Ocean Acidification

Recently carbon dioxide fluxes between sea water and air have been measured in many coastal seas to clarify whether the coastal seas are source or sink of CO2. In this study behavior of CO2 within the water column is studied in a semi-enclosed coastal sea: the Seton Inland Sea, Japan. It was found that seasonal formation of hypoxic water mass is highly related to CO2 dynamics in coastal seas. Bacterial remineralization of organic matter consumes dissolved oxygen (DO) and releases dissolved CO2 in the bottom water when summertime thermal stratification develops. The CO2 accumulates within the low-DO bottom water (hypoxic water) and causes increasing of carbonic acid content which results low pH. Concentration of dissolved CO2 and pH are linearly correlated with DO concentration. The summertime low-DO and acidification (low pH) occur in the lower layer in every year. The accumulated CO2 during summer season is dispersed to the upper layer at the beginning of mixing season.



Taguchi, F. & Fujiwara, T., 2009. Carbon dioxide stored and acidified low oxygen bottom waters in coastal seas, Japan. Estuarine, Coastal and Shelf Science in press (doi:10.1016/j.ecss.2009.07.037). Abstract (subscription required).