School of Natural and Environmental Sciences


Influence of offshore-onshore surfactant gradients on air-sea gas exchange

Climate models require detailed knowledge of the air-sea gas exchange process. Although advances have been made in recent years, a robust quantification of the air-sea gas transfer velocity kw (the parameter which determines the gas exchange rate together with the concentration difference of the respective substance and which is controlled by environmental parameters like wind, waves, surface films) remains elusive and it is now commonly accepted that besides wind speed, additional parameters have to be considered.

The key hypothesis of this project is that natural surfactants and its onshore-offshore gradients significantly influence air-sea gas exchange. A robust relation between surfactant activity and the transfer velocity kw will be established over a wide parameter range through laboratory experiments with in-situ samples. A time series of surface seawater samples and microlayer surfactants will be collected along the Tyne estuary and offshore into the North Sea. These will be used in laboratory gas exchange experiments in Newcastle and Heidelberg (within a collaboration with the gas exchange group at the IUP) to directly quantify the influence of surfactant activity on kw.

Newcastle-based experiments will be carried out in a closed tank with baffle-driven turbulence. Due to the absence of wind generated turbulence these experiment are particularly suitable for the extraction of detailed process information. The Heidelberg experiments, on the other hand, will use a tank with turbulence produced by generated winds, more representative of the natural situation. Surfactant activity (concentration) will be estimated with AC voltammetry and 3-D fluorescence excitation-emission spectra will provide some broad compositional data.