To clarify the carbon dioxide (CO2) dynamics in the atmosphere and the surface seawater in the coastal regions, CO2 has been continuously measured in Osaka Bay from August to November, 2012 and 2014. Water temperature, dissolved oxygen (DO) and pH in the surface seawater, and the CO2 concentration in the atmosphere were continually measured at each station in Osaka Bay. The values of CO2 in seawater were calculated using the “CO2SYS” by CDIAC. Air to sea CO2 flux was calculated from these data and wind speed measured at Kobe airport by Japan Meteorological Agency. Consequently, during the stratified period of summer, the CO2 absorption flux was high, and atmospheric CO2 concentration was low. CO2 flux had large diurnal change by daytime photosynthesis and nighttime respiration. In this period, mean CO2 absorption flux was 0.09 g-C m-2 d-1, and atmospheric CO2 concentration was 397.7 ppm. On the other hand, in the autumn when the stratification disappears, mean CO2 absorption flux was -0.04 g-C m-2 d-1, and atmospheric CO2 concentration was 429.9 ppm.
In summer, surface water CO2 fluctuation had large diurnal change by photosynthesis, and atmospheric CO2 is absorbed to surface seawater. In the autumn, CO2 in seawater was release to the atmosphere. Therefore, the atmospheric CO2 concentration changes largely by air to sea CO2 flux.
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