Collaborative Research: Deciphering the mechanisms of marine nitrous oxide cycling using stable isotopes, molecular markers and in situ rates

一氧化二氮（N2O）是一种强大的温室气体，也是平流层臭氧消耗的驱动因素。海洋低氧区对N2O循环非常重要，是大气中N2O的主要来源。印度洋西北部的阿拉伯海拥有世界上最大的低氧区之一，但它比其他地区研究得更少。该团队将与美国和印度的其他研究人员合作，将联合收割机地球化学和微生物生态学方法结合起来，研究阿拉伯海的N2O循环。该项目将支持一名博士后研究员和两名研究生。一些本科生将参加实验室和海上。一名来自位于印度喀拉拉邦科钦科技大学（科钦科技大学）的硕士学生也将被邀请参加至少一次研究航行，并参加南卡罗来纳州大学海洋稳定同位素生物地球化学实验室为期6周的实习。美国博士后和研究生将参加为期10天的印度早期职业研究人员地球化学区域培训计划。项目小组将从海上进行公众宣传。他们还将制作一个关于低氧区氮循环的免费电子讲座。该项目将通过使用天然丰度稳定同位素和同位素异构体数据、15 N标记孵育物、以及基因组学和元转录组学方法。实地工作计划于2024年和2025年夏季进行。第一次实地活动将是在由海军研究办公室（ONR）资助的机会巡航期间，作为阿拉伯海过渡层（ASTraL）的一部分：海气界面交换计划。通过该NSF奖项支持的四个船舶日将使十个站点的地球化学采样成为可能。2025年，一个为期四周的专门研究考察将集中在两个站的原位孵化率实验。将使用非原位和新型原位15N孵育，其保持自然痕量水平的O2浓度。还将进行动力学实验，以确定15 N标记孵育期间底物添加的影响。结合这些方法将揭示N2O生产和N2O消费的主导途径，以及微生物介导这些过程沿着垂直O2和生产力梯度在阿拉伯海ODZ。研究结果将允许有关更大规模的强迫和未来气候变化的影响的推论。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Nitrous oxide (N2O) is a powerful greenhouse gas, and a driver of ozone depletion in the stratosphere. Marine low-oxygen regions are important for N2O cycling and are a large source of N2O to the atmosphere. The Arabian Sea in the northwest Indian Ocean hosts one of the world’s largest low-oxygen zones, but it is less well-studied than other regions. In partnership with other researchers in the U.S. and India, this team will combine geochemical and microbial ecology approaches to study N2O cycling in the Arabian Sea. The project will support one postdoctoral investigator and two graduate students. Several undergraduate students will participate in the laboratory and at sea. One MS student from the Cochin University of Science and Technology (CUSAT), located in Kochi, Kerala, India will also be invited on at least one of the research cruises and participate in a 6-week internship in the Marine Stable Isotope Biogeochemistry Laboratory at the University of South Carolina. The U.S. postdoc and graduate students will participate in a 10-day regional training program in biogeochemistry for early career researchers in India. The project team will conduct public outreach from sea. They will also produce a freely available E-lecture on nitrogen cycling in low-oxygen zones.This project will advance current understanding of the microbiology and biogeochemistry of N2O production and consumption in marine oxygen deficient zones (ODZs) by quantifying rates and identifying major sources in the Arabian Sea using natural abundance stable isotopic and isotopomer data, 15N-labeled incubations, as well as genomic and metatranscriptomic methods. Field work is planned for the summers of 2024 and 2025. The first field activity will be during a cruise of opportunity funded by the Office of Naval Research (ONR) as part of the Arabian Sea Transition Layer (ASTraL): Exchange Across the Air-Sea Interface program. Four ship days supported through this NSF award will enable biogeochemical sampling at ten stations. In 2025, a four-week dedicated research expedition will focus on in-situ incubation rate experiments at two stations. Both ex-situ and novel in-situ 15N-incubations, which maintain natural trace-level O2 concentrations, will be used. Kinetic experiments will also be performed to determine the effect of substrate addition during 15N- labeled incubations. Combination of these approaches will reveal dominant pathways of N2O production and N2O consumption as well as the microorganisms mediating these processes along vertical O2 and productivity gradients in the Arabian Sea ODZ. Findings will allow inferences regarding larger scale forcings and impacts of future climate change.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.