Late Quaternary Paleoceanography in the Northwestern Pacific Margin Reconstructed with a Submarine Core Recovered Off Sanriku. An Approach Using Diatom Fossil Assemblage.

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  • Shimada Chieko
    Graduate School of Environmental Earth Science, Hokkaido University
  • Hasegawa Shiro
    Graduate School of Environmental Earth Science, Hokkaido University

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Other Title
  • 三陸沖海底コアを用いた第四紀後期の北西太平洋縁辺域における古海況　　珪藻化石群集からのアプローチ
  • サンリクオキ カイテイ コア オ モチイタ ダイ4キ コウキ ノ ホクセイ タイヘイヨウ エンペンイキ ニ オケル コ カイキョウ ケイソウ カセキ グンシュウ カラ ノ アプローチ
  • An Approach Using Diatom Fossil Assemblage
  • 珪藻化石群集からのアプーチ

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Abstract

A Q-mode principal components analysis (PCA) based on downcore variation of diatom fossil assemblage was carried out in order to reveal the late Quaternary paleoceanography of the NW Pacific margin with the qualified submarine core KH 94-3, LM-8, recovered off the Sanriku coast, NE Japan.<br>It is recognized that increase of diatom valve concentration (DVC: valves/g) occurred in oxygen isotopic Stage 3 (interstadial during the last glacial) and Stage 1 (Holocene). However, diatom assemblages show drastic change between the two periods. As the result of PCA, we delineated four principal components explaining 93.6% of total variance. Principal compoent 1 is composed mainly of Thalassionema nitzschioides (Grunow) H. et M., which dominates in the coldest Stages 4 and 2 with diatom valves being poorly preserved and DVC being the lowest. Principal component 2 with some ice-related diatoms predominates in Stage 3, whereas principal component 3, which is characterized by Neodenticula seminae (Simonsen et Kanaya) Akiba et Yanagisawa and Odontella aurita (Lyngbye) Agardh, displays high values in Stage 1.<br>Here, we suggest that intensified discharge of sea ice originated in the Sea of Okhotsk in Stage 3. This interpretation subsequently enables us to explain the high DVC during the period as being due to high productivity at the sea ice edge. We can also infer that the qualitative difference in the Oyashio between the glacial and the interglacial is due to change in the supplying mode of the Okhotsk-originating factor such as sea ice, and consequently that there is a different mechanism of high primary productivity in the area off Sanriku during each period.

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