- Institute of physical Chemistry, Kiel University, Kiel, Germany (schaefer@phc.uni-kiel.de)
The sea surface microlayer (SML) acts as a biogeochemical and (photo)chemical reactor. It is enriched with surfactants that modulate the physico-chemical properties of the interface. As such, the SML reduces the formation of capillary waves and thus turbulent air-sea gas exchange.
In recent years, the surface sensitive methods of Vibrational Sum Frequency Generation (VSFG) and Langmuir through compression isotherms (LT) have been used to characterize the state of the SML on the nanoscale. Here, we give a brief overview of the results obtained during the last decade, reporting on a variety of experiments ranging from (i) artificial laboratory experiments with model wet and dry surfactants (Triton X-100 and DPPC), (ii) semi-natural large-scale mesocosm experiments (SURF facility in Wilhelmshaven, Germany, 2023), and (iii) the analysis of natural samples. These include samples from a study targeting slick versus non-slick conditions (near Helgoland island, Germany, 2024), year-long time-series measurements at Boknis Eck Time series Station as well as during the Baltic GasEX campaign (Eckernförde Bay, Germany, 2009-2019). In this context, we have derived a surface coverage index as a proxy parameter to reduce the spectral VSFG information to a single parameter in order to enable correlation with other biogeochemical and physical variables, including surfactant activity based on AC voltammetry and wave damping data from previous studies.
We hypothesize that gas exchange reduction can be constrained by a surfactant coverage threshold. Working out solid correlation of biogeochemical parameters with surfactant coverage would help to better model the influence of the SML on large-scale air-sea gas exchange based on their climatologies.
How to cite: Schäfer, F., Lange, F.-D., Laß, K., and Friedrichs, G.: VSFG Based Surfactant Coverage Index - A Feasible Approach to Assess the Effect of the SML on Air-Sea Gas Exchange?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20597, https://doi.org/10.5194/egusphere-egu25-20597, 2025.