Air-sea CO2 flux and gas exchange coefficient at the Sesoko coral reefs, Okinawa, Japan

The partial pressure of CO2 in seawater and air-sea CO2 flux were measured at the Sesoko coral reefs in Okinawa, Japan, and the effect of various perturbations on the gas exchange coefficient is discussed. The CO2 flux varied from -1.0 to 1.3mmol m-2h-1, which corresponded with the variation in partial pressure of CO2 in seawater. Atmospheric CO2 was absorbed by seawater during the day and released at night. This was mainly because of community photosynthesis and respiration. The gas exchange coefficient obtained from the chamber method was relatively larger than the wind dependent gas exchange coefficient. In the present study, the gas exchange coefficient was 5 and 30 times higher than that reported by Wanninkhof (1992) and Liss and Merlivat (1986), respectively when the wind velocity was set to 2.8m s-1. Our result (13.8±2.7cm h-1) was close to that reported by Komori and Shimada (1995), which took into account both the effects of turbulence and wind velocity on the gas exchange coefficient, indicating that not only wind, but also the effects of turbulence and other factors are important in the coefficient estimation at the Sesoko coral reefs.