NUMERICAL MODELING OF CO₂ DYNAMICS IN SEAWATER CONSIDERING EFFECTS OF FRESHWATER INFLOW IN THE YATSUSHIRO SEA

Abstract

 Regarding the reduction of atmospheric CO₂, the function of CO₂ absorption in coastal areas has been drawing attention. In this study, we developed a numerical model of pCO₂ dynamics considering effects of freshwater inflow based on the results of field observation in the Yatsushiro Sea, to obtain the basic knowledge about CO₂ dynamics in coastal areas. The model was able to reproduce well the tempo-spatial distribution of pCO₂ and the distribution of salinity and water temperature under different stratification conditions. From the results of the hindcast simulation, it was confirmed that the amount of CO₂ absorbed around the estuary fluctuated greatly spatiotemporally with the big flood. Furthermore, the following two effects of the freshwater inflow on the dynamics of CO₂ in the coastal area are confirmed as follows: i) After flooding, CO₂ release can be promoted by the suface freshwater capping; and ii) After mixing of freshwater and seawater, CO₂ absorption can be promoted by photosynthesis due to blooming of phytoplankton in the surface layer.