Studies of air-sea gas transfer and micro turbulence at the ocean surface using passive thermography

Abstract

Knowledge about the mechanisms of mass transfer across the aqueous boundary layer is still marginal because of the lack of suitable experimental techniques. We present a new technique to measure the air-water gas transfer rate and the spatial structure of the micro turbulence at the ocean surface using passive thermography. We make use of the fact that due to radiative cooling, latent and sensible heat fluxes across the interface, the ocean surface is generally a few tenths of a degree colder than the water bulk (‘cool skin of the ocean’). Therefore sea surface temperature fluctuations asso- ciated with the interplay of diffusive and turbulent transfer at the air/sea interface give a direct insight into the transport mechanisms. We modeled the relation between statistical properties of the temperature fluctuations and the mean temperature dif- ference across the aqueous thermal boundary layer. Furthermore, a first study of the spatial structure of the micro turbulence by means of digital image sequence analysis is presented.