Distribution and Sea-to-air Flux of Nitrous Oxide in the East China Sea during the Summer of 2013

• N2O in the Changjiang (Yangtze River) Estuary and the East China Sea (ECS) were determined from August 4 to 31 of 2013.
• N2O emission from the ECS was estimated to be about (8.2-16.0)×10−2 Tg yr−1, suggesting that the ECS was a significant net source of atmospheric N2O.
• Frequent vertical mixing may enhance the emission of N2O from the hypoxic area.

Dissolved nitrous oxide (N2O) at different depths of 73 stations in the Changjiang (Yangtze River) Estuary and the East China Sea (ECS) were determined from August 4 to 31 of 2013, and the sea-to-air fluxes of N2O were also estimated in this study. N2O concentrations in the surface waters ranged from 6.33 to 44.40 nmol L−1 with an average of (9.27±4.30) nmol L−1 and the values in the bottom waters ranged from 5.19 to 26.98 nmol L−1 with an average of (11.87±3.71) nmol L−1. The concentrations of N2O decreased with distance from the Changjiang Estuary to the open sea. The vertical distributions of N2O indicated great spatial variations. A region of significant bottom-water hypoxia, with oxygen concentration less than 1.5 mg L−1, occurred at the north of the ECS, and increased bottom N2O concentrations was observed. Frequent vertical mixing may enhance the emission of N2O from this hypoxic area. N2O in the surface waters of all stations were over-saturated, and the N2O saturations ranged from 106% to 658%, with an average of (149±62)%. We estimated the sea-to-air fluxes of N2O as (30.6±59.1) μmol m−2 d−1 from the Changjiang Estuary, (9.8±8.8) μmol m−2 d−1 from the coastal and shelf, and (21.0±12.7) μmol m−2 d−1 from the continental slope using the Wanninkhof 1992 equation, (24.9±47.2) μmol m−2 d−1, (8.0±6.7) μmol m−2 d−1 and (16.5±9.6) μmol m−2 d−1 using the Nightingale 2000 equation, respectively. N2O emission from the ECS was estimated to be about (8.2-16.0)×10−2 Tg-N2O yr−1, suggesting that the ECS was a significant net source of atmospheric N2O.