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Distribution and Production of N2O in the Subtropical Western North Pacific Ocean During the Spring of 2020

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Heo, JM 
Kim, HR 
Eom, SM 
Yoon, JE 
Shim, JH 


jats:pNitrous oxide (Njats:sub2</jats:sub>O) is an important greenhouse gas emitted in significant volumes by the Pacific Ocean. However, the relationship between Njats:sub2</jats:sub>O dynamics and environmental drivers in the subtropical western North Pacific Ocean (STWNPO) remains poorly understood. We investigated the distribution of Njats:sub2</jats:sub>O and its production as well as the related mechanisms at the surface (0–200 m), intermediate (200–1500 m), and deep (1500–5774 m) layers of the STWNPO, which were divided according to the distribution of water masses. We applied the transit time distribution (TTD) method to determine the ventilation times, and to estimate the Njats:sub2</jats:sub>O equilibrium concentration of water parcels last in contact with the atmosphere prior to being ventilated. In the surface layer, biologically derived Njats:sub2</jats:sub>O (ΔNjats:sub2</jats:sub>O) was positively correlated with the apparent oxygen utilization (AOU) (Rjats:sup2</jats:sup> = 0.48), suggesting that surface Njats:sub2</jats:sub>O may be produced by nitrification. In the intermediate layer, ΔNjats:sub2</jats:sub>O was positively correlated with AOU and jats:inline-formula<mml:math xmlns:mml="" display="inline" id="im1">mml:mrowmml:msubsupmml:mrowmml:mtextNO</mml:mtext></mml:mrow>mml:mn3</mml:mn>mml:mo−</mml:mo></mml:msubsup></mml:mrow></mml:math></jats:inline-formula> (Rjats:sup2</jats:sup> = 0.92 and Rjats:sup2</jats:sup> = 0.91, respectively) and negatively correlated with nitrogen sinks (Njats:sup*</jats:sup>) (Rjats:sup2</jats:sup> = 0.60). Hence, the highest ΔNjats:sub2</jats:sub>O value in the oxygen minimum layer suggested Njats:sub2</jats:sub>O production through nitrification and potential denitrification (up to 51% and 25% of measured Njats:sub2</jats:sub>O, respectively). In contrast, the deep layer exhibited a positive correlation between ΔNjats:sub2</jats:sub>O and AOU (Rjats:sup2</jats:sup> = 0.92), suggesting that the Njats:sub2</jats:sub>O accumulation in this layer may be caused by nitrification. Our results demonstrate that the STWNPO serves as an apparent source of atmospheric Njats:sub2</jats:sub>O (mean air−sea flux 2.0 ± 0.3 μmol mjats:sup-2</jats:sup> djats:sup-1</jats:sup>), and that nitrification and potential denitrification may be the primary mechanisms of Njats:sub2</jats:sub>O production in the STWNPO. We predict that ongoing ocean warming, deoxygenation, acidification, and anthropogenic nitrogen deposition in the STWNPO may elevate Njats:sub2</jats:sub>O emissions in the future. Therefore, the results obtained here are important for elucidating the relationships between Njats:sub2</jats:sub>O dynamics and environmental changes in the STWNPO and the global ocean.</jats:p>



nitrous oxide, greenhouse gas, North Pacific Ocean, oxygen minimum layer, air-sea gas exchange, climate change

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Frontiers in Marine Science

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Frontiers Media SA