Distributions and sea-to-air fluxes of nitrous oxide in the South China Sea and the West Philippines Sea

• The surface N2O concentration were 7.59±1.32 nmol L−1 and 5.19±1.26 nmol L−1 in the SCS and the WPS, respectively.
• The calculated sea-to-air flux were 5.5±3.9 µmol m−2 d−1 in the SCS and −1.7±3.9 µmol m−2 d−1 in the WPS.
• The SCS emitted 19.3×106 mol d−1 N2O to the atmosphere and exported 8.5×106 mol d−1 N2O to the WPS during the wet season.

Approximately 600 water samples from the South China Sea (SCS) and 250 water samples from the West Philippines Sea (WPS) were collected during seven cruises from August 2003 to July 2007 to determine nitrous oxide (N2O) distributions between the surface and a maximum depth of 4250 m. In the SCS, the average surface N2O concentration exceeded the atmospheric equilibrium concentration (on average 132±23%); however in the WPS, the surface N2O concentration was lower than the atmospheric equilibrium concentration (on average 90±22%). The N2O concentration reached a maximum (~23 nmol L−1) in the WPS at 800–1000 m, and (~28 nmol L−1) at a shallower depth of around 600–800 m in the SCS, owing to vertical mixing and intensive upwelling in the SCS. In the SCS, the surface N2O concentration was 7.59±1.32 nmol L−1 and the calculated sea-to-air flux was 5.5±3.9 μmol m−2 d−1. The surface N2O concentration in the WPS, 5.19±1.26 nmol L−1, was lower than that in the SCS. The WPS is a sink for N2O and the calculated sea-to-air flux was −1.7±3.9  μmol m−2 d−1. The SCS emitted 19.3×106 mol d−1 N2O to the atmosphere and exported 8.5×106 mol d−1 N2O to the WPS during the wet season.