夏季の南極昭和基地周辺の定着氷下におけるクロロフィルα及び硝酸塩濃度の時間変化 Temporal changes in chlorophyll a and nitrate concentrations under fast ice near Syowa Station, Antarctica, in austral summer

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Abstract

1996年12月30日,1997年1月12日及び21日に,南極昭和基地周辺のリュツォ・ホルム湾の4点において,水深5mから海底の間の数層から海水試料を得た.得られた試料を基にクロロフィルa(Chl a)及び硝酸塩(NO3)濃度の鉛直分布を調べた.いずれの観測点においても表層の成層水中(<20m)でChl a及びNO3濃度が時間とともに大きく変化した.両濃度には有意な負の関係があった(n=40, P<0.01).この関係は,Chl aが1μg l-1増加するときNO3を0.89μM消費することを示唆する.しかしながら,本研究で見られたような厚い海氷(2.0-3.6m)下における光強度は,植物プランクトンが増殖するのに厳しい条件にある.本研究で観測されたChl aの増加が,植物プランクトンが厚い定着氷下で増殖した結果とは考えにくい.好光条件の下でChl aを増加させ,NO3を消費した海水が観測海域へ移流していたと考えられる.この移流が,厚い定着氷下で見かけ上Chl aが増加しNO3が低下する要因と思われる.

Seawater samples beneath fast ice were collected from several depths using a Niskin bottle at four sites near Syowa Station, Antarctica, on 30 December 1996, and 12 and 21 January 1997. Vertical distributions of chlorophyll a (Chl a) and nitrate (NO3) concentrations were determined. Substantial temporal changes in Chl a and NO3 concentrations occurred in the surface stratified layer (<20m). There was a significant negative correlation between both the concentrations (n=40, P<0.01). This relationship suggests that an increase of 1μg l-1 of Chl a consumes 0.89μM of NO3 under fast ice. However, light limitation is severe for phytoplankton growing under thick sea ice (2.0-3.6m), as observed in the present study. It is unlikely that the observed increases of Chl a result from phytoplankton growth under heavy fast ice. Seawater, in which Chl a has increased and NO3 has been consumed under favorable light conditions, may be advected into the study area. This advection may be responsible for the apparent increase of Chl a and decrease of NO3 concentrations under the heavy fast ice.

Journal

  • Antarctic record

    Antarctic record 48(3), 157-164, 2004-11

    National Institute of Polar Research

Codes

  • NII Article ID (NAID)
    110001063036
  • NII NACSIS-CAT ID (NCID)
    AN00181831
  • Text Lang
    ENG
  • ISSN
    00857289
  • NDL Article ID
    7274918
  • NDL Source Classification
    ZM1(科学技術--科学技術一般)
  • NDL Call No.
    Z14-316
  • Data Source
    NDL  NII-ELS 
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