Nitrous oxide and methane concentrations and air-sea fluxes in undersampled areas of the Mediterranean basin

Abstract. Nitrous oxide (N₂O) and methane (CH₄) are potent greenhouse gases for which oceanic contributions remain uncertain, particularly in undersampled regions like the Southwest and Southeast margins of the Mediterranean Sea, where there is a major observational gap. This data paper presents a comprehensive dataset of monthly N₂O and CH₄ concentrations and air-sea fluxes collected over a full seasonal cycle (April 2023 – June 2024 at most sites, with one station extended to September 2024) from eight coastal stations across three distinct Mediterranean ecoregions (Alboran, Balearic, and Levantine Seas) as part of the ROADSTER collaborative project. Sampling, preservation, and analytical procedures were standardized across sites, and dissolved-gas analyses were performed in a single laboratory to ensure comparability. We detail standardized sampling and analytical methodologies, including ancillary variables (temperature, salinity, dissolved oxygen, chlorophyll a and inorganic nutrients). The complied dataset reveals distinct seasonal and spatial variability: N₂O concentrations exhibit a strong negative correlation with temperature, with all stations acting as moderate N₂O sources. Conversely, CH₄ concentrations show greater variability and a positive correlation with temperature, with the Levantine sub-basin stations displaying episodic high-flux events (up to 35.20 μmol m⁻² d⁻¹) indicative of localized seafloor sources. This dataset bridges significant data gaps in the Mediterranean, providing a crucial baseline for regional climate modeling, understanding biogeochemical processes, and future climate change impact assessments.