Collaborative Research: Mechanisms and Controls of Nitrous Oxide Production in the Eastern Tropical North Pacific Ocean

一氧化二氮(N2O)在大气中的浓度很低，但它是一种重要的温室气体和破坏臭氧的物质。与甲烷和二氧化碳等其他会引起气候变化的气体一样，人类活动产生了大部分二氧化碳，要么是直接通过化石燃料燃烧，要么是通过农业活动。然而，大约三分之一的自然N2O排放来自海洋，但即使是这些排放也可能受到人类活动的间接影响。大约一半的海洋来源来自太平洋和阿拉伯海的三个特定地理区域。这三个大洋区域在中等深度的氧气浓度非常低，以至于需要氧气的新陈代谢过程才能发生。这些区域被称为氧气最小区域(OMZ)，它们具有全球海水中其他地方没有的微生物过程。在这里提出的工作中，我们将调查N2O产生和消耗的微生物途径是如何受环境条件(如氧气和营养浓度)调节的。这项工作将涉及对OMZ之一的研究探险，即墨西哥海岸外的东热带太平洋。在邮轮上，我们将进行实验，并收集样本，在普林斯顿大学和斯坦福大学的家庭实验室进行分析。这两个机构的研究生咨询和研究生和本科生教学将与这项研究联系起来。这项工作特别及时，因为全球变暖已经间接影响了海洋保护区的大小和地理范围。更大范围的低氧水可能会导致N2O产生增加，导致N2O进入大气的通量增加。在大气中，N2O在破坏臭氧和作为温室气体的作用可能是全球变化的关键因素。一氧化二氮(N2O)是一种重要的温室气体和臭氧破坏物质。大约三分之一的自然N2O排放来自海洋，大约一半的海洋来源来自缺氧的中间水域(氧气最低限度区域，OMZ)。硝化作用被认为是海洋中N2O的主要来源，但反硝化作用也可能对OMZ及其周围的净源做出贡献。由于硝化和反硝化作用是由具有非常不同的新陈代谢和环境控制的微生物执行的，因此它们对N2O产生的贡献预计会随着氧合作用和养分输入的变化而不同。因此，了解这两种工艺对N2O产生的调节是很重要的。该项目的主要目标是量化海洋保护区内和周围的N2O生产和消费路径的环境调节，以获得对海洋中N2O分布和通量的预测性了解。为此，将在东热带北太平洋的一个主要海洋保护区内外的站点使用稳定的同位素示踪剂培养来测量N2O的生产和消费。将确定速率过程对底物、产物和氧气浓度的依赖关系，并将评估微生物组合的组成，以确定不同环境条件下是否涉及不同的微生物成分。N2O的自然丰度稳定同位素和同位素异构体的测量结果将与测量的速率相一致地进行解释，以推断N2O的来源和途径(硝化、硝化-反硝化、反硝化和混合？形成)参与了N2O的生产和消费。这项工作还将涉及从培养中测量N2O的同位素测量的新应用，以确定来自NH4和NO2-的15N在标记的N2O池中的位置。OMZ区域是独特的氮循环过程的地点，这对确定海洋的固定氮库存至关重要。如果海洋保护区在未来几十年由于人为变化而如预测的那样扩大，这些化学分布的变化可能会影响大气中一氧化二氮的通量，并通过固定氮库存的变化来改变总体海洋生产力。了解负责N2O生产和消费的过程的监管和环境控制是了解它们对全球变化的反应的基础。

Nitrous oxide (N2O) is present at very low concentrations in the atmosphere but is an important greenhouse gas and ozone destroying substance. As with other climate-active gases like methane and carbon dioxide, human activities are responsible for most of its production, either directly through fossil fuel burning or agricultural activities. However, about a third of natural N2O emissions come from the ocean, but even these emissions can be indirectly affected by human activities. About half of the ocean source is derived from three specific geographic regions in the Pacific Ocean and Arabian Sea. These three oceanic regions are places where oxygen concentrations are so low in the intermediate depths that metabolic processes requiring the absence of oxygen are able to occur. These regions are called Oxygen Minimum Zones (OMZs) and they have microbiological processes that occur nowhere else in global ocean waters. In the work proposed here, we will investigate how the microbiological pathways of N2O production and consumption are regulated by environmental conditions such as oxygen and nutrient concentration. This work will involve a research expedition to one of the OMZs, the Eastern Tropical Pacific Ocean off the coast of Mexico. On the cruise, we will perform experiments and collect samples for analysis in our home laboratories at Princeton and Stanford Universities. Advising of graduate students and teaching at the graduate and undergraduate levels at both institutions will be linked to this research. This work is particularly timely because global warming has already indirectly affected the size and geographic extent of the OMZs. Greater expanse of low oxygen water could cause N2O production to increase, leading to increased fluxes of N2O to the atmosphere. In the atmosphere, the role of N2O in ozone destruction and as a greenhouse gas could be critical elements of global change. Nitrous oxide (N2O) is an important greenhouse gas and ozone destroying substance. About a third of natural N2O emissions come from the ocean, and about half of the ocean source is derived from waters with oxygen deficient intermediate waters (oxygen minimum zones, OMZs). Nitrification is recognized as the main source of N2O in the ocean, but denitrification also likely contributes to the net source in and around OMZs. Because nitrification and denitrification are performed by microbes with very different metabolisms and environmental controls, their contributions to N2O production are expected to differ in response to changes in oxygenation and nutrient inputs. Thus it is important to understand the regulation of N2O production by both processes. The main goal of this project is to quantify the environmental regulation of N2O production and consumption pathways in and around OMZs in order to obtain predictive understanding of N2O distributions and fluxes in the ocean. To do this, production and consumption of N2O will be measured using stable isotope tracer incubations at stations located within and outside one of the major OMZs in the Eastern Tropical North Pacific ocean. The dependence of the rate processes on substrate, product, and oxygen concentrations will be determined, and the composition of the microbial assemblages will be assessed to determine whether different microbial components are involved under different environmental conditions. Natural abundance stable isotope and isotopomer measurements of N2O will be interpreted in concert with measured rates to deduce the sources and pathways (nitrification, nitrifier-denitrification, denitrification, and ?hybrid? formation) involved in N2O production and consumption. This work will also involve a novel application of isotopomer measurements of N2O from incubations to identify the placement of 15N from NH4+ and NO2- within labeled N2O pools. OMZ regions are the sites of unique nitrogen cycling processes that are critical in determining the fixed nitrogen inventory of the ocean. If OMZs expand as predicted due to anthropogenic changes in the coming decades, changes in these chemical distributions may affect the atmospheric flux of nitrous oxide as well as modify overall ocean productivity via changes in the fixed nitrogen inventory. Understanding the regulation and environmental control of the processes responsible for N2O production and consumption is the foundation of understanding their response to global change.