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 (ɛ) 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 ɛ values inside and outside the chamber device. We also compared k to ɛ and empirical parameters such as wind and current speeds. Measured k had a low correlation with the empirical parameters and a high correlation with ɛ, as indicated by the small‐eddy model. The high ɛ 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 ɛ and cannot be accurately determined using wind or current speeds. Topographic conditions in coastal regions are important factors that regulate ɛ; thus, a quantitative analysis of the effects of these conditions is necessary to accurately determine coastal air–water gas flux.