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气候活跃气体一样，人类活动直接通过化石燃料燃烧或农业活动产生了大部分温室气体。然而，大约三分之一的天然一氧化二氮排放来自海洋，但即使是这些排放也会受到人类活动的间接影响。大约一半的海水来源来自太平洋和阿拉伯海的三个特定地理区域。在这三个海洋区域，中间深度的氧浓度非常低，以至于需要缺氧的代谢过程能够发生。这些区域被称为氧最小带（OMZs），它们有全球其他海域没有的微生物过程。在这里提出的工作中，我们将研究N2O生产和消耗的微生物途径如何受到氧气和养分浓度等环境条件的调节。这项工作将包括对omz之一的研究考察，即墨西哥海岸外的东热带太平洋。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和收集样本进行分析。这两所大学的研究生指导以及研究生和本科生的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。低氧水的更大范围可能导致N2O产量增加，从而导致N2O向大气的通量增加。在大气中，一氧化二氮在破坏臭氧和作为温室气体中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。大约三分之一的天然一氧化二氮排放来自海洋，大约一半的海洋源来自缺氧的中间水域（最低氧区，OMZs）。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是海洋中及其周围N2O的净来源。由于硝化和反硝化是由代谢和环境控制非常不同的微生物进行的，因此它们对N2O产生的贡献预计会随着氧合和养分输入的变化而有所不同。因此，了解这两种工艺对N2O生产的调节是很重要的。该项目的主要目标是量化omz及其周围N2O生产和消费途径的环境调节，以获得对海洋中N2O分布和通量的预测性理解。为此，将利用稳定同位素示踪剂孵育在东热带北太平洋一个主要海洋保护区内外的站点测量一氧化二氮的生产和消耗。将确定速率过程对底物、产物和氧浓度的依赖性，并评估微生物组合的组成，以确定在不同的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体测量值将与测量速率相一致进行解释，以推断来源和途径（硝化作用、硝化-反硝化作用、反硝化作用和混合硝化作用）。形成)参与N2O的生产和消费。这项工作还将涉及一种新的应用，即同位素体测量培养皿中的N2O，以确定NH4+和NO2-中的15N在标记的N2O池中的位置。OMZ区域是独特的氮循环过程的场所，这对确定海洋的固定氮库存至关重要。如果由于未来几十年的人为变化，omz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氧化亚氮的通量，并通过固定氮储量的变化改变海洋的整体生产力。了解一氧化二氮生产和消费过程的监管和环境控制是了解其对全球变化响应的基础。

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.