1997 Fiscal Year Final Research Report Summary
Reconstruction of paleoceanographic changes in the Japan Sea in response to centennial to millennial-scale global climatic changes
| Project/Area Number |
08458141
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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 |
Environmental dynamic analysis
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| Research Institution | University of Tokyo |
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Principal Investigator |
TADA Ryuji University of Tokyo, Graduate School of Science, Associate Professor, 大学院・理学系研究科, 助教授 (30143366)
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| Co-Investigator(Kenkyū-buntansha) |
KOIZUMI Itaru Hokkaido University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (20029721)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Japan Sea / Late Quaternary / Paleoceanography / Dansgaard Cycles / Aeolian Input |
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| Research Abstract |
This research is aimed to clarify paleoceanographic changes of the Japan Sea in association with centennial to milennial-scale global climatic changes known as Dansgaard-Oeschger [D-O] Cycles through the high resolution analysis of piston cores retrieved from the deeper partrs of the Japan Sea. Two piston cores KT 94-15-PC-5 and PC-9 which were retrieved from the sites off Akita were used for analyzes of bulk chemistry, bulk mineralogy, sedimentary structures such as lamination and bioturbation, and diatom assemblage. Based on the results of these analyzes, character of the surface water, bottom water oxygenationlevel, and contribution of aeolian flux from the continent were evaluated. By examining temporal and spatial changes of these parameters, weinvestigated a) how character of the surface water and oxygenation level of the deep water had been changed in response to D-OCycles, b) what the phase relationship between these two parameters and D-O Cycles was, and c) what the phase rela
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tionship of between aridity changes in inland East Asia deduced from the contribution of aeolian materials and D-O Cycle was.
The results suggest 1) the dark layrs in the Japan Sea sediments correlate to interstadials of D-O Cycles, 2) the dark layrs always preserve parallel laminations which suggests deposition under suboxic to euxinic bottom water conditions, 3) sudden increases in contribution of aeolian materials generally coincide with but sometimes lead or lag by one sample (c. a. 600 yrs) from the start of deposition of the dark layrs, and 4) the linear sedimentation rates of the dark layrs tend to be slower than the adjacent light layrs and consequently aeolian flux also seems to have been smaller in the dark layrs than in the adjacent light layrs. The observed phase shift of one sample (c. a. 600 yrs) between the start of the dark layrs deposition and the increase in aeolian contribution could be attributed to the fact each sample represent a 2.5cm stratigraphic interval and sometimes cover the boundary between the dark land light layrs. The possible phase lag of aeolian contribution decrease behind the start of deposition of the dark layrs by as much as 3000 yrs previously pointed out by us based on the analyzes of 1500 yrs interval samples from ODP Site 797 seems to be suppositional and caused by coarse and not continuous sampling. Less
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