For studying the biological composition of the microlayer as well as to explore gas-exchange processes at the air sea interface under tightly controlled conditions, we took part in an interdisciplinary project at the Aeolotron in Heidelberg. The Aeolotron is an annular wind-wave system which allows simulation of wave movements by controlling wind speeds. The water for flooding the channel (20000 liters indeed) originated from the North Atlantic and has been shipped to Heidelberg with a truck.
We used a glass plate to sample the surface microlayer (SML) at different wind speeds. For this purpose, the plate gets submerged in water perpendicular to the water surface. The microlayer then adheres to the glass surface and can be scraped off into a container. For comparing SML- with bulk water properties, a bulk water sample has also been taken for each wind condition.
We know the SML to contain a range of organic molecules such as carbohydrates, proteins and fatty acids. Thereby it forms a unique environment for bacteria and other microbes that can metabolize those substances. We therefore measured surfactant concentration and surface tension of the layer under the influences of different wind forces.
Since we are mainly interested in studying CO2 fluxes through the SML, we measured pCO2 in air and water. We will then calculate the gas transfer velocity and fluxes and try to related with SML composition. For investigation of bacterial communities within the SML we took 0.22µm-filtered bulk and SML water samples as well as fixed water samples to the home laboratory. Molecular analysis and flow cytometry will help us to understand the microbial role in the microlayer. Experiments and analysis are still in progress.
A film about the work at Aeolotron can be found here