ラニーニャ時のレディオラリアフラックス : 1999年太平洋赤道域西部・中部における時系列変動と海洋環境 Temporal and vertical flux changes of radiolarians in the western and central equatorial Pacific during the 1999 La Nina conditions

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著者

    • 高橋 孝三 Takahashi Kozo
    • 九州大学大学院理学研究院地球惑星科学部門 Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University
    • 山下 仁司 Yamashita Hitoshi
    • 九州大学大学院理学府地球惑星科学専攻 Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University

抄録

太平洋赤道域西部・中部には,年間を通して高水温の西太平洋暖水塊(WPWP)が,その東部には赤道湧昇域(EUR)が存在し,エルニーニョ時にはWPWPが東に移動することにより大気系に異常をきたす.これまでのEl Nino-Southern Oscillation(ENSO)の解明を通じて,WPWPが地球の気候システムの熱源・水蒸気源となっていることが分かっており,本海域は地球規模の気候変動を解明する上で重要な海域である.本研究では,珪質動物性プランクトンのレディオラリア群集沈降粒子フラックスを用いて海洋環境変動の考察を行った.その結果,種組成変化をSite間で比較すると,WPWP海域に比べ,Lithomelissa setosa, Pseudocubus obeliscus, Lophophaena cylindrica等の種がEUR海域でフラックス,割合ともに増加する違いが現れた.レディオラリアを用いた古環境復元には,生産から堆積物中埋没までの一連の鉛直輸送と保存過程の包括的な理解が必要で,沈降粒子フラックスに加えプランクトンネット,マルチプルコア試料を併用し,種組成変化の観点から一連のプロセスを考察した.

Temporal flux changes of radiolarians were investigated employing tune-series sediment traps deployed in the western and central equatorial Pacific during January to November 1999. On board R/V Mirai the sediment traps were deployed at four sites located between 135°E and 175°E, i.e., across the western Pacific warm pool (WPWP) region and the Equatorial Upwelling region (EUR). Total radiolarian fluxes showed higher values at Sites MT1, 2, 5 than that at Site MT3. Radiolarian production reflected levels of biological productivity, i.e., the levels of nutrient supply. The radiolarian flux species compositions at each site did not vary much seasonaly whereas levels of total radiolarian flux varied significantly. Several useful environmental indicator species are presented in this study. For instance, Lithomelissa setosa and Pseudocubus obeliscus are good eutrophic indicators. They are important tracers of the present WPWP migration in the western and central equatorial Pacific. The flux pattern of Lophophaena cylindrica was nearly the same as that of total radiolarians, and this species could represent the whole radiolarian productivity in the western and central equatorial Pacific. Furthermore, in order to understand the vertical radiolarian transport, the sediment trap samples were com-pared with the samples from plankton tows as well as core tops obtained using a multiple corer. The changes of Nassellaria-Spumellaria ratios between the suspended and sinking radiolarian populations were not significant, but there were significant differences between the sinking and surface sediment populations. It suggested that in the western and central equatorial Pacific the significant dissolution of radiolarians took place in surface sediments. The radiolarian assemblages were affected by selective dissolution. It appears that every species receives different levels of dissolution during their vertical transportation. The results provide important information when radiolarian microfossils are used to reconstruct paleoceanographic conditions.

収録刊行物

  • 地質學雜誌

    地質學雜誌 110(8), 463-479, 2004-08-15

    日本地質学会

参考文献:  59件中 1-59件 を表示

被引用文献:  2件中 1-2件 を表示

各種コード

  • NII論文ID(NAID)
    110003009869
  • NII書誌ID(NCID)
    AN00141768
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    00167630
  • NDL 記事登録ID
    7078867
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質)
  • NDL 請求記号
    Z15-174
  • データ提供元
    CJP書誌  CJP引用  NDL  NII-ELS  J-STAGE 
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