Continuous observations of atmospheric and oceanic CO2 using a moored buoy in the East China Sea: Variations during the passage of typhoons

An automatic measuring system for the partial pressure, pCO2, of atmospheric and oceanic carbon dioxide was developed. The system was mounted on a moored buoy for routine observation of maritime meteorology in the East China Sea. CO2 observations were conducted from June 29, 1997 to January 6, 1998. During the observation period, the atmospheric pCO2 showed little variation (341–365 μatm), whereas pCO2 in the surface water varied significantly (308–408 μatm). In the summer, pCO2 was higher in the surface water than in the overlying atmosphere, implying that this area was a source for atmospheric CO2, though it became a sink after late September. Time-series data clearly exhibited significant short-term variations in the oceanic pCO2, i.e. sudden variations during the passage of typhoons, and diurnal variations driven by the diurnal variations in the sea-surface temperature under calm conditions. The effects of typhoons on ocean–atmosphere CO2 exchange at the surface could differ, depending on the relative position of the mooring site with respect to the center of the moving typhoons. These differences result from the different contributions of sea-surface cooling, entrainment, and upwelling. The efflux enhanced by three typhoons accounted for 60% of the efflux of CO2 in the warm season. It is suggested that typhoons have a significant impact on the carbon cycle in the western subtropical North Pacific.