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 ∼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.