1998 Fiscal Year Final Research Report Summary
Analysis of the relationship between development of the Monsoon-induced upwelling and calcareous nannoflora
| Project/Area Number |
09640553
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | HOKKAIDO UNIVERSITY |
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Principal Investigator |
OKADA Hisatake Grad.School of Sci., Hokkaido Univ., Prof., 大学院・理学研究科, 教授 (80111334)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Calcareous nannofossil / Paleoenvironment / Quaternary / Indian Ocean / Monsoon |
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| Research Abstract |
Because of the SW Monsoon, strong upwelling develops at the off coast of Arabian Peninsula, but the monsoon strength is postulated to be significantly weakened during glacial periods. In order to understand the relationship between the flora and the Quaternary climate, calcareous nannofossils were studied at a site where a strong coastal upwelling develops (Core 723A) and at another site where a moderate upwelling occurs (Core 722A&B). In the sequence representing the last 270 Ky. At Core 723A, the stratigraphic change in relative abundance of the lower-photic dweller Florisphaera profunda is concordant with that of delta ^<18>O.The stratigraphic trend, increasing in the interglacial periods, however is contradictory to the Molfino and Mcintyre Model that says the abundance drops in a vertically mixing photic zone. Moreover, although a cold Gephyrocapsa species sharply increased in the middle part of the glacials, a warm Gephyrocapsa species took over the dominance during the glacial maximums.
Between 1.0 and 0.2 Ma at Site 722, the relative abundance of F.profunda increased during the glacials, but the trend is a complete opposite for the last 20 m.y., as was observed at Site 723. As expected, small placoliths that are common in the tropical Pacific upwelling exhibited a reversed trend in their stratigraphic variation with that of the warm Gephyrocapsa species. There is, however, no obvious relationship between these records and the stratigraphic variation of F.profunda. The observed changes in calcareous nannofossil are not concordant with the general trend of glacial/interglacial cycles
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