Nitrous oxide (N₂O) is a strong greenhouse gas and an ozone depleting agent. In marine environments, N₂O is produced biologically via ammonium oxidation, nitrite, and nitrate reduction. The relative importance of these principle production pathways is strongly influenced by oxygen availability. We conducted ¹⁵N tracer experiments of N₂O production in parallel with measurements of N₂O concentration and natural abundance isotopes/isotopomers in Saanich Inlet, a seasonally anoxic fjord, to investigate how temporal and vertical oxygen gradients regulate N₂O production pathways and rates. In April, June, and August 2018, the depth of the oxic‐anoxic interface (dissolved oxygen = 2.5 μmol L⁻¹ isoline) progressively deepened from 110 to 160 m. Within the oxygenated and suboxic water column, N₂O supersaturation coincided with peak ammonium oxidation activity. Conditions in the anoxic deep water were potentially favorable to N₂O production from nitrate and nitrite reduction, but N₂O undersaturation was observed indicating that N₂O consumption exceeded rates of production. In October, tidal mixing introduced oxygenated water from outside the inlet, displacing the suboxic and anoxic deep water. This oxygenation event stimulated N₂O production from ammonium oxidation and increased water column N₂O supersaturation while inhibiting nitrate and nitrite reduction to N₂O. Results from ¹⁵N tracer incubation experiments and natural abundance isotopomer measurements both implicated ammonium oxidation as the dominant N₂O production pathway in Saanich Inlet, fueled by high ammonium fluxes (0.6–3.5 nmol m⁻² s⁻¹) from the anoxic depths. Partial denitrification contributed little to water column N₂O production because of low availability of nitrate and nitrite.

中文翻译：

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时间和垂直氧气梯度调节季节性缺氧峡湾中一氧化二氮的产生：不列颠哥伦比亚省Saanich入口

一氧化二氮（N ₂ O）是一种强温室气体，是一种臭氧消耗剂。在海洋环境中，N ₂ O是通过铵氧化，亚硝酸盐和硝酸盐还原而生物产生的。这些主要生产途径的相对重要性受到氧气供应的强烈影响。我们进行了^15次N ₂ O产生的示踪实验，并同时测量了季节性缺氧峡湾萨尼奇（Saanich）入口中的N ₂ O浓度和自然丰度同位素/同位素，以研究时间和垂直氧梯度如何调节N _2。O生产途径和速率。在2018年4月，6月和8月，含氧-缺氧界面的深度（溶解氧= 2.5μmolL ^-1等值线）从110 m逐渐加深到160 m。在含氧和低氧的水塔中，N ₂ O过饱和与铵氧化活性峰值同时发生。在缺氧深水条件潜在有利到N ₂从硝酸盐和亚硝酸盐还原ö生产，但Ñ ₂中观察到，表明N 2 O欠饱和₂ ö消耗超过生产的速率。十月份，潮汐混合从进口外部引入了氧化水，取代了低氧和缺氧的深水。该氧化事件刺激了N ₂从氧化铵ö生产和增加的水N列₂ ö过饱和，同时抑制硝酸盐和亚硝酸盐还原成N ₂从O.结果^15个Ñ示踪剂培养试验和天然丰度同位素测量都牵连铵氧化为主导Ñ ₂在萨尼奇ö生产途径进水口由缺氧深度的高铵通量（0.6–3.5 nmol m ^-2  s ^-1）提供燃料。由于硝酸盐和亚硝酸盐的利用率低，部分反硝化对水柱N ₂ O的生产几乎没有影响。