堆積有機物の炭素・窒素安定同位体比による古海洋解析 Paleoceanographic Analyses Using Stable Carbon and Nitrogen Isotopic Ratios of Sedimentary Organic Matter

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Recently stable carbon and nitrogen isotopic ratios (δ<SUP>13</SUP>C and δ<SUP>15</SUP>N) of the sedimentary organic matter have become to be applied to reconstruct past changes of the biogeochemical processes in surface waters, although they were used only as the mixing tracers of terrestrial organic matter into coastal sediments during 1970's and 80's. While both of the δ<SUP>13</SUP>C and δ<SUP>15</SUP>N values of the organic matter produced in the surface water change due to the isotopic fractionation processes during the uptake of inorganic substance (CO<SUB>2</SUB> and NO<SUB>3</SUB><SUP>-</SUP> etc.) by phytoplankton, the reconstructed paleoceanograhic factors are completely different between the δ<SUP>13</SUP>C and δ<SUP>15</SUP>N, such as the [CO<SUB>2</SUB>] <SUB>aq</SUB> and the phytoplankton growth rate for the δ<SUP>13</SUP>C and the nitrate availability for δ<SUP>15</SUP>N, reflecting the difference in Σ CO<SUB>2</SUB> and nitrate budgets in the sea surface water.<BR>Because the magnitude of carbon isotopic fractionation during the photosynthesis of phytoplankton are influenced by [CO<SUB>2</SUB>] <SUB>aq</SUB> in the surface water, many recent studies of the organic δ<SUP>13</SUP>C in the sediment cores discuss about past changes in pCO<SUB>2</SUB> in the surface water. However, the phytoplankton growth rate also governs the δ<SUP>13</SUP>C values of phytoplankton, andtherefore, it is actually very difficult to extract purely the [CO<SUB>2</SUB>] <SUB>aq</SUB> data from the organic δ<SUP>13</SUP>C values. On the other hand, δ<SUP>15</SUP>N of sediment is now believed to reflect the past changes in nitrate utilization rates in the surface water (<I>i.e.</I> biological pumping efficiency). Because the isotope fractionation during the nitrate uptake by phytoplankton makes theδ<SUP>15</SUP>N values of the remaining nitrate much higher in the surface water body, the relativelylow δ<SUP>15</SUP>N values of organic matter can be used to trace a upwelling center of the surface water.<BR>The δ<SUP>13</SUP>C and δ<SUP>15</SUP>N values in the particulate organic matter change largely during their sinking and sedimentation processes. Both of the two isotopic values in the sinking particledecrease downward irrespective of their sample sites, probably due to the selective decomposition of amino acids which have relatively higher δ<SUP>13</SUP>C and δ<SUP>15</SUP>N values than the bulk organic matter. Contrary to this, the δ<SUP>13</SUP>C and δ<SUP>15</SUP>N values increase again on the sediment surface. Because the changes in δ<SUP>13</SUP>C and δ<SUP>15</SUP>N values of organic matter in the sinking and sedimentation processes are universal and somewhat constant processes, it seems reasonable to apply the downcore δ<SUP>13</SUP>C and δ<SUP>15</SUP>N variations to reconstruct the past changes in the surface water processes.

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各種コード

  • NII論文ID(NAID)
    10002237564
  • NII書誌ID(NCID)
    AN00322536
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    0022135X
  • NDL 記事登録ID
    4480489
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z15-169
  • データ提供元
    CJP書誌  CJP引用  NDL  NII-ELS  J-STAGE 
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