Old samples, new perspectives: Exploring nitrogen loss through nitrous oxide cycling in the Atlantic

海洋氮循环在海洋吸收和储存大气中二氧化碳的能力中起着重要作用。这是因为氮是海洋表层光合作用的关键营养物质。然而，在海洋内部，固定氮（可以用作营养物）转化为N2气体（不能）的方式尚不完全清楚。特别是，一氧化二氮（氮循环中的中间气体）是一种强效温室气体，它的产生和消耗有许多悬而未决的问题。本项目旨在通过测量约950个保存完好的溶解气体样本、现代水柱测量和船上孵育实验，更好地了解大西洋内部固定氮损失的动态。主要目标是绘制N2O分布及其同位素组成，量化固定N损失产生的过量N2，探索生物地球化学途径。该项目将包括学生（一名博士生和两名本科生）的实验室和实地机会。该项目还将通过仅消耗少量气体并使样本广泛供科学界成员使用，从而扩大这一大批溶解气体样本的覆盖范围。最后，从这项工作中产生的大型数据集将向公众提供，以支持本研究范围之外的其他项目。这项研究将填补大西洋内部关于N2O丰度和同位素组成的大量数据空白。有了这么大的一组样本，以同样的方式收集、储存和分析，就有了一个前所未有的机会来限制N2O及其同位素的空间变异性，而不需要实验室间校准的挑战，也不需要几十次巡航和多年的准备。同样，这项工作将建立在新的分析进展的基础上，这些进展允许测量N2/Ar比率和N2同位素作为自上而下的反硝化示踪剂。将20世纪80年代的储气罐与北大西洋深水地层（水团年龄小于40年）的现代测量结果进行比较，为探索近几十年来N循环的时间变化提供了一个独特的机会。船上孵化实验将为N2O循环提供新的机制见解，而N2O丰度和同位素组成的大型数据集将直接帮助同事们利用机器学习技术绘制全球海洋N2O变化图。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The marine nitrogen cycle plays a large role in the ocean’s ability to take up and store carbon dioxide from the atmosphere. This is because N is a key nutrient for photosynthesis in the surface ocean. However, the ways in which fixed N (which can be used as a nutrient) is converted to N2 gas (which cannot) in the ocean interior are not fully understood. In particular, there are many open questions about the production and consumption of N2O (an intermediate gas in the N cycle), a potent greenhouse gas. This project aims to better understand the dynamics of fixed N loss in the interior of the Atlantic Ocean through the measurement of ~950 well preserved dissolved gas samples, modern water column measurements, and shipboard incubation experiments. The major goals are to map the distribution of N2O and its isotopic composition, quantify excess N2 produced by fixed N loss, and explore biogeochemical pathways. The project will include lab and field opportunities for students (one PhD student and two undergraduate students). The project will also broaden the reach of this large set of dissolved gas samples by consuming only a small quantity of gas and making the samples widely available for members of the scientific community. Finally, the large data sets generated from this work will be made publicly available, supporting other projects beyond the scope of this study. This study will fill large data gaps in the Atlantic interior for the abundance and isotopic composition of N2O. With such a large set of samples that were collected, stored, and will be analyzed in the same way, there is an unprecedented opportunity to constrain the spatial variability of N2O and its isotopes without the challenges of inter-laboratory calibration, and without requiring dozens of cruises and years of preparation. Similarly, this work will build upon new analytical advances that permit the measurement of N2/Ar ratios and N2 isotopes as top-down tracers of denitrification. Comparison of stored gas tanks from the 1980s to modern measurements in North Atlantic regions of deep-water formation (where water mass ages are younger than 40 years) provides a unique opportunity to explore temporal changes in the N cycle over recent decades. Shipboard incubation experiments will provide new mechanistic insight into N2O cycling, and the large data set of N2O abundance and isotopic composition will directly aid in ongoing work by colleagues to employ machine learning techniques to map N2O variability in the global ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.