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Subproject 1: Kinetics of film formation and the consequences for the diffusion of trace gases



Robert Schmidt, Jacek Beldowski, Bernd Schneider

The effect of organic surface films on the gas exchange transfer velocity (k) is investigated by laboratory experiments. A glass vessel with a volume of about 2 L was used to measure the air/water gas exchange of oxygen with an optode. Turbulence was generating by stirring of the water phase. Natural water samples from a coastal station were used and the surface tension was measured in order to characterize the film coverage that causes a decrease in the surface tension (Δσ) compared to organic-free seawater of the same salinity and temperature. It was shown that k decreases drastically by a factor of 2 – 3 already at low film coverages (Δσ < 0.5 mN/m), but that no further change occurred at higher film coverage (Fig. 1). A relationship between Δσ and biological production was so far not unambiguously identified but will be in the focus of future investigations.

Fig. 1: Transfer velocity k vs. deacrease of surface tension Δσ