Holocene paleoenvironment in the SW part of the Sea of Okhotsk : an interpretation based on diatom fossil analysis

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  • オホーツク海南西部における完新世の古環境 : 珪藻化石分析から

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Diatom fossil analysis was carried out in order to reveal Holocene paleoenvironment in the SW part of the Sea of Okhotsk using the quarified piston core HS97,P1 recovered off Shiretoko Peninsula, eastern Hokkaido. It should be emphasized that there are very few investigations for diplomatic problems even though oceanographic factors can be expected to reflect global environmental change and affect human activities. As the results, we recognized that occurrence of Thalassionema nitzschioides and Neodenticula seminae, both of which indicate high productivity, increased toward the top of the core, whereas those of ice-related, allochthonous and brakish species decreased. Besides we ditected the cyclic occurrence of warm water species Fragilariopsis doliosus as a sensitive indicator of the Soya Warm Current in spite of low frequencies. Concequently we described the following scenario based on the obtained results : 1)There has existed sea ice concentration off Shiretoko for the last 7400 years with its intensity diminishing, 2)The cyclic occurrence of F. doliosus is likely to tuned to the pulses of the Tsushima Warm Current in the Sea of Japan during Holocene outlined in Koizumi (1987,1994), in addition to the time-space distribution of warm molluscan fossils such as Meretrix lusoria in some shell mounds around eastern Hokkaido.

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