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循环很重要，是大气中N2O的一大来源。印度洋西北部的阿拉伯海拥有世界上最大的低氧区之一，但与其他地区相比，对它的研究较少。该小组将与美国和印度的其他研究人员合作，结合地球化学和微生物生态学方法研究阿拉伯海的一氧化二氮循环。该项目将资助一名博士后研究员和两名研究生。几名本科生将参加实验室和海上。来自印度喀拉拉邦科钦科技大学（CUSAT）的一名硕士学生也将被邀请参加至少一次研究巡航，并在南卡罗莱纳大学海洋稳定同位素生物地球化学实验室进行为期6周的实习。美国博士后和研究生将在印度参加一个为期10天的生物地球化学区域培训项目，该项目面向早期职业研究人员。项目团队将从海上开展公众宣传活动。他们还将制作一个免费的关于低氧区氮循环的电子讲座。该项目将通过使用自然丰度稳定同位素和同位素数据、15n标记培养以及基因组学和亚转录组学方法，量化速率并确定阿拉伯海N2O的主要来源，从而推进目前对海洋缺氧区（odz） N2O生产和消耗的微生物学和生物地球化学的理解。现场工作计划在2024年和2025年夏季进行。第一次现场活动将在由海军研究办公室（ONR）资助的机会巡航期间进行，作为阿拉伯海过渡层（ASTraL）：跨海空界面交换计划的一部分。美国国家科学基金会资助的4个航天将在10个站点进行生物地球化学采样。2025年，一个为期四周的专门研究考察将集中在两个站点的原位孵化率实验。将使用非原位和新型原位15n孵育，它们保持天然痕量O2浓度。动力学实验也将进行，以确定底物添加在15N标记的孵育期间的影响。这些方法的结合将揭示N2O产生和消耗的主要途径，以及在阿拉伯海ODZ沿垂直O2和生产力梯度介导这些过程的微生物。研究结果将有助于推断更大规模的强迫和未来气候变化的影响。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。

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.