• Protocol Development for Purification and Characterization of Sub-Fossil Insect Chitin for Stable Isotopic Analysis and Radiocarbon Dating

      Hodgins, Gregory W. L.; Thorpe, J. L.; Coope, G. R.; Hedges, Robert E. M. (Department of Geosciences, The University of Arizona, 2001-01-01)
      Reliable radiocarbon dating depends upon well-defined samples. We have been investigating whether or not reliable 14C dates can be obtained directly from sub-fossil insect cuticle or biochemical fractions derived from it. Initial carbon and nitrogen stable isotope measurements on sub-fossil insect chitin from species with known feeding behaviors found within a single site (St Bees, Cumbria) clustered in a manner reminiscent of trophic level effects seen in terrestrial ecosystems. Although this finding implied some chemical stability, the measurement of CN ratios from the same samples indicated compositional variability. In addition, 14C dates obtained from these same samples were different from dates obtained from plant macrofossils found at the same depth. We have experimented with protocols designed to biochemically reduce chitin to its principle carbohydrate component glucosamine with the aim of using this compound to generate reliable 14C dates. Solvent extractions of sub-fossil chitin were carried out to remove both endogenous and exogenous lipid-soluble materials. Base hydrolysis reactions designed to extract polypeptides retained surprisingly high levels of contaminating amino acids. Proteinase K enzyme treatment had little affect on the level of amino acid contamination. Strong acid hydrolysis reactions designed to depolymerize chitin to glucosamine yielded only 5% glucosamine. Clearly alternative methods of chitin depolymerization must be identified before the purification and 14C dating of glucosamine from sub-fossil chitin becomes practical.
    • Sample Preparation of Dissolved Organic Carbon in Groundwater for AMS 14C Analysis

      Burr, George S.; Thomas, J. M.; Reines, D.; Jeffrey, D.; Courtney, C.; Jull, A. J. Timothy; Lange, Todd (Department of Geosciences, The University of Arizona, 2001-01-01)
      This study describes a sample preparation technique used to isolate dissolved organic carbon (DOC) in groundwater for radiocarbon analysis using accelerator mass spectrometry (AMS). The goal of the work is to improve our ability to determine groundwater residence times based on 14C measurements of the DOC fraction in groundwater. Water samples were collected from carbonate and volcanic rock aquifers in southern Nevada. Multiple measurements of total dissolved organic carbon (TDOC) in groundwater from one site are used to demonstrate the reproducibility of the analytical procedure. The reproducibility of the method is about one percent (1sigma) for a 0.5 mg sample. The procedural blank for the same size sample contains about 1 percent modern carbon (pMC).
    • Seasonal Fluctuation of Stable Carbon Isotopic Composition in Japanese Cypress Tree Rings from the Last Glacial Period—Possibility of Paleoenvironment Reconstruction

      Takahashi, Hiroshi Aoki; Yonenobu, Hitoshi; Nakamura, Toshio; Wada, Hideki (Department of Geosciences, The University of Arizona, 2001-01-01)
      Seasonal variations of delta-13C were analyzed for two Japanese cypress trees (Chamaecyparis obtusa), one buried and one living. Both trees were different in age but sampled in areas geographically close to each other in central Japan. A buried cypress with 394 annual rings was excavated from Old Fuji mudflow, the last glacial strata of the dormant Mt. Fuji volcano. The accelerator mass spectrometry (AMS) radiocarbon date of this glacial sample was 18,600 +/120 BP (NUTA-4884). A living tree stem, which has 192 rings, was cut from the Izu Peninsula in 1986. In order to measure the seasonal delta-13C fluctuation, the tree rings were divided equally into three earlywood and one or two latewood consecutive sections. The delta-13C value within an annual ring generally increased from the first to the third or fourth sections then decreased in the last section. This pattern of the variation was similar in the glacial and modern samples. The delta-13C value within an annual ring seems to be controlled by environmental factors (not plant physiological ones), since there was no isotopic shift in the seasonal delta-13C variation at the earlywood-latewood boundary, which was controlled by plant physiology. The result suggests the potential to reconstruct the paleoenvironment within a year using the seasonal delta-13C variation, though site-specific conditions such as soil characteristics would also affect to its fluctuation.