Tidal influence on the sea-to-air transfer of CH4 in the coastal ocean

We obtained real-time monitoring data of water temperature, salinity, wind, current, CH4 and other oceanographic parameters in a coastal bay in the southern sea of Korea from July 8 to August 15, 2003, using an environmental monitoring buoy. In general, the transfer velocity of environmental gases across the air–sea interface is obtained exclusively from empirical relationships with wind speeds. However, our monitoring data demonstrate that the agitation of the aqueous boundary layer is controlled significantly by tidal turbulence, similar to the control exercised by wind stress in the coastal ocean. The sea-to-air transfer of CH4 is enhanced significantly during spring tide due to an increase in the gas transfer velocity and vertical CH4 transport from bottom water to the surface layer. Thus, our unique timeseries results imply that the sea-to-air transfer of gases, such as CH4, DMS, DMHg, N2O, CO2 and 222Rn, from highly enriched coastal bottom waters, is controlled not only by episodic wind events but also by regular tidal turbulence in the coastal ocean.