Air-Sea Gas Exchange in Marine Surface Microlayers

The sea surface microlayer (SML) is the ultra-thin boundary—typically less than one millimetre thick—between ocean and atmosphere, distinguished by elevated concentrations of organic films, microbial communities and surface-active compounds. This interfacial habitat mediates the transfer of key gases such as carbon dioxide, oxygen and trace climate-active compounds via a combination of physical damping of small-scale turbulence and biochemical modification of surface rheology. Factors including wind speed, biological productivity and regional oceanography govern the patchy distribution and temporal dynamics of the SML, which in turn influence global biogeochemical cycles, marine aerosol production and the accuracy of climate models.

Research from Nature Portfolio

Recent work has shown that specialised marine bacteria synthesise amphiphilic compounds that accumulate in the near-surface layer and form natural slicks visible in radar imagery. Molecular analyses revealed that these surfactant-associated taxa are most abundant beneath slicks and actively mediate the transport of organic films to the air–sea interface. By producing and degrading surface-active molecules, these bacterial communities alter surface tension and film properties, with direct implications for the rates of gas exchange and the emission of climate-relevant aerosols under varying physical conditions.

Air-Sea Gas Exchange in Marine Surface Microlayers publication trend

The graph below shows the total number of articles in air-sea gas exchange in marine surface microlayers across all publications each year (not limited to Nature Index journals).

Technical terms

Synthetic aperture radar (SAR): A satellite-based radar technique producing high-resolution images of the sea surface by utilising the motion of the radar platform.

Sea surface microlayer (SML): The topmost 1–1000 µm of the ocean surface, enriched in organic matter, microbes and surfactants.

Surfactant: An amphiphilic organic molecule that accumulates at the air–water interface, reducing surface tension and altering gas exchange rates.

Gas transfer velocity (kw): A parameter expressing the rate at which gases cross the air–sea interface, influenced by surface films and small-scale turbulence.

References

1. Sea surface microlayer in a changing ocean – A perspective. Elementa: Science of the Anthropocene (2017).
2. Biological modification of mechanical properties of the sea surface microlayer, influencing waves, ripples, foam and air-sea fluxes. Elementa: Science of the Anthropocene (2018).
3. Monitoring the Sea Surface Microlayer (SML) on Sentinel images. The Science of The Total Environment (2023).
4. Surfactant-associated bacteria in the near-surface layer of the ocean. Scientific Reports (2016).
5. Surfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tank. Biogeosciences (2016).
6. Selective Ocean–Atmosphere Bacterial Flux Through the Pacific Sea Surface Microlayer. ACS ES&T Air (2025).