| 研究実績の概要 |
During FY 2022 research has focused on the study of Holocene reef cores from Kodakara-jima, Kagoshima Prefecture. The objectives were to reconstruct the Holocene history of a high-latitude coral reef ecosystem, to examine the effect of latitude on vertical reef accretion rates, and to investigate the response of coral communities to Holocene sea-level rise in the Ryukyu Islands. The results of this research were compiled in a master’s thesis completed in February 2022 in the department of Earth and Planetary Sciences of Nagoya University. A total of 50 m of cores was described in detail at the Kochi Core Center in May and October 2021. Specifically, the visual description of the cores was conducted to obtain information on (1) lithology, (2) the taxonomic composition of fossil coral and algal assemblages, and (3) the relative abundance of vermetid gastropods, Homotrema (encrusting foraminifer), and macro-borings. In addition, the cores were sampled for taxonomic identification of corals and coralline algae, and for radiometric dating of fossil corals using the C14 method. The taxonomic identification of coralline algae was conducted by Professor Iryu Yasufumi (Tohoku University). Radiometric dating was carried out in Prof. Yusuke Yokoyama’s lab (The University of Tokyo). The results of this study were presented at the 24th annual conference of the Japanese Coral Reef Society in November 2021. Results of previous work on modern and fossil coral communities in the Ryukyu Islands were also presented at the 14th International Coral Reef Symposium in July 2021.
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| 今後の研究の推進方策 |
The remaining budget will be used to advance the study of reef cores stored at the Kochi Core Center (KCC). There are several cores of Quaternary reef material stored at KCC that could be targetted. In particular, the older Pleistocene (>30 ka) sections of IODP 325 cores are being re-visited and the necessity to re-examine specific core sections will be evaluated at the beginning of FY2022. In addition, other cores that will represent prime research targets are six long boreholes (24-120 m in length) drilled into uplifted Pleistocene terraces, three at Okinawa-jima in the Central Ryukyus and three at Yonaguni-jima in
the South Ryukyus, all of them also stored at the Kochi Core Center. Besides the study of reef cores, the budget will also be used to study Quaternary reef growth history in Okinawa, particularly the late Middle Pleistocene sections of reef limestones exposed in southern Okinawa Island (Minatogawa Formation).
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