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

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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.

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