• A Direct Method to Measure 14CO2 Lost by Evasion from Surface Waters

      Billett, M. F.; Garnett, M. H.; Hardie, S. L. (Department of Geosciences, The University of Arizona, 2006-01-01)
      Recent methodological advances in the use of zeolite molecular sieves for measuring the isotopic signature of CO2 have provided the opportunity to make direct measurements of 14CO2 in various field situations. We linked a portable molecular sieve/pump/IRGA system to a floating chamber to demonstrate the potential of the method to quantify the isotopic signature (d13C and 14C) of CO2 lost by evasion (outgassing) from surface waters. The system, which was tested on a peatland stream in Scotland, involved 1) an initial period of scrubbing ambient CO2 from the chamber, 2) a period of CO2 build-up caused by surface water evasion, and 3) a final period of CO2 collection by the molecular sieve cartridge. The field test at 2 different sites on the same drainage system suggested that the results were reproducible in terms of d13C and 14C values. These represent the first direct measurements of the isotopic signature of CO2 lost by evasion from water surfaces.
    • Book Review: Archaeology in Practice: A Student Guide to Archaeological Analyses, Jane Balme, Alistair Paterson (Eds.)

      Schiffer, M. B. (Department of Geosciences, The University of Arizona, 2006-01-01)
    • Coastal Upwelling and Radiocarbon—Evidence for Temporal Fluctuations in Ocean Reservoir Effect off Portugal During the Holocene

      Monge Soares, António; Alveirinho Dias, João M. (Department of Geosciences, The University of Arizona, 2006-01-01)
      This paper focuses on the use of the radiocarbon content of marine shells collected along the Portuguese coast as a proxy for the intensity of coastal upwelling off of Portugal. Differences in the 14C ages of closely associated marine mollusk shells and terrestrial material (charcoal or bones) from several Portuguese archaeological contexts seem to be significant throughout the Holocene. Delta-R values range from 940 +/50 to 160 +/40 14C yr. Five of these values are significantly higher than the modern value (250 +/25 14C yr), while the remaining values are lower. The modern value was calculated by measuring the 14C content of live-collected, pre-bomb marine mollusk shells. This value is in accordance with an active upwelling of strong intensity that currently occurs off of Portugal. Some primary observations based on data presented here can be made: i) during the Holocene important changes have occurred in the ocean reservoir effect off the Portuguese coast; ii) these fluctuations may be correlated with regional oceanographic changes, namely with changes in the strength of coastal upwelling; and iii) these changes suggest some sort of variability of the climatic factors forcing coastal upwelling off of Portugal.
    • Comment On “Diet-Derived Variations in Radiocarbon and Stable Isotopes: A Case Study from Shag River Mouth, New Zealand”

      Beavan Athfield, Nancy (Department of Geosciences, The University of Arizona, 2006-01-01)
    • Dating Paleosol and Animal Remains in Loess Deposits

      Zhang, H. C.; Li, B.; Yang, M. S.; Lei, G. L.; Ding, H.; Niu, Jie; Fan, H. F.; Zhang, W. X.; Chang, F. Q. (Department of Geosciences, The University of Arizona, 2006-01-01)
      Accurate and reliable dating of paleosols, animal remains, and artifacts is of crucial importance in reconstructing environmental change and understanding the interrelationship between human activities and natural environments. Dating different materials in the same sample can help resolve problems such as soil carbon sources and carbon storage state. Conventional radiocarbon dating of soil (inorganic and organic matter) and accelerator mass spectrometry (AMS) dating of animal remains (fossil bones and teeth) result in different ages for materials from the same sample position in a typical loess section at Xinglong Mountain, Yuzhong County, Gansu Province in NW China. Inorganic matter is ~3400 yr older than organic matter, 4175 +/175 cal BP to 3808 +/90 cal BP. A 1610-yr difference between the 14C ages of fossils (animal bones and teeth) and soil organic matter suggests that a depositional hiatus exists in the studied profile. The varying 14C ages of fossils and soil organic and inorganic matter have important implications for paleoclimate reconstructions from loess sections. It is critical to consider the meaning of the variable 14C ages from different material components from the same sample position in terms of soil organic and inorganic carbon storage, vegetation history reconstruction, archaeology, and the study of ancient civilizations.
    • ENEA Radiocarbon Measurements I

      Magnani, Giuseppe; Bartolomei, Paolo; L, Teresa; Marino, Ernesto Claudio; Govoni, Claudio (Department of Geosciences, The University of Arizona, 2006-01-01)
      This paper includes determinations of archeological and geological samples from different sites in central Italy performed at the Ente per le Nuove Tecnologie l'Energia e l'Ambiente (ENEA) Radiocarbon Laboratory. This laboratory has been in operation since 1985 at the ENEA Bologna Research Center.
    • Letter to the Editor

      Harbottle, Garman (Department of Geosciences, The University of Arizona, 2006-01-01)
    • Marine Radiocarbon Reservoir Ages in Scottish Coastal and Fjordic Waters

      Cage, Alix G.; Heinemeier, Jan; Austin, William E. N. (Department of Geosciences, The University of Arizona, 2006-01-01)
      High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R[t]) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were 14C dated to provide a means of determining R(t) and hence the regional deviation (R) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with 14C dates from the Scottish west coast (Harkness 1983), yield a regional Delta-R value of 26 +/14 yr. The R of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level >95%) from the Delta-R value of 17 +/14 yr reported for UK coastal waters (Reimer 2005; data after Harkness 1983) and are in good agreement with the coastal Delta-R value of 33 +/93 yr reported by Reimer et al. (2002). Therefore, it is recommended that a regional Delta-R correction of 26 +/14 yr should be applied to modern (i.e. Pre-bomb but not prehistoric) marine 14C dates from the NW coast of Scotland.
    • Paleoproductivity Variations in the Equatorial Arabian Sea: Implications for East African and Indian Summer Rainfalls and the El Niño Frequency

      Tiwari, Manish; Ramesh, Rengaswamy; Bhushan, Ravi; Somayajulu, B. L. K.; Jull, A. J. Timothy; Burr, George S. (Department of Geosciences, The University of Arizona, 2006-01-01)
      We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian Ocean Equatorial Westerlies (IEW). The IEW in turn are positively correlated to the Southern Oscillation Index (SOI), which is a measure of El Nio, Southwest monsoon (SWM), and east African rainfall (EAR). The productivity data show that Indian and east African rainfalls declined from 35,000 calendar yr BP up to the last glacial maximum (LGM), with the maximum El Nio frequency during the last glacial period. From ~14,500 to ~2000 calendar yr BP (i.e. Core top), we find strengthening SWM and EAR along with declining El Nio frequency.
    • Radiocarbon Dates from Neolithic and Bronze Age Hunter-Gatherer Cemeteries in the Cis-Baikal Region of Siberia

      Weber, Andrzej W.; Beukens, Roelf P.; Bazaliiskii, Vladimir I.; Goriunova, Olga I.; Savel'ev, Nikolai A. (Department of Geosciences, The University of Arizona, 2006-01-01)
      Extensive radiocarbon dating of human remains from Neolithic and Bronze Age hunter-gatherer cemeteries in the Cis-Baikal region of Siberia has been undertaken as a part of the multidisciplinary examination of this material conducted by the Baikal Archaeology Project (BAP; http:// baikal.arts.ualberta.ca). Due to the large number of analyzed samples, this paper reports the 14C results only in the context of the basic archaeological information about each of the cemeteries. Comprehensive evaluation, analysis, and interpretation of this entire data set will be undertaken in separate publications. In fact, the dates for one such cemetery have already been examined on 2 recent occasions (Weber et al. 2004, 2005).
    • Radiocarbon Determination of Particulate Organic Carbon in Non-Temperated, Alpine Glacier Ice

      Steier, Peter; Shah, Sunita R.; Drosg, Roswitha; Pearson, Ann; Fedi, Mariaelenea; Kutschera, Walter; Schock, Martin; Wagenbach, Dietmar; Wild, Eva Maria (Department of Geosciences, The University of Arizona, 2006-01-01)
      Dating ice samples from glaciers via radiocarbon is a challenge that requires systematic investigations. This work describes an approach for extraction and accelerator mass spectrometry (AMS) 14C analysis of the particulate organic carbon (POC) fraction in glacier ice samples. Measurements were performed at VERA (Vienna Environmental Research Accelerator) on ice samples obtained mainly from the non-temperated ablation zone of the Grenzgletscher (Grenz Glacier) system (Monte Rosa Massif, Swiss Alps). The samples were obtained from 2 sampling sites situated roughly on a common flow line. The sample masses used were between 0.3 and 1.4 kg of ice, yielding between 18 and 307 micrograms of carbon as POC. The carbon contamination introduced during sample processing varied between 5.4 and 33 micrograms C and originated mainly from the quartz filters and the rinsing liquids used in processing. Minimum sample sizes for successful graphitization of CO2 in our laboratory could be reduced to <10 micrograms carbon, with a background in the graphitization process of ~0.5 micrograms of 40-pMC carbon. Evaluation of the whole procedure via 11 Grenzgletscher samples revealed a surprisingly large scatter of pMC values. We obtain a mean calibrated age of 2100 BC to AD 900 (95.4% confidence level), which is not significantly different for the 2 sampling sites. Discussions of these results suggest that single 14C dates of glacial POC are presently of limited significance. Future improvements with respect to analytical precision and sample characterization are proposed in order to fully explore the POC dating potential.
    • Seawater Radiocarbon Evolution in the Gulf of Alaska: 2002 Observations

      Guilderson, Thomas P.; Roark, E. Brendan; Quay, Paul D.; Flood Page, Sarah; Moy, Christopher (Department of Geosciences, The University of Arizona, 2006-01-01)
      Oceanic uptake and transport of bomb radiocarbon as 14CO2 created by atmospheric nuclear weapons testing in the 1950s and 1960s has been a useful diagnostic for determining the carbon transfer between the ocean and atmosphere. In addition, the distribution of 14C in the ocean can be used as a tracer of oceanic circulation. Results obtained on samples collected in the Gulf of Alaska in the summer of 2002 provide a direct comparison with results in the 1970s during GEOSECS and in the early 1990s during WOCE. The open gyre values are 20-40 lower than those documented in 1991 and 1993 (WOCE), although the general trends as a function of latitude are reproduced. Surface values are still significantly higher than pre-bomb levels (~-105 or lower). In the central gyre, we observe ∆14C values that are lower in comparison to GEOSECS (stn 218) and WOCE P16/P17 to a density of ~26.8 sigma-t. This observation is consistent with the overall decrease in surface ∆14C values and reflects the erosion of the bomb-14C transient. We propose that erosion of the bomb-14C transient is accomplished by entrainment of low-14C water via vertical exchange within the Gulf of Alaska and replenishment of surface and subthermocline waters with waters derived from the far northwest Pacific.
    • Southern Palestinian Chronology: Two Radiocarbon Dates for the Early Bronze Age at Tell El-Hesi (Israel)

      Anderson, Roger W. (Department of Geosciences, The University of Arizona, 2006-01-01)
      Several articles reporting radiocarbon dates of Early Bronze Age (EB) material from excavations in the southern Levant have been published over the last 30 yr. The excavations conducted at Tell el-Hesi have produced material from which 2 additional 14C dates have been extracted to date. The 2 samples confirm the EB dating of Field VI material and suggest EB III settlement at Hesi might be earlier than previously reported based on pottery typology.
    • Testing the Limits: Radiocarbon Dating and the End of the Late Bronze Age

      Hagens, Graham (Department of Geosciences, The University of Arizona, 2006-01-01)
      Archaeometry is becoming an increasingly important tool in chronological research related to events in the Ancient Near East during the 2nd millennium BCE. This paper is a review of recently published radiometric results in an attempt to establish the probable dating range for one particular event that occurred during the last quarter of that millennium, the end of the Late Bronze Age. The conclusion is that in spite of significant improvements in methodology in recent years, the quantity and quality of radiocarbon data are still insufficient to define the range of that date to much better than a century. It is concluded that the most likely date of the Late Bronze/Iron Age transition (here defined by the arrival of Mycenaean LH IIIC:1b pottery in the Levant) is somewhere in the 8-decade range between ~1170 to 1100 BCE. A comparative study of archaeological and historical evidence would appear to favor the lower value.