| Project/Area Number |
17340153
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | Tohoku University |
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Principal Investigator |
YAMADA Tsutomu Tohoku University, Graduate School of Science, Tohoku University, Assistant Professor (50321972)
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| Co-Investigator(Kenkyū-buntansha) |
IRYU Yasufumi Graduate School of Science, 大学院・理学研究科, Associate Professor (00250671)
YOSHIMURA Kazuhisa Graduate School of Sciences, Kyusyu University, Professor (80112291)
AIZAWA Shoichi Faculty of Engineering, Gunma University, Associate Professor (20008527)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥15,470,000 (Direct Cost: ¥15,200,000、Indirect Cost: ¥270,000)
Fiscal Year 2007: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2006: ¥6,800,000 (Direct Cost: ¥6,800,000)
Fiscal Year 2005: ¥7,500,000 (Direct Cost: ¥7,500,000)
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| Keywords | environmental change / giant clam / growth band / paleo-insolation / paleotemperature |
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| Research Abstract |
To reconstruct daily paleoenvironmental changes in tropical-subtropical regions using tridacnid shells, we developed analytical methods of the shells and attempted to reveal quantitative relationships between carbon and oxygen isotope compositions, daily growth rate and elements/calcium ratios, and growth environments. Then we applied our results to fossil tridacnid shells and try to reconstruct paleoenvironmental changes.
Shell materials of tridacnid shells formed in the first decade of life are suitable for daily environmental reconstruction because growth rate of the shells decrease sharply at around 10 years after birth. Carbon and oxygen isotopic profiles in three skeletal regions (inner layer, outer layer and hinge area) are very similar, and all regions are formed at oxygen isotopic equilibrium with ambient seawater. Isotopic compositions of the shell materials at daily resolution are enable to analyze using new sampling methods with a micro-dissector. Major factors controlling daily growth rate of the shells are revealed to be water temperature and amount of isolation, but contributing structure of the two factors are difficult to resolve at this time. Mg/Ca and Sr/Ca ratios of carbonate reference material (JCt-1) and a fossil tridacnid shell from Ishigaki-jima are analyzed using ICP-AES with double spectrometers. The ratios do not exhibit a clear seasonal cycle and are extremely low compared to those of reef-building corals that form calcareous skeletons out of isotopic equilibrium. Calcification process of tridacnid is expected to be different from that of reef-building corals.
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