Journal of Oceanography

, Volume 61, Issue 1, pp 129–139 | Cite as

Temporal Change of Dissolved Inorganic Carbon in the Subsurface Water at Station KNOT (44°N, 155°E) in the Western North Pacific Subpolar Region

  • Masahide Wakita
  • Shuichi Watanabe
  • Yutaka W. Watanabe
  • Tsuneo Ono
  • Nobuo Tsurushima
  • Shizuo Tsunogai


The dissolved inorganic carbon (DIC) and related chemical species have been measured from 1992 to 2001 at Station KNOT (44°N, 155°E) in the western North Pacific subpolar region. DIC (1.3∼2.3 µ mol/kg/yr) and apparent oxygen utilization (AOU, 0.7∼1.8 µmol/kg/yr) have increased while total alkalinity remained constant in the intermediate water (26.9∼27.3σθ). The increases of DIC in the upper intermediate water (26.9∼27.1σθ) were higher than those in the lower one (27.2∼ 27.3σθ). The temporal change of DIC would be controlled by the increase of anthropogenic CO2, the decomposition of organic matter and the non-anthropogenic CO2 absorbed at the region of intermediate water formation. We estimated the increase of anthropogenic CO2 to be only 0.5∼0.7 µmol/kg/yr under equilibrium with the atmospheric CO2 content. The effect of decomposition was estimated to be 0.8 ± 0.7 µmol/kg/yr from AOU increase. The remainder of non-anthropogenic CO2 had increased by 0.6 ± 1.1 µmol/kg/yr. We suggest that the non-anthropogenic CO2 increase is controlled by the accumulation of CO2 liberated back to atmosphere at the region of intermediate water formation due to the decrease of difference between DIC in the winter mixed layer and DIC under equilibrium with the atmospheric CO2 content, and the reduction of diapycnal vertical water exchange between mixed layer and pycnocline waters. In future, more accurate and longer time series data will be required to confirm our results.


Dissolved inorganic carbon temporal change anthropogenic CO2 western North Pacific subpolar region 


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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Masahide Wakita
    • 1
    • 2
  • Shuichi Watanabe
    • 1
    • 2
  • Yutaka W. Watanabe
    • 1
  • Tsuneo Ono
    • 4
  • Nobuo Tsurushima
    • 3
  • Shizuo Tsunogai
    • 1
  1. 1.Graduate School of Environmental Earth ScienceHokkaido UniversitySapporoJapan
  2. 2.Japan Agency for Marine-Earth Science and TechnologyYokosukaJapan
  3. 3.National Institute for Advanced Industrial Science and TechnologyTsukubaJapan
  4. 4.Hokkaido National Fisheries Research InstituteKushiroJapan

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