• Diet-Derived Variations in Radiocarbon and Stable Isotopes: A Case Study from Shag River Mouth, New Zealand

      Higham, Thomas; Anderson, Atholl; Bronk Ramsey, Christopher; Tompkins, Christine (Department of Geosciences, The University of Arizona, 2005-01-01)
      Accelerator mass spectrometry (AMS) determinations of rat bones from natural and cultural sites in New Zealand have produced ages at odds with the accepted date for early human settlement by over 1000 yr. Since rats are a human commensal, this implies either an earlier visitation by people or problems with the reliability of the AMS determinations. One explanation for the extreme ages is dietary variation involving movement of depleted radiocarbon through dietary food chains to rats. To investigate this, we 14C dated fauna from the previously well-dated site of Shag River Mouth. The faunal remains were of species that consumed carbon derived from a variety of environments within the orbit of the site, including the estuary, river, land, and sea. The 14C results showed a wide range in age among estuarine and freshwater species. Terrestrial and marine organisms produced ages within expectations. We also found differences between bone dated using the Oxford ultrafiltration method and those treated using the filtered gelatin method. This implies that contamination could also be of greater importance than previously thought.
    • Influence of Mollusk Species on Marine ΔR Determinations

      Ascough, Philippa L.; Cook, Gordon T.; Dugmore, Andrew J.; Scott, E. Marian; Freeman, Stewart T. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Radiocarbon ages were measured on replicate samples of burnt grain and 5 mollusk species collected from a single sealed layer at an archaeological site (Hornish Point) on the west coast of South Uist, Scotland. The aim was to examine the impact of using different mollusk species on Delta-R determinations that are calculated using the paired terrestrial/marine sample approach. The mollusk species examined inhabit a range of environments and utilize a variety of food sources within the intertidal zone. Several authors have suggested that these factors may be responsible for observed variations in the 14C activity of mollusk shells that were contemporaneous in a single location. This study found no significant variation in the 14C ages of the mollusk species, and consequently, no significant variation in calculated values of Delta-R. The implication is that in an area where there are no carboniferous rocks or significant local inputs of freshwater to the surface ocean, any of a range of marine mollusk species can be used in combination with short-lived terrestrial material from the same secure archaeological context to accurately determine a R value for a particular geographic location and period in time.
    • Progress in AMS Target Production of Sub-Milligram Samples at the NERC Radiocarbon Laboratory

      Ertunç, Tanya; Xu, Sheng; Bryant, Charlotte L.; Maden, Colin; Murray, Callum; Currie, Margaret; Freeman, Stewart P. H. T. (Department of Geosciences, The University of Arizona, 2005-01-01)
      Recent progress in graphite target production for sub-milligram environmental samples in our facility is presented. We describe an optimized hydrolysis procedure now routinely used for the preparation of CO2 from inorganic samples, a new high-vacuum line dedicated to small sample processing (combining sample distillation and graphitization units), as well as a modified graphitization procedure. Although measurements of graphite targets as small as 35 micrograms C have been achieved, system background and measurement uncertainties increase significantly below 150 micrograms C. As target lifetime can become critically short for targets <150 micrograms C, the facility currently only processes inorganic samples down to 150 micrograms C. All radiocarbon measurements are made at the Scottish Universities Environmental Research Centre (SUERC) accelerator mass spectrometry (AMS) facility. Sample processing and analysis are labor-intensive, taking approximately 3 times longer than samples greater than or equal to 500 micrograms C. The technical details of the new system, graphitization yield, fractionation introduced during the process, and the system blank are discussed in detail.
    • Radiocarbon Dates from the Catacombs of St. Callixtus in Rome

      Rutgers, Leonard V.; van der Borg, Klaas; de Jong, Arie F. M. (Department of Geosciences, The University of Arizona, 2005-01-01)
      This paper reports the first chronological assessment of the Christian catacombs of Rome by radiocarbon dating. The organic materials dated were found in a set of burial rooms in the so-called Liberian region of the catacombs of St. Callixtus on the Appian Way. 14C dating of small samples by accelerator mass spectrometry (AMS) represents a major advance over traditional archaeological dating methods used in catacomb archaeology; however, AMS 14C dating raises questions about sample reliability and chronological evaluation. We briefly explore these questions.
    • Radiocarbon Dating of Alkenones from Marine Sediments: I. Isolation Protocol

      Ohkouchi, Naohiko; Xu, Li; Reddy, Christopher M.; Montluçon, Daniel; Linton, Timothy I. (Department of Geosciences, The University of Arizona, 2005-01-01)
      The chemical and isotopic compositions of long-chain (C3 6-C3 9) unsaturated ketones (alkenones), a unique class of algal lipids, encode surface ocean properties useful for paleoceanographic reconstruction. Recently, we have sought to extend the utility of alkenones as oceanic tracers through measurement of their radiocarbon contents. Here, we describe a method for isolation of alkenones from sediments as a compound class based on a sequence of wet chemical techniques. The steps involved, which include silica gel column chromatography, urea adduction, and silver nitrate-silica gel column chromatography, exploit various structural attributes of the alkenones. Amounts of purified alkenones estimated by GC/FID measurements were highly correlated with CO2 yields after sample combustion, indicating purities of greater than 90% for samples containing greater than or equal to 100 micrograms C. The degree of alkenone unsaturation (U^(K')37) also varied minimally through the procedure. We also describe a high-performance liquid chromatography (HPLC) method to isolate individual alkenones for molecular-level structural and isotopic determination.
    • Radiocarbon Dating of Alkenones from Marine Sediments: II. Assessment of Carbon Process Blanks

      Mollenhauer, Gesine; Montlucon, Daniel; Eglinton, Timothy I. (Department of Geosciences, The University of Arizona, 2005-01-01)
      We evaluate potential process blanks associated with radiocarbon measurement of microgram to milligram quantities of alkenones at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility. Two strategies to constrain the contribution of blanks to alkenone 14C dates were followed: 1) dating of samples of known age and 2) multiple measurements of identical samples. We show that the potential contamination associated with the procedure does not lead to a systematic bias of the results of alkenone dating to either younger or older ages. Our results indicate that alkenones record ∆14C of ambient DIC with an accuracy of approximately 10. A conservative estimate of measurement precision is 17ppm for modern samples. Alkenone 14C ages are expected to be reliable within 500 yr for samples younger than 10,500 14C yr.
    • Radiocarbon Dating of Alkenones from Marine Sediments: III. Influence of Solvent Extraction Procedures on 14C Measurements of Foraminifera

      Ohkouchi, Naohiko; Eglinton, Timothy I.; Hughen, Konrad A.; Roosen, Ellen; Keigwin, Lloyd D. (Department of Geosciences, The University of Arizona, 2005-01-01)
      As a result of the growing use of multiple geochemical proxies to reconstruct ocean and climate changes in the past, there is an increasing need to establish temporal relationships between proxies derived from the same marine sediment record and ideally from the same core sections. Coupled proxy records of surface ocean properties, such as those based on lipid biomarkers (e.g. Alkenone-derived sea surface temperature) and planktonic foraminiferal carbonate (oxygen isotopes), are a key example. Here, we assess whether 2 different solvent extraction procedures used for isolation of molecular biomarkers influence the radiocarbon contents of planktonic foraminiferal carbonate recovered from the corresponding residues of Bermuda Rise and Cariaco Basin sediments. Although minor ∆14C differences were observed between solvent-extracted and unextracted samples, no substantial or systematic offsets were evident. Overall, these data suggest that, in a practical sense, foraminiferal shells from a solvent-extracted residue can be reliably used for 14C dating to determine the age of sediment deposition and to examine age relationships with other sedimentary constituents (e.g. Alkenones).
    • Radiocarbon Laboratories

      Department of Geosciences, The University of Arizona, 2005-01-01
      This is Radiocarbons annual list of active radiocarbon laboratories and personnel known to us. Conventional beta-counting facilities are listed in Part I, and accelerator mass spectrometry (AMS) facilities in Part II. Laboratory code designations, used to identify published dates, are given to the left of the listing.
    • Radiocarbon Updates

      Department of Geosciences, The University of Arizona, 2005-01-01
      New Laboratories, Upcoming Conferences
    • Radiocarbon, Soil, and Artifact Chronologies for an Early Southern Oregon Coastal Site

      Hall, Roberta; Davis, Loren G.; Willis, Samuel; Fillmore, Matthew (Department of Geosciences, The University of Arizona, 2005-01-01)
      Radiocarbon dates together with geoarchaeological, soil, and lithic analyses are presented to describe archaeological site 35-CS-9 in Bandon Ocean Wayside State Park, Oregon, northwestern USA. One of the few Oregon middleHolocene coastal sites that includes sediments and artifacts dating to the early Holocene and possibly to the late Pleistocene, it was recorded in 1951 and surface surveyed by archaeologists in 1975, 1986, and 1991, but its depth and antiquity were not tested. In February 2002, we studied the sites stratigraphy and sediments and described 8 strata from the aeolian surface to bedrock at 350 cm depth. Soil samples taken from a cut bank for texture classification, particle size analysis, pH, carbon content, and chemical analysis suggested that the site represented a complete history of Holocene deposits. Excavation of 2 test units in August 2002 uncovered substantial lithic and charcoal remains that confirm a protracted middle-Holocene occupation and suggest that human occupation began in the early Holocene. Charcoal recovered at 235-245 cm dated to 11,000 14C BP, and the deepest lithic artifact was recovered in a level at 215-225 cm. Whether the human occupation was continuous throughout the Holocene, and whether it began in the early Holocene or in the late Pleistocene, can only be determined with further excavations.
    • Re-Dating Mid-Holocene Betelnut (Areca Catechu L.) and Other Plant Use at Dongan, Papua New Guinea

      Fairbairn, Andrew; Swadling, Pamela (Department of Geosciences, The University of Arizona, 2005-01-01)
      Direct accelerator mass spectrometry (AMS) dating of anaerobically preserved plant remains from the Dongan site in New Guinea, combined with assessment of preservation condition, confirms earlier doubts about the antiquity of betelnut (Areca catechu L.) found at the site. A possible sago leaf fragment is also identified as a modern contaminant. The midHolocene age of other fruit and nut remains is verified using these methods. The utility of AMS dating in combination with detailed archaeobotanical assessment is demonstrated, thus improving chronometric hygiene and with it knowledge of past plant use in Oceania.
    • Testing the “Dicarb Problem”: A Case Study from North Alaska

      Reuther, Joshua D.; Gerlach, S. Craig (Department of Geosciences, The University of Arizona, 2005-01-01)
      An assumption exists in North Alaskan archaeological literature that radiometric assays produced by the nowdefunct Dicarb Radioisotope Co. (Dicarb) are too young or more recent when compared to those produced by other laboratories. This assumption is statistically tested by comparing radiocarbon assays produced by Dicarb to those produced by Beta Analytic, Inc.; Geochron Laboratories; and the NSF-Arizona AMS Facility. The primary data set consists of radiometric and accelerator mass spectrometry (AMS) assays produced from materials excavated at the Croxton site, Locality J, Tukuto Lake, northern Alaska. Statistical analyses demonstrate that 14C assays produced by Dicarb tend to be "younger" than assays produced by other laboratories on crosscheck samples, with differences ranging between 350 and 1440 yr.