Comparative paleoceanographical study using piston cores from Okhotsk Basin and Suiko Sea Mount

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The object of this work is to reconstruct the change of paleo-environment after the last glacial age. For this purpose, two sediment cores were obtained using a piston corer in the Okhotsk Basin (12.8 m length) and at near the summit of Suiko Sea Mount (13.5 m length), which is one of the Emperor Sea Mounts. In the Okhotsk core, reduced suifur, biogenic opal and elemental composition of sediment were determined. In the Suiko core, biogenic carbonate and elemental composition of sediment were determined.In the Okhotsk core, the content of biogenic opal, as well as biogenic barium, was higher in the upper layer and gradually decreases with downcore, and has a maximum in the layer of 8-10 m depth, corresponding to the last glacial maximum age. Below the layer, the content of reduced sulfur gradually increases with downcore. These findings suggest that the biological production in the Okhotsk Sea is rather lower in the glacial period than in the interglacial age. On the other hand, the distributions of lithogenic elements, iron, titanium, aluminum, calcium and magnesium, were uniform in the upper interglacial period, but rapidly increased with downcore below the depth of 8-10 m. This implies that such the change of elemental composition of the sediment result from the greater supply of ice-rafted detritus in the last glacial maximum age.In the Suiko core, the concentration of biogenic carbonate varies from 4% to 94%, and the average was 69% in the whole core. The age of the layer of 2.5 m depth is estimated to 120 kyr B.P. on the basis of Narita et al. (2002). Therefore, it is suggested that the biological production in this area also has decreased during the last glacial age.