Summer N₂O dynamics in the western Arctic Ocean : Distributions, Processes, and Fluxes

We collect seawater samples from 32 stations for N₂O analysis between August 6 and August 25, during 2017 ARA08B cruise in western Arctic Ocean (WAO), covering from Southern Chukchi Sea (SC) to Northern Chukchi Sea (NC). At surface depth (~50 m), N₂O concentrations were 10.9‒19.4 nmol L^-1, and distinct pattern was observed between SC and NC. N₂O concentrations were increased from surface to bottom (~50 m) at SC, corresponding to positive relationship of ∆N₂O (N₂O_measured - N₂O_equilibrium) with DIN (NO_3­^- + NO₂^-) and negative relationship between ∆N₂O and N^*. It suggests that nitrification and denitrification are the main processes to produce N₂O at SC. On the other hand, N₂O concentration at NC increased from the south to north, and remained vertically constant. It may be the result of physical processes such as dilution by sea ice melting water, and high solubility that affected by low temperature and low salinity. The highest N₂O concentrations were observed at intermediate depth (50‒200 m), ranging 13.4‒21.9 nmol L^-1. It would be determined by high solubility and active biogeochemical processes synthetically. Concentrations of N₂O were rapidly diminished to 400 m, ranging 10.2‒14.1 nmol L^-1, and did not be remarkably altered under 400 m, ranging 11.3‒13.7 nmol L^-1. It might be affected by advection of Atlantic Water (AW) and existence of Arctic Bottom Water (ABW), and influence of biogeochemical processes was negligible at deep and bottom depth (below 200 m). N₂O flux was calculated to determine that the WAO is sources or sinks region for atmospheric N₂O. Positive N₂O flux was observed at SC, and it indicate that N₂O gas is released to atmosphere at SC. Negative value of N₂O flux at NC suggest that atmospheric N₂O is absorbed into NC. Furthermore, positive relationship of N₂O flux with environmental parameters (temperature, salinity, and ∆N₂O) also observed in WAO. These results provide comprehensive information of the spatial N₂O distribution and main processes which decide N₂O distribution in WAO, and also suggest that air-sea N₂O flux could be affected by changing environments of the Arctic Ocean.