Nitrous oxide (N₂O), a potent greenhouse gas, is produced disproportionately in marine oxygen deficient zones (ODZs). To quantify spatiotemporal variation in N₂O cycling in an ODZ, we analyzed N₂O concentration and isotopologues along a transect through the eastern tropical North Pacific (ETNP). At several stations along this transect, N₂O concentrations reached a near surface maximum that exceeded prior measurements in this region, of up to 226.1 ± 20.5 nM at the coast. Above the σ_θ = 25.0 kg/m³ isopycnal, Keeling plot analysis revealed two sources to the near‐surface N₂O maximum, with different δ¹⁵N₂O^α and δ¹⁵N₂O^β values, but each with a site preference (SP) of 6‰–8‰. Given expected SPs for nitrification and denitrification, each of these sources could be comprised of 17%–26% nitrification (bacterial or archeal), and 74%–83% denitrification (or nitrifier‐denitrification). Below the σ_θ = 25.0 kg/m³ isopycnal, box model analysis indicated that the observed 46‰–50‰ SPs in the anoxic core of the ODZ cannot be reproduced in a steady state context without an SP for N₂O production by denitrification, and may indicate instead a transient net consumption of N₂O. Furthermore, time‐dependent model results indicated that while δ¹⁵N₂O^α and δ¹⁸O‐N₂O reflect both N₂O production and consumption in the anoxic core of the ODZ, δ¹⁵N₂O^β predominantly reflects N₂O sources. Finally, we infer that the high (N₂O) observed at some stations derive from a set of conditions supporting high rates of N₂O production that have not been previously encountered in this region.

中文翻译：

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用同位素异构体分析法量化北太平洋东部热带地区的一氧化二氮循环形式

一氧化二氮（N ₂ O）是一种有力的温室气体，在海洋缺氧区（ODZs）中成比例地产生。为了量化ODZ中N ₂ O循环中的时空变化，我们分析了穿过东部热带北太平洋（ETNP）的样带的N ₂ O浓度和同位素。在该断面的几个站点上，N ₂ O的浓度达到了近地表最大值，超过了该区域以前的测量值，在海岸处达到226.1±20.5 nM。上面的σ _θ  =25.0公斤/米³等密度，Keeling曲线分析揭示了两个源到近面N ₂ O最大，具有不同的δ ¹⁵ Ñ ₂Ò ^α和δ ¹⁵ Ñ ₂ ö ^β值，但每个具有6‰的位点优先（SP）-8‰。给定硝化和反硝化的预期SP，这些来源中的每一个可能包括17％–26％的硝化作用（细菌或古细菌）和74％–83％的反硝化作用（或硝化剂-反硝化作用）。下面的σ _θ  =25.0公斤/米³等密度，盒模型分析表明，在ODZ不能在稳定状态下的上下文被再现的缺氧核心观察到46‰-50‰的SP没有SP对于N ₂通过反硝化ö生产，而可能表示N ₂的瞬时净消耗O.此外，依赖于时间的模型的结果表明，虽然δ ¹⁵ Ñ ₂ ö ^α和δ ¹⁸ O-N ₂ ö反映均为N ₂ ö生产和消费的ODZ的缺氧核心，δ ¹⁵ Ñ ₂ ö ^β主要反映N ₂ O源。最后，我们推断在某些站点观测到的高（N ₂ O）来自一组条件，该条件支持该区域以前未遇到的高N ₂ O产生速率。