, and are about 15~18 kyr older than the ages given by organic matter. Due to the U/Th dating requirements and open nature of the system, we concluded that U/Th dating results are unreliable and that this technique is unsuitable for dating halite deposits from Qaidam Basin.
    • Estimated Reservoir Ages of the Black Sea since the Last Glacial

      Kwiecien, O.; Arz, H. W.; Lamy, F.; Wulf, S.; Bahr, A.; Röhl, U.; Haug, G. H. (Department of Geosciences, The University of Arizona, 2008-01-01)
      Accelerator mass spectrometry (AMS) radiocarbon dating of ostracod and gastropod shells from the southwestern Black Sea cores combined with tephrochronology provides the basis for studying reservoir age changes in the late-glacial Black Sea. The comparison of our data with records from the northwestern Black Sea shows that an apparent reservoir age of ~1450 14C yr found in the glacial is characteristic of a homogenized water column. This apparent reservoir age is most likely due to the hardwater effect. Though data indicate that a reservoir age of ~1450 14C yr may have persisted until the Blling-Allerd warm period, a comparison with the GISP2 ice-core record suggests a gradual reduction of the reservoir age to ~1000 14C yr, which might have been caused by dilution effects of inflowing meltwater. During the Blling-Allerd warm period, soil development and increased vegetation cover in the catchment area of the Black Sea could have hampered erosion of carbonate bedrock, and hence diminished contamination by old carbon brought to the Black Sea basin by rivers. A further reduction of the reservoir age most probably occurred contemporary to the precipitation of inorganic carbonates triggered by increased phytoplankton activity, and was confined to the upper water column. Intensified deep water formation subsequently enhanced the mixing/convection and renewal of intermediate water. During the Younger Dryas, the age of the upper water column was close to 0 yr, while the intermediate water was ~900 14C yr older. The first inflow of saline Mediterranean water, at ~8300 14C yr BP, shifted the surface water age towards the recent value of ~400 14C yr.
    • Obituary: Grant Kocharov

      Dergachev, Valentin; Ostrykov, Valery; Gladysheva, Olga; Koudriavtsev, Igor; Ogurtsov, Maxim; Dreschoff, Gisela; Jungner, Högne (Department of Geosciences, The University of Arizona, 2008-01-01)
    • Editorial Board

      Department of Geosciences, The University of Arizona, 2008-01-01
    • New 14C Ages on Cellulose from Diprotodon Gut Contents: Explorations in Oxidation Chemistry and Combustion

      Gillespie, Richard; Fifield, L. Keith; Levchenko, Vladimir; Wells, Rod (Department of Geosciences, The University of Arizona, 2008-01-01)
      We report radiocarbon ages on cellulose isolated from the gut contents of a Diprotodon found at Lake Callabonna, South Australia. The maximum age obtained corresponds to a minimum age of 53,400 BP for this extinct giant marsupial. This is older than, and hence consistent with, the generally accepted Australian megafauna extinction window. We argue that dichromate and other strong oxidants are less selective than chlorite for lignin destruction in wood, and our results suggest that ages approaching laboratory background can be obtained using a repeated pretreatment sequence of chlorite-alkali-acid and measurement of the sometimes discarded 330 C combustion fraction.
    • New Marine ΔR Values for the South Pacific Subtropical Gyre Region

      Petchey, Fiona; Anderson, Atholl; Zondervan, Albert; Ulm, Sean; Hogg, Alan (Department of Geosciences, The University of Arizona, 2008-01-01)
      This paper presents 31 new R results of known-age, pre-AD 1950 shells from the South Pacific subtropical gyre region, spanning from the Tuamotu Archipelago in the east to New Caledonia in the west. This doubles the number of available R values for the Oceania region. These values indicate that the regional offset (R) from the modeled radiocarbon marine age has remained relatively constant over the last 100 yr prior to 1950. Variation from the norm can be attributed to various influences including localized upwelling around islands, the presence of a hardwater effect, direct ingestion of old carbon by the live shellfish, or enhanced exchange with atmospheric CO2 as a consequence of photosynthetic activity or increased aeration.
    • New Radiocarbon Dates for the Baden Culture

      Horvath, Tunde; Svingor, S. Éva; Molnár, Mihaly (Department of Geosciences, The University of Arizona, 2008-01-01)
      In 2001-2002, a settlement of the Baden culture was excavated in the vicinity of Balatonőszd. During the rescue excavation along the M7 highway, in an area of 100,000 m2, 2800 pits dug into the subsoil, 320 hearths, and cultural layers rich in material were discovered. The material of the Baden culture represents phases IB-IC (Boleraz), IIA (Transitional), IIB-III (Early Classical) according to Němejcov-Pavkov's (1981, 1998) typological system. We took 20 samples from the large number of human and animal skeletons for radiocarbon dating, of which 16 measurements were successful. These results provide absolute dates for a Baden culture settlement with the longest occupation and the largest excavated surface in Hungary. This provides an opportunity to review the chronological position of the Baden culture, with special emphasis on its beginning and end.
    • Zinc Reduction as an Alternative Method for AMS Radiocarbon Dating: Process Optimization at CIRCE

      Marzaioli, F.; Borriello, G.; Passariello, I.; Lubritto, C.; De Cesare, N.; D'Onofrio, A.; Terrasi, F. (Department of Geosciences, The University of Arizona, 2008-01-01)
      The pretreatment of samples for radiocarbon measurements, transforming a variety of materials into graphite solid targets, represents a critical point in the accelerator mass spectrometry (AMS) procedure. We describe the new, state-of-the-art CIRCE AMS preparation laboratory, particularly the setup and optimization of an alternative method, the zinc reduction method, for graphite target production, compared to the more common hydrogen reduction method. Measured 14C values on standard and blank samples reduced via zinc reaction revealed mean background levels, accuracy, and sensitivity comparable to those obtained by our conventional hydrogen reaction lines. Zinc line reduction at the CIRCE laboratory represents an effective and powerful alternative to the conventional hydrogen reduction, ensuring higher sample throughput with lower costs at a comparable performance level.
    • Very Long-Lived Mollusks Confirm 17th Century AD Tephra-Based Radiocarbon Reservoir Ages for North Icelandic Shelf Waters

      Wanamaker, Alan D., Jr.; Heinemeier, Jan; Scourse, James D.; Richardson, Christopher A.; Butler, Paul G.; Eiríksson, Jon; Knudsen, Karen Luise (Department of Geosciences, The University of Arizona, 2008-01-01)
      Marine sediment records from the north Icelandic shelf, which rely on tephrochronological age models, reveal an average Delta-R (regional deviation from the modeled global surface ocean reservoir age) of approximately 150 yr for the last millennium. These tephra-based age models have not hitherto been independently verified. Here, we provide data that corroborate Delta-R values derived from these sediment archives. We sampled the youngest portion (ontogenetic age) of a bivalve shell, Arctica islandica (L.), for radiocarbon analysis, which was collected alive in 2006 from the north Icelandic shelf in ~80 m water depth. Annual band counting from the sectioned shell revealed that this clam lived for more than 405 yr, making it the longest-lived mollusk and possibly the oldest non-colonial animal yet documented. The 14C age derived from the umbo region of the shell is 951 +/- 27 yr BP. Assuming that the bivalve settled onto the seabed at AD 1600, the corresponding local value of Delta-R is found to be 237 +/- 35 yr by comparison of the 14C age with the Marine04 calibration curve (Hughen et al. 2004) at this time. Furthermore, we cross-matched a 287-yr-old, dead-collected, A. islandica shell from AD 1601 to 1656 from the same site with the live-caught individual. 14C analysis from the ventral margin of this shell revealed a Delta-R of 186 +/- 50 yr at AD 1650. These values compare favorably with each other and with the tephra-based Delta-R values during this period, illustrating that 14C from A. islandica can effectively record 14C reservoir changes in the shelf seas.