| Research Abstract |
The object of this work is to reconstruct the change of ocean environment after the last glacial age. For this purpose, one sediment core was obtained using a piston corer near the summit of Shaisky Rise, one of isolated sea mounts located in the temperate region (32*, 1580* ; the depth of 2680 in). The age of this core was determined by the oxygen isotope curve measured by Dr. Oba of Hokkaido Univ. The age of the deepest layer, at the depth of 295 cm, was estimated to be ca. 260 ka B.P.The chemical analysis was performed for calcium carbonate, opaline silica and organic carbon as the proxy of the change of biomass production, iron, aluminum, titanium, manganese, copper, vanadium, barium and phosphorus as that of the aeorian dust flux, thorium isotopes (Th-230 and Th-232) as that of particle rain rate in the water column, and uranium isotopes (U-238 and U-234) as that of redox condition in the sedimentary environment.
The concentration changes of lithogenic elements as iron, aluminum, titanium and vanadium are little in the core. The elemental ratios to aluminum are fairly constant. These findings show that these elements are not concerned in the biological process in the surface water. The concentrations of biogenic calcium carbonate, opaline silica and organic carbon are relatively high in the warm ages, at 120 ka B.P.and the present time. The excess thorium-230 is also enriched in the layers corresponded to the post-glacial age. Consequently, we can suggest that the surface water biomass production in the warm age is rather higher than in the glacial age.
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