The sea surface microlayer (SML) is the thin layer on top of the ocean that is in direct contact with the atmosphere which is crucial for air–sea interactions. A novel paper shows data profiles close to the water surface in a mesocosm experiment. Using microsensor profiles at high vertical resolution, it shows dissolved oxygen and temperature gradients from the air, through the sea surface microlayer and into the water below. Phytoplankton bloom dynamics and surfactant concentrations influence the oxygen concentration and the diffusive layer depth but not temperature gradients. This has implications for air-sea exchanges across the sea surface microlayer.