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 (GHGs), nitrous oxide (N2O) is the third most impactful, possessing a global warming potential approximately 300 times greater than that of carbon dioxide (CO2) over a century. The distribution of N2O in aquatic environments exhibits notable spatial and temporal variations, and emissions remain inadequately constrained and underrepresented in global N2O emission inventories, particularly for coastal zones. This study focuses on N2O levels and air-sea fluxes in the coastal waters of the Balearic Islands Archipelago in the Western Mediterranean basin. Data were gathered between 2018 and 2023 at three coastal monitoring stations: two on the densely populated 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 nmolL-1, with no significant differences being detected across the sites. When these sink-source strengths are integrated on an annual basis, the Balearic Sea is close to equilibrium with atmospheric N2O, resulting in a neutral atmosphere-ocean exchange (0.1 ± 0.2 μmolm-2d-1). A consistent seasonal pattern was noted during 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.