Abstract: The acquisition of seawater carbonate system parameters is essential to understand the carbon cycle in coastal ocean, the pattern of CO2 sources and sinks and assess the potential of carbon sinks. Based on the data obtained by 4 seasonal cruises conducted off Changjiang (Yangtze River) Estuary and adjacent East China Sea in March, July, November and December in 2011, we discuss the seasonal and spatial distributions of dissolved inorganic carbon (DIC) and total alkalinity (TA) and their influencing factors. The results showed that the averaged DIC and TA concentrations in inner shelf were increased from summer to autumn, then winter to spring; In cross-section distribution, DIC and TA in summer and autumn showed stratification pattern due to the influence of Changjiang Diluted Water, while in spring and winter, DIC and TA were vertically uniform due to mixing. In inner East China Sea shelf, transect DIC showed a significant negative correlation with temperature and dissolved oxygen, while TA was less regulated by temperature and dissolved oxygen changes, but positively correlated with salinity. DIC was significantly positively correlated with apparent oxygen consumption (AOU), while pH was significantly negatively correlated with AOU. The slope of pH/AOU in the outer East China Sea shelf was -0.002 7 pH/(μmol·kg-1), which was much higher compared with that of -0.001 8 pH/(μmol·kg-1) in the inner shelf. The inner East China Sea shelf seawater (water depth is less than 200 meters) was affected by seasonal ventilation and had stronger carbonate system buffer capacity, which alleviated the seasonal acidification in the subsurface water induced by organic matter decomposition.

Key words:  seawater carbonate system, seasonal characteristic, Changjiang (Yangtze River) Estuary, East China Sea； Kuroshio Subsurface Water (KSSW), ocean acidification