Biogeochemical Shifts During Arctic Spring: Surfactants in the Sea-Surface Microlayer Reduce CH₄ and N₂O Emissions During the Onset of Sea Ice Melt

Abstract. The sea-surface microlayer (SML) is the less than one millimeter thin interface between the surface ocean and the overlying atmosphere and plays a crucial role in sea-air gas exchange processes. However, its role for sea-air exchange processes in sea ice-influenced environments such as the Arctic Ocean remains poorly understood. Here, we present the first in situ measurements of surfactants accumulating in the SML of the Fram Strait, coupled with near-surface measurements of the climate-relevant trace gases CH₄ and N₂O. Sampling of the undisturbed surface ocean was conducted at leads and ice holes during the onset of sea ice melt and an early algal bloom between May and June 2023. Our results reveal that the region acted as a minor source of CH₄ and N₂O. Nonetheless, the algal bloom stimulated the production of surfactants, which accumulated in the SML of open leads, reducing the emissions of CH₄ and N₂O to the atmosphere. These findings highlight the importance of resolving short-term surface processes during seasonal transitions and of integrating SML dynamics into investigating trace gas fluxes in polar regions.