1995 Fiscal Year Final Research Report Summary
Late Quaternary changes of warm current system in the northwestern Pacific Ocean from the equator to the Ryukyu Island Arc region.
| Project/Area Number |
05455019
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
広領域
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| Research Institution | UNIVERSITY OF THE RYUKYUS |
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Principal Investigator |
UJIIE Hiroshi Univ.of the Ryukyus, Dept.of Marine Scis., Professor, 理学部, 教授 (60000113)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Toshio Dating & Material Research Center, Nagoya Univ., Associate Professor, 年代測定資料センター, 助教授 (10135387)
ONO Tomonori Univ.of the Ryukyus, Dept.of Marine Scis., Research Assistant, 理学部, 教務職員 (70233583)
YAMAMOTO Satoshi Univ.of the Ryukyus, Dept.of Marine Scis., Lecturer, 理学部, 講師 (50124855)
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| Project Period (FY) |
1993 – 1995
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| Keywords | Ryukyu Trench slope / piston core / Kuroshio Current / Benthic foraminifera / Oxygen / carbon isotope ratio / Central to southern Ryukyu land bridge / Florisphaera profunda / pulleniatina group |
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| Research Abstract |
1) Variable analyzes of three piston cores taken from the Ryukyu Trench slope area revealed that down-core change of Florisphaera profunda, a calcareous nannoplankton, indicate sea-water turbidity (=primary production) change during the late Quaternary. 2) Prototypes of the Okinawa Trough and the Ryukyu Island Arc appeared during the Middle Pleistocene. Afterward, the Kuroshio Current has entered into the Trough. 3)Benthic foraminiferal changes in two cores taken from the south of Ishigaki Island reflected bottom water changes during the past 210 ka. 4) To more precisely understand the faunal change through sedimentary sequences, the detailed and multivariate analyzes of Recent benthic foraminiferal assemblages were completed for a coral reef area (62 sediment samples used) and for the batyal environment (56 real surface samples used). 5) To know the relationship between sedimentary materials carried by the Kuroshio Current and by Asiatic continental rivers during the post-glacial period, nine cores were collected from the Okinawa Trough and investigated by variable methods.Only a terrigenous plant fragment supply indicate steady decrease toward Recent according to the down-core changes of organic carbon/nitrogen ratio and lignin-phenol content. This means the gradual disappearance of a land-bridge connected Taiwan through Okinawa to Amami-ohshima during the last glacial episode. This disappearance mode was supported by a upward increase of pulleniatina group, planktonic foraminifera characteristic of the Kuroshio Current. This group suddenly disappeared during a few hundred years at - 3,800 yr.BP., suggesting a temporary formation of the above land-bridge or of similar situation.
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