• Radiocarbon Measurements of Tree Rings from 14 ka Huon Pine

      Lange, Todd; Barbetti, M.; Donahue, Douglas J. (Department of Geosciences, The University of Arizona, 2001-01-01)
      We have measured the radiocarbon content of tree rings from a section of Huon pine retrieved from Tasmania. The sample was divided into 39 five-ring sub-samples covering a period of 194 years. Radiocarbon ages of each of these sub-samples was determined by making four measurements of each sub-sample at the Arizona AMS laboratory (Table 1). The resulting 1-sigma precisions are about 0.5%. A comparison of our data with the appropriate curve in INTCAL98 indicates that the calendar age of our sample is close to 14,000 cal BP. Using this age calibration, we have constructed a plot of Delta-14C versus assumed calendar age. This plot shows an essentially constant value over the youngest 125 rings of our sample. Over the oldest 75 yr of the sample, the Delta-14C curve exhibits three fluctuations, the largest of which is about 65 per mil. The time of the peaks in the Huon-pine 14C curve corresponds approximately with the European Bolling/Allerod climatic event. Work is in progress to extend the data 100 yr more toward older ages.
    • 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.