Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3-D Inverse Model
Assessing Marine Nitrogen Cycle Rates and Process Sensitivities With a Global 3-D Inverse Model
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DOI：
10.1029/2018gb006088
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发表时间：
2019-08-01
影响因子：
5.2
通讯作者：
Casciotti, K. L.
中科院分区：
文献类型：
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作者：
Martin, T. S.;Primeau, F.;Casciotti, K. L.
我们提出了一个全球海洋氮（N）循环模型，包括硝酸盐（NO3-）和亚硝酸盐（NO2-）的浓度和它们的N同位素组成的限制在海洋缺氧区（ODZs）的N循环过程速率的结果。NO2-是氮循环中的重要中间体，特别是在臭氧消耗区中，它是氮损失过程、反硝化和厌氧氨氧化的基质。类似于早期的工作，我们的模型产生的总水柱N损失率为61 - 10 Tg N/年。然而，通过包括NO2-及其N同位素组成，我们能够评估反硝化和厌氧氨氧化氮损失的相对贡献，并检查一些潜在的驱动程序的平衡。我们发现，厌氧氨氧化贡献了全球水柱氮损失的60%，占主导地位的氮损失沿着边缘的ODZ，而反硝化作用是更重要的缺氧ODZ核心。厌氧氨氧化和反硝化的解耦是由NO2-氧化支持的，NO3-还原和厌氧氨氧化共同发生在ODZ中。高速率的NO2-氧化（高达400纳米/天），这是紧密耦合到异养NO3-还原，需要匹配NO3-和NO2-浓度和同位素观测海洋臭氧消耗区。通过调整O-2敏感参数降低ODZs中NO2-氧化的速率导致更高的水柱N损失速率，突出NO2-氧化在维持海洋固定N inventory.Plain Language摘要中的作用我们创建了一个全球氮（N）循环模型来研究海洋缺氧区（ODZs）中不同形式的N之间的转化。在这些地区，氧气浓度非常低，微生物过程从海洋中去除生物可利用的N。了解氮的损失是很重要的，因为低氮可用性可以限制海洋表层的碳吸收。以前的研究表明，一个需要氧气的过程，亚硝酸盐氧化，可能有助于防止氮的损失和周围的臭氧消耗区。使用我们的模型，它准确地模拟了海洋和臭氧破坏区中的氮浓度和同位素，我们已经表明，亚硝酸盐氧化确实是必要的臭氧破坏区，以使模型结果与现有的测量结果相匹配。从臭氧消耗区去除亚硝酸盐氧化导致氮损失率过高，浓度和同位素分布与观测结果不匹配。
We present results from a global inverse marine nitrogen (N) cycle model that include nitrate (NO3-) and nitrite (NO2-) concentrations and their N isotopic compositions as constraints on N cycle process rates in marine oxygen deficient zones (ODZs). NO2- is an important intermediate in the N cycle, particularly in ODZs where it is a substrate in the N loss processes, denitrification, and anammox. Similar to earlier work, our model yields a total water column N loss rate of 61 10 Tg N/year. However, by including NO2- and its N isotopic composition, we are able to assess the relative contributions of denitrification and anammox to N loss and examine some of the potential drivers of that balance. We find that anammox contributes 60% of global water column N loss, dominating N loss along the edges of ODZs, while denitrification is more important in the anoxic ODZ cores. The decoupling of anammox and denitrification is supported by NO2- oxidation, which co-occurs with NO3- reduction and anammox in ODZs. High rates of NO2- oxidation (up to 400 nM/day), which are tightly coupled to heterotrophic NO3- reduction, are required to match NO3- and NO2- concentration and isotope observations in marine ODZs. Lowering the rate of NO2- oxidation in ODZs by adjusting O-2-sensitive parameters results in higher rates of water column N loss, highlighting the role of NO2- oxidation in maintaining the marine fixed N inventory.Plain Language Summary We have created a global nitrogen (N) cycle model to study the transformations between different forms of N in marine oxygen deficient zones (ODZs). In these regions, oxygen concentrations are very low and microbial processes remove bioavailable N from the ocean. Understanding N loss is important because low N availability can limit carbon uptake in the surface ocean. Previous research has implied that an oxygen-requiring process, nitrite oxidation, may help prevent N loss in and around ODZs. Using our model, which accurately models the N concentrations and isotopes in the ocean and in ODZs, we have shown that nitrite oxidation is indeed necessary in ODZs in order for the model results to match existing measurements. Removing nitrite oxidation from ODZs results in rates of N loss that are too high and concentration and isotope profiles that do not match observations.