| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Masanobu Hokkaido University, Graduate School of Environmental Science, Associate Professor, 大学院・地球環境科学研究科, 助教授 (60332475)
NAGAO Seiya Hokkaido University, Graduate School of Environmental Science, Associate Professor, 大学院・地球環境科学研究科, 助教授 (20343014)
OKADA Hisatake Hokkaido University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (80111334)
NARITA Hisashi Hokkaido University, Graduate School of Environmental Science, Assistant Professor, 大学院・地球環境科学研究科, 助手 (50250501)
IRINO Tomohisa Hokkaido University, Graduate School of Environmental Science, Assistant Professor, 大学院・地球環境科学研究科, 助手 (70332476)
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| Research Abstract |
The northwest Pacific, where the cold Oyashio and the warm Kuroshio Currents meet each other today, is the most sensitive region in the North Pacific for monitoring the migration of the western boundary corrects in response to the past climatic change. A long core (45.82 m length) was recovered from 2,224 m water depths off the central Japan during the IMAGES cruise in 2001. A multi-disciplinary study was carried out on the core by analyzing the following research items : color, grain size, mineral composition, paleomagnetism, δ^<18>O, δ^<13>C Opal, CaCO_3, species of diatoms, coccolithophorids, radiolaria, planktonic foraminifera and benthic foraminifera, CaCO_3 preservation, Uk37', TOC, C/N, δ^<13>C_<TOC>, δ^<15>N_<TOC>, biomakers and pollen. The following main results ware obtained. The δ^<18>O curve of G.bulloides is similar to the standard oxygen isotope curve, suggesting continuous deposition over the last 145 ka. All warm water indices yielded by the four microfossil assemblages (diatoms, coccolith, radiolaria, planktonic foraminifera) show temperature decreases during the MIS 2 and 6, and increases during the MIS 5, although their correlation coefficients with each other are not always high (between 0.5 and 0,6). The Alkenon-derived temperature (19℃) at the core top agrees with the mean annual SST at present time in this region. The SST at the end of the MIS 2 was 13℃, which is seen today about 4.5 degree latitude north than the core site. Similar migrations in SST are inferred from the coiling ratio of N.pachyderma. The C/N ratio, δ^<13>C_<TOC> and δ^<15>N_<TOC> indicate that the TOC is mainly of marine origin, although terrestrial origin slightly increases during the MIS 6. The curve of the warm pollen index is similar to the δ^<18>O curve of G.bulloides, except for the MIS 6 and 5e when the land temperature changes inferred from the pollen curve precede the δ^<18>O curve.
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