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Contribution of biological effects to carbonate-system variations and the air-water CO2 flux in inner and outer bays in Japan
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  • Tatsuki Tokoro,
  • Shin-ichiro Nakaoka,
  • Shintaro Takao,
  • Tomohiro Kuwae,
  • Atsushi Kubo,
  • Toru Endo,
  • Yukihiro Nojiri
Tatsuki Tokoro
National Institute for Environmental Studies

Corresponding Author:[email protected]

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Shin-ichiro Nakaoka
National Institute for Environmental Studies
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Shintaro Takao
National Institute for Environmental Studies
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Tomohiro Kuwae
Port and Airport Research Institute
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Atsushi Kubo
Shizuoka University
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Toru Endo
Osaka City University
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Yukihiro Nojiri
Hirosaki University
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We evaluated the contribution of biological effects (photosynthesis, respiration, and decomposition) to the carbonate parameters and air-water CO2 fluxes in Tokyo Bay, Ise Bay and Osaka Bay in Japan. The carbonate parameters were measured mainly by cargo ships travelling between Japan and other countries. We used the measurement data from three inner bays and surrounding outer bays in Japan along with reference data from previous studies for complementary analysis. We found that 1) the inner bays in this study were strong annual atmospheric CO2 sinks, 2) the annual biological effect on the air-water CO2 fluxes was about 5-25% of the measured CO2 fluxes and it affected the seasonal variation of the CO2 flux, and 3) the biological effect was largest in Tokyo Bay, and almost the same in Ise and Osaka Bays. The intensity of the biological effect corresponded mainly with nutrient concentrations, which seemed to be controlled by the wastewater treatment in urbanized areas around the bays. The CO2 flux was also affected by the seawater residence time, salinity, and stratification. Our results suggest that labile carbon/nutrient ratio of wastewater should be a major consideration for evaluating the biological effect on the carbon cycle in urbanized inner bays, which will continue to expand globally.