Spatio-temporal heterogeneity in marine nitrous oxide emissions of the South Pacific

Nitrous oxide (N₂O) is a powerful greenhouse gas and ozone depleting substance, but its natural sources, especially marine emissions, are poorly constrained. Localized high concentrations have been observed in the oxygen minimum zones (OMZs) of the tropical Pacific but the impacts of El Niño cycles on this key source region are unknown. Measurements from an atmospheric monitoring station in Samoa combined with atmospheric back-trajectories provide novel information on N₂O emissions across the southern Pacific basin. Remarkable elevations in Samoan concentrations are obtained in air parcels that pass over the OMZ compared to the bulk Pacific. The data further reveal that average concentrations over the OMZ are augmented during La Niña but crash during El Niño. These natural spatial heterogeneities and temporal dynamics in marine emissions can confound attempts to interpret observed N₂O variability and quantify anthropogenic feedbacks on this climatically active gas as low oxygen zones are predicted to expand and El Niño cycles change.