Cyclic Fluctuation in the Differential Dissolution of Late Quaternary Diatoms in the Western Equatorial Pacific Ocean.

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  • Ikeda Akihiro
    Department of Earth and Planetary Science, Graduate School of Science, Hokkaido University

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  • 西赤道太平洋の第四紀後期珪藻遺骸群集に見られる選択的溶解作用の周期性
  • ニシ セキドウ タイヘイヨウ ノ ダイ4キ コウキ ケイソウ イガイ グンシュ

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Abstract

Paleoceanography based on diatom thanatocoenoses is marked by a gradual increase in diatom valves, which corresponds to Mid-Brunhes Climatic Events (MBCE), and 105yr order cycles driven by orbital forcing during the past 660kyr of ODP Hole 807A (Ontong Java Plateau). The gradual increase after 400ka may be the result not of changes in the state of dilution or dissolution, but of increased productivity, which is caused by enhanced circulation between high and low latitudes. For samples of the last 400kyr, principal component analysis was performed. The first component (as an index of dissolution) shows strong cyclicity, which is closely comparable to the climatic precession, and it is thought to be the result of east-to-west circulation inside the equatorial region rather than global circulation. Recent studies, involving some sediment-trap data, insist that major dissolution of diatom frustles does not occur through the water column but at the sea surface water-mass and at the surface of sediment. In this study, also taking into account those studies, limiting factors of dissolution in equatorial region are discussed, and it is concluded that cyclic dissolution reflects changes in surface currents and the changes of dissolved silica concentration in the sea surface watermass.

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