1998 Fiscal Year Final Research Report Summary
Study on paleoenvironmental changes recorded in the calcareous-siliceous sediments since ha last glacial maimum
| Project/Area Number |
08404030
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Kumamoto University |
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Principal Investigator |
ODA Motoyoshi Kumamoto University, Faculty of Science, Professor, 理学部, 教授 (60108454)
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| Co-Investigator(Kenkyū-buntansha) |
IRYU Yasufumi Tohoku University, Faculty of Sci., Assistant Prof., 理学部, 助手 (00250671)
XU Xeudong Kumamoto Univ., Faculty of Sci., Assistant Prof., 理学部, 助手 (70274686)
IWASAKI Yasuhide Kumamoto Univ., Faculty of Sci., Professor, 理学部, 教授 (40013750)
MATSUDA Hiroki Kumamoto Univ., Faculty of Sci., Associted Prof., 理学部, 助教授 (80274687)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Calcareous-siliceous sediments / Last Glacial Maximum / AMSC-14 age detemination / planktic foraminifera / Paleoenvironmental changes / Diagenesis / Oxygene-Carbon Isotope Analysis |
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| Research Abstract |
Planktic foraminiferal assemblages in 81 sea surface sediments from the Northwest Pacific Ocean were used to create ecological equations between foraminiferal abundaince variations and the present day surface water conditions near Japan. Principal factor analysis yielded five factors correlated with modern water masses : Kuroshio factor, Transitional Water factor, Oyashio factor, Kuroshio Gyre Margin factor and Coastal Water factor. These factors account for over 94% of the total variance (Takemoto & Oda, 1997). Furthermore, regression analysis produced transfer functions PFJ-125 relating observed winter and summer SST.The standard errors averaged about 1.75 degree (C) for winter SST, 1.l7 degree (C) for summer SST.PFJ-l25 were applied to planktic foraminiferal assemblages in seven cores obtained from the Kuroshio Region and two from Perturbed Area. These cores were dated by AMSl4C method. Factors and estimated SST indicate variations of the axis of the Kuroshio near Japan since 21k yr
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Furthermore, planktic foraminifera have been studied in two high-resolution AMS14C dated cores raised from the eastern East China Sea (ECS) in order to reconstruct the surface water history over the last 20,000 years. Three distinctively different planktic foraminiferal assemblages corresponding to the last glacial, deglacial and postglacial stages are recognized. The assemblage during the deglacial stage represented by high % frequency occurrence of G.quinqueloba and N.paclyderma (d) is quite different from those during the glacial and postglacial stages, showing unique character of the surface water environments during the last deglaciation : severely diluted and well stratified. The species association change indicates higher surface temperature and lower surface primary productivity during the postglacial stage than during the last glacial stage, and that the formation of the postglacial surface water circulation pattern in the eastern ECS was closely related to the flow of the Kuroshio current.
In addition, planktic foraminiferal assemblages in sea surface sediments from Sea of Japan are also analyzed to get the basic data between foraminiferal abundance variations and the present day surface water condition. Core recovered from mid of Sea of Japan was also dated by AMS 14C method.
To clarify the influence and time scale of early meteoric diagenesis on isotopic compositions of carbonate sediments, carbonate mineral compositions and values of 6 13C and 6 180 of the Holocene to Pleistocene carbonate sediments of the Ryukyuu Islands were analyzed. The data indicate that diagenetic alternation on mineral and isotopic compositions are within 4,000 yrs. after the deposition, and that serious changes of delta 13C and delta 18O from primary values occur within about a few ten thousand yrs. by early meteoric diagenesis. This suggested that the influence of meteoric diagenesis should not be ignored even if the sediments were deposoted only a few thousand years age, and that it is very important to carry out careful selections of samples and/or evaluations of data. Less
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Research Products
(18 results)
