• 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.
    • Water Column Profiles of Dissolved Inorganic Radiocarbon for the Kuroshio Region, Offshore of the Southern Japanese Coast

      Tsuboi, Tatsuya; Iwata, Hiroshi; Wada, Hideki; Matsuzaki, Hiroyuki; Sohrin, Rumi; Hiroe, Yutaka; Ichikawa, Tadafumi; Hidaka, Kiyotaka; Watanabe, Tomoo (Department of Geosciences, The University of Arizona, 2011-12-16)
      We present the water column profiles (surface to 2000 m depth) for dissolved inorganic radiocarbon ([delta]14CDIC) from 2 stations in the Kuroshio region including the Kuroshio large meander (LM) of 2004–2005. Surprisingly, the [delta]14CDIC value varied up to 125‰ in the intermediate layer, especially near 600 m depth. In addition, the [delta]14CDIC value was approximately -150‰ at 200 m depth at the northern station of Kuroshio in August 2005. This value is ~100‰ less than other [delta]14CDIC values for the same depth. In comparison, the [delta]14CDIC water column profiles for the southern station of Kuroshio and GEOSECS station 224 decrease down to 600 m depth and were similar below 600 m depth. Our results suggest that strong upwelling associated with the Kuroshio LM has a powerful influence on the [delta]14CDIC water column profiles in the study region.