Drivers of the spatiotemporal distribution of dissolved nitrous oxide and air-sea exchange in a coastal Mediterranean area

Abstract. Among the well-known greenhouse gases (GHG), nitrous oxide (N₂O) is the third most impactful, possessing a global warming potential approximately 300 times greater than carbon dioxide (CO₂) over a century. The distribution of N₂O from aquatic environments exhibits notable spatial and temporal variations, and emissions still remain inadequately constrained and underrepresented in global N₂O emission inventories, particularly from coastal zones. This study focuses on the N₂O levels and air-sea fluxes in the Balearic Islands Archipelago coastal waters in the Western Mediterranean Basin. Data were gathered between 2018 and 2023 at three coastal monitoring stations: two in the highly inhabited island of Mallorca and the third in the well-preserved National Park of the Cabrera Archipelago. Seawater N₂O concentrations varied from 6.5 to 9.9 nM, with no significant differences detected across the sites. The average air-sea fluxes were estimated to range from -0.3 to 0.6 μmol m⁻² d⁻¹, indicating that the study areas generally functioned as weak N₂O sources. A consistent seasonal pattern was noted over the study period. Machine learning analysis indicated that seawater temperature was the primary factor influencing N₂O concentrations, with lesser contributions from chlorophyll levels and salinity.