Photo‐Reactivity of Surfactants in the Sea‐Surface Microlayer and Subsurface Water of the Tyne Estuary, UK

We report the first estimates of total surfactant photo-reactivity in the sea-surface microlayer (SML) and in subsurface water (SSW) (Tyne estuary, UK; salinity 0.3-32.0). In addition to temperature, a known driver of surfactant adsorption kinetics, we show that irradiation contributes independently to enhanced interfacial surfactant activity (SA), a notion supported by coincident CDOM photodegradation. We estimate a mean SA production via irradiation of 0.064 +/- 0.062 mg l(-1) T-X-100 equivalents h(-1) in the SML and 0.031 +/- 0.025 mg l(-1) T-X-100 equivalents h(-1) in the SSW. Using these data, we derive first-order estimates of the potential suppression of the gas transfer velocity (k(w)) by photo-derived surfactants similar to 12.9%-22.2% in coastal North Sea water. Given the ubiquitous distribution of natural surfactants in the oceans, we contend that surfactant photochemistry could be a hitherto unrecognized additional driver of air-sea gas exchange, with potential implications for global trace gas budgets and climate models.