Seasonal and Interannual Variations in Nitrogen Availability and Particle Export in the Northwestern North Pacific Subtropical Gyre

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  • Y. Mino
    Institute for Space‐Earth Environmental Research Nagoya University Nagoya Japan
  • C. Sukigara
    Center for Marine Research and Operations Tokyo University of Marine Science and Technology Tokyo Japan
  • M. C. Honda
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • H. Kawakami
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • M. Wakita
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • K. Sasaoka
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • C. Yoshikawa
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • O. Abe
    Graduate School of Environmental Studies Nagoya University Nagoya Japan
  • J. Kaiser
    Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences University of East Anglia Norwich UK
  • K. Kimoto
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • M. Kitamura
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • T. Fujiki
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • K. Matsumoto
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan
  • T. Saino
    Japan Agency for Marine‐Earth Science and Technology Yokosuka Japan

書誌事項

公開日
2020-05
資源種別
journal article
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1029/2019jc015600
公開者
American Geophysical Union (AGU)

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説明

<jats:title>Abstract</jats:title><jats:p>Time series of particulate nitrogen isotope delta (PN‐<jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N) and flux of trapped particles at 200 m were determined in the northwestern North Pacific subtropical gyre between 2010 and 2014 in order to examine temporal variations in mixed layer nitrate availability and downward particle export. Lower PN‐<jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N (<4‰) seen every winter corresponded to convective nitrate supply triggering phytoplankton blooms. Greater particle fluxes were associated with higher CaCO<jats:sub>3</jats:sub> concentrations (mass fraction >50%), implying that new nitrogen supply stimulated predominantly coccolithophore growth and downward transport of coccoliths. Even in the stratified summer of 2011, a <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N drop associated with a spike in particulate flux was found and was attributed to the uplift of nitrate‐rich deep waters due to a mesoscale cyclonic eddy passing the mooring station. Total nitrate input sustains 86–93% of annual new production in this region while nitrogen fixation accounts for the rest. Trapped particles also showed that the winter <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N decrease appeared earlier in the 2011–2012 blooms than those in 2013–2014, coinciding with 8% higher CaCO<jats:sub>3</jats:sub> concentrations and a 40% lower particulate organic carbon to inorganic carbon export ratio, <jats:italic>R</jats:italic>(POC:PIC). This reflected stronger convective mixing and hence larger nutrient supply in 2011–2012, caused by larger ocean heat loss related to winter monsoon intensity. Such interannual change of winter <jats:italic>R</jats:italic>(POC:PIC) can affect CO<jats:sub>2</jats:sub> uptake rate in the northwestern North Pacific subtropical gyre where anthropogenic CO<jats:sub>2</jats:sub> accumulates in subtropical mode waters.</jats:p>

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