1994 Fiscal Year Final Research Report Summary
HIGH RESOLUTION CYCLESTRATIGRAPHY BASED ON DARK ANDLITGT COLOR-BANDED CLAYLAYERS
| Project/Area Number |
04402014
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | HOKKAID UNIVERSITY |
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Principal Investigator |
KOIZUMI Itaru HOKKAIDO UNIVERSITY,FACULTY OF SCIENCE,PROFESSOR, 理学部, 教授 (20029721)
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| Co-Investigator(Kenkyū-buntansha) |
TADA Ryuji UNIVERSITY OF TOKYO,GEOLOGICAL INSTITUTE A.PROFESSOR, 大学院・理学系研究科, 助教授 (30143366)
NAKAGAWA Mitsuhiro HOKKAIDO UNIVERSITY,FACULTY OF SCIENCE,ASSISTANT, 理学部, 助手 (50217684)
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| Project Period (FY) |
1992 – 1994
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| Keywords | JAPAN SEA / DARK AND LIGHT LAYERS / EUSTATIC SEALEVEL CHANGES / TSUSIMA WARM CURRENT / MILANKOVICH CYCLE / DANSGAAR-OESCHGER OSCILATION / ODP / EAST CHINA SEA COASTAL WATER |
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| Research Abstract |
LATE QUATERNARY SEDIMENTS RECOVERED BY THE ODP LEG127 FROM THE BASINAL SITES OF THE JAPAN SEA ARE CHARACTERIZED WITH DISTINCTLY DARK AND LIGHT COLOR-BANDED CLAY.THICKNESS OF THE DARK AND LIGNT LAYERS VARIES FROM A CENTIMETER TO MORE THAN 2 METERS.THESE DARK AND LIGHT LAYERS ARE CORRELATABLE AND SYNCHRONOUS BASIN WIDE,SUGGESTING THEY RECORD SOME SORT OF REGIONAL OR GLOBAL PALEOENVIRONMENTAL CHANGES TO WHICH THE JAPAN SEA RESPONDED AS A SINGLE SYSTEM.IN ORDER TO UNDERSTAND THE IMPLICATION OF THESE DARK AND LIGNT LAYERS,WE ANALYZED LATE QUATERNARY SAMPLES.
INFLOW OF THE TSUSIMA WARM CURRENT THROUGH THE TSUSIMA STRAIT WAS SIGNIFICANT DURING SEA LEVEL HIGHSTANDS WHEN HIGH SALINITY OF THE SURFACE WATER OF THE JAPAN SEA ALLOWED INTENSIVE DEEP WATER PRODUCTION AND VENTILATION OF THE BOTTOM.DURING INTERMEDIATE STANDS,THE EAST CHINA SEA COASTAL WATER PROPAGATED TO THE MOUTH OF THE TSUSIMA STRAIT AND FLOWED INTO THE SEA.DUE TO ITS LOWER SALINITY,THE INFLOW OF THE COASTAL WATER CAUSED WEAK DENSITY STRATIFICATION AND SUBDUED PRODUCTION OF DEEP WATER,WHICH RESULTED IN ANOXIC TO EUXINIC BOTTOM WATER CONDITION.DURING THE VERY LOWSTANDS,THE JAPAN SEA WAS NEARLY ISOLATED AND THE SURFACE WATER SALINITY DRASTICALLY DECREASED,CAUSING STRONG DENSITY STRATIFICATION,WHICH RESULTED IN STABLE EUXINIC BOTTOM WATER CONDITION.
HIGH RESOLUTION ANALYSES OF THE DARK AND LIGHT LAYERS SUGGESTED THAT MILANKOVICH CYCLE RESULTING FROM THE EARTHS ORBITAL ELEMENTS AS WELL AS DANSGAARD-OESCHGER OSCILLATION REPORTED FROM GREENLAND ICE CORES ARE RECORDED IN THE JAPAN SEA SEDIMENTS AS VARIATION IN ORGANIC CARBON CONTENT,DIATOM ABUNDANCE CHANGES,AND CHANGES IN KOSA FRACTION WITHIN DETRITAL COMPONENT.IT WAS ALSO SUGGESTED THAT PALE-OCEAN CIRCULATION HAS BEEN MOST SENSITIVE TO SEA LEVEL CHANGES DURING INTERMEDIATE STANDS.
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