High gas-transfer velocity in coastal regions with high energy-dissipation rates

We measured the gas-transfer velocity (k) and analyzed factors regulating k at coral reefs and an estuary at Ishigaki Island, Japan, using the floating- chamber method and the measured energy-dissipation rate (epsilon) to represent turbulence in a small-eddy model. We confirmed the validity of the floating- chamber method quantitatively for the first time by the comparing epsilon values inside and outside the chamber device. We also compared k to epsilon and empirical parameters such as wind and current speeds. Measured k had a low correlation with the empirical parameters and a high correlation with epsilon, as indicated by the small-eddy model. The high epsilon values may have been regulated by topographic conditions, e. g., corals or seagrasses that generate wakes, and complex coastlines or large-scale (on the order of kilometers) topographic factors that generate horizontal current shear. Our measurements indicate that coastal k is regulated by epsilon and cannot be accurately determined using wind or current speeds. Topographic conditions in coastal regions are important factors that regulate epsilon; thus, a quantitative analysis of the effects of these conditions is necessary to accurately determine coastal air-water gas flux.