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

一氧化二氮（N2 O）在大气中的浓度很低，但却是一种重要的温室气体和臭氧破坏物质。与甲烷和二氧化碳等其他气候活性气体一样，人类活动直接通过化石燃料燃烧或农业活动对其大部分生产负责。 然而，大约三分之一的自然N2 O排放来自海洋，但即使是这些排放也会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。 这三个海洋区域是中间深度氧浓度如此之低的地方，以至于需要缺氧的代谢过程能够发生。 这些区域被称为氧气最小区（OMZ），它们具有全球海洋沃茨中其他地方没有的微生物过程。 在这里提出的工作中，我们将研究如何N2 O的生产和消费的微生物途径是由环境条件，如氧气和营养浓度调节。 这项工作将包括对其中一个大洋隔离区-墨西哥海岸外的东热带太平洋-进行一次研究考察。 在游轮上，我们将在普林斯顿大学和斯坦福大学的家庭实验室进行实验并收集样本进行分析。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挂钩。这项工作是特别及时的，因为全球变暖已经间接影响了OMZ的大小和地理范围。 更大范围的低氧水可能导致N2 O的产生增加，导致N2 O向大气的通量增加。 在大气层中，一氧化二氮在破坏臭氧方面的作用以及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（N2 O）是一种重要的温室气体和臭氧破坏物质。 约三分之一的N2 O天然排放来自海洋，约一半的海洋排放源来自具有缺氧中间沃茨（最小氧区，OMZ）的沃茨。 硝化作用被认为是海洋中N2 O的主要来源，但反硝化作用也可能是OMZ及其周围的净来源。由于硝化和反硝化是由具有非常不同的代谢和环境控制的微生物进行的，因此它们对N2 O产生的贡献预计会因氧合和营养输入的变化而不同。 因此，重要的是要了解这两个过程的N2 O生产的调节。 该项目的主要目标是量化的N2 O的生产和消费途径的环境监管和周围的OMZ，以获得预测性的了解N2 O在海洋中的分布和通量。要做到这一点，N2 O的生产和消费将使用稳定的同位素示踪剂培养在位于东部热带北太平洋的主要OMZ之一内外的站点进行测量。将确定速率过程对底物、产物和氧浓度的依赖性，并评估微生物组合物的组成，以确定在不同环境条件下是否涉及不同的微生物组分。 自然丰度稳定同位素和同位素测量的N2 O将被解释与测得的速率，以推断来源和途径（硝化，硝化反硝化，反硝化，和？混血儿？N2 O的生产和消费。这项工作还将涉及一种新的应用同位素测量N2 O从孵化，以确定15 N的位置从NH 4+和NO2-标记N2 O池内。OMZ区域是独特的氮循环过程的场所，这对于确定海洋的固定氮库存至关重要。如果OMZ在未来几十年内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一氧化二氮的大气通量，并通过固定氮库存的变化来改变整体海洋生产力。了解N2 O生产和消费过程的监管和环境控制是了解其对全球变化反应的基础。

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.