Abstract

Various parameterizations of gas exchange with wind speed at the ocean surface are poorly constrained by field measurements using natural and artificial tracers. One of the factors leading to uncertainty for in situ estimates of the gas transfer velocity is the presence of organic films at the air–sea interface. Such films are derived from bulk seawater dissolved organic matter, from terrestrial sources (natural and anthropogenic) and from petroleum seeps and spills. The ubiquitous background of degraded natural biopolymeric and geopolymeric materials in the sea potentially contributes to surface accumulations of organic matter even in very oligotrophic waters. Specific inputs during phytoplankton blooms and from neuston in the microlayer also contribute to the enrichment of surface-active matter at the interface.

Organic films can affect air–sea gas exchange through both static and dynamic mechanisms. The static effect arises from the presence of additional mass transfer resistance due to the physical barrier provided by the film. This effect is not considered to be important at the sea surface, since it requires the presence of condensed, solid type surfactant films that are easily dispersed under typical oceanic conditions of wind and waves. Much more significant is the hydrodynamic effect of a film that arises from the viscoelastic property of a surfactant-influenced interface.