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发挥着重要作用。这是因为氮是海洋表层光合作用的关键营养素。然而，在海洋内部，固定氮（可用作营养物）转化为N2气体（不能）的方式尚未完全了解。特别是，有许多关于N2 O（氮循环中的中间气体）的生产和消费的问题，这是一种强大的温室气体。该项目旨在通过测量~950个保存完好的溶解气体样品、现代水柱测量和船上培养实验，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N2 O及其同位素组成的分布图，量化固定N损失产生的过量N2，并探索非地球化学途径。该项目将包括实验室和现场的机会，为学生（一名博士生和两名本科生）。该项目还将通过仅消耗少量气体并向科学界成员广泛提供样本来扩大这一大型溶解气体样本集的覆盖范围。最后，这项工作产生的大型数据集将公开提供，支持本研究范围以外的其他项目。这项研究将填补大西洋内陆N2 O丰度和同位素组成的大量数据空白。有了如此大量的样本，这些样本被收集、储存并将以相同的方式进行分析，就有了一个前所未有的机会来限制N2 O及其同位素的空间变异性，而不需要实验室间校准的挑战，也不需要数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，允许测量N2/Ar比和N2同位素作为自上而下的反硝化示踪剂。从20世纪80年代到现代测量在北大西洋地区的深水形成（水团年龄小于40年）存储的气罐的比较提供了一个独特的机会，探索在最近几十年的N循环的时间变化。船上培养实验将为N2 O循环提供新的机理见解，N2 O丰度和同位素组成的大数据集将直接帮助同事们正在进行的工作，利用机器学习技术绘制全球海洋中N2 O的变化。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查进行评估来支持的搜索.

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.