CO 2 dynamics of the atmosphere and surface seawater in coastal zone

Abstract

To clarify the carbon dioxide CO 2 dynamics in the atmosphere and the surface seawater in the coastal regions, CO 2 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 CO 2 concentration in the atmosphere were continually measured at each station in Osaka Bay. The values of CO 2 in seawater were calculated using the CO 2 SYS by CDIAC. Air to sea CO 2 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 CO 2 absorption flux was high, and atmospheric CO 2 concentration was low. CO 2 flux had large diurnal change by daytime photosynthesis and nighttime respiration. In this period, mean CO 2 absorption flux was 0.09 g-C m 2 d 1 , and atmospheric CO 2 concentration was 397.7 ppm. On the other hand, in the autumn when the stratification disappears, mean CO 2 absorption flux was 0.04 g-C m 2 d 1 , and atmospheric CO 2 concentration was 429.9 ppm. In summer, surface water CO 2 fluctuation had large diurnal change by photo-synthesis, and atmospheric CO 2 is absorbed to surface seawater. In the autumn, CO 2 in seawater was release to the atmosphere. Therefore, the atmospheric CO 2 concentration changes largely by air to sea CO 2 flux.