Distributions and fluxes of dissolved nitrous oxide in the Bohai Sea in autumn and winter and their influencing factors

Distributions and air-sea fluxes of dissolved N₂O in the Bohai Sea were investigated in October and December 2019. Dissolved N₂O concentrations in surface waters were (8.2±0.5) nmol/L (97.5%±4.7)% saturation in autumn and (11.0±0.8) nmol/L (93.8±4.5)% saturation in winter. Generally, surface N₂O concentrations in winter were higher than in autumn. High N₂O concentrations were observed mainly near the Yellow River Estuary and Laizhou bay. N₂O in the Bohai Sea was close to saturation in autumn and undersaturated in winter. Temperature, riverine input and sediment-water exchange are major factors affecting distributions of dissolved N₂O in the Bohai Sea. The freshwater input from the Yellow River was an important source of N₂O in the Bohai Sea, with fluxes of about 4.2×10⁴ mol in October 2019 and 1.1×10⁴ mol in December 2019. Sediment can act as either a source or a sink of water column N₂O in autumn and winter. The air-sea fluxes of the Bohai Sea were about (−0.3±0.7) μmol/(m²∙d) in autumn and (−1.1±1.6) μmol/(m²∙d) in winter, and were lower than from other coastal seas of China. The Bohai Sea acted as a N₂O sink of the atmosphere in autumn and winter with a total influx of 4.41×10⁻⁴ Tg.