Using Phytoplankton Cultures as a Guide to Replicate the Sea-Surface Microlayer for Laboratory Experiments

The sea surface microlayer (SSML) is a chemically unique environment present at the air/water interface, caused by the concentration of insoluble or semi-soluble materials at the water surface. SSML composition in the environment is complex and variable, making it difficult to study in the laboratory. Studies investigating the composition of the SSML in the environment have identified classes of molecules that are derived from biological processes, such as carbohydrates, lipids, and amino acids. Investigating the chemical reactions that occur through photochemistry and/or heterogeneous oxidation are difficult to pinpoint within such chemical complexity. Studies have simplified the SSML to study the system by selecting a few model compounds, and recently a few studies have used phytoplankton cultures to generate a model SSML. We use axenic cultures of Thalassiosira pseudonana, a common diatom, to reproduce the natural SSML. We determine the approximate SSML composition using techniques commonly used in the field, to compare the axenic T. pseudonana culture composition to measured natural SSML composition. We compared carbohydrate, transparent exopolymer particles (TEP), and lipid concentration within the axenic phytoplankton cultures and compare them to field measurements to show that phytoplankton cultures are an appropriate model SSML.