Expression of Microbial Nitrification in the Stable Isotopic Systematics of Oceanic Nitrite and Nitrate

关闭海洋硝酸盐和氧化亚氮的预算是对初级生产力和气候变化中营养驱动变化感兴趣的研究人员的中心目标。随着海水硝酸盐氧同位素分析新方法的实施，基于其氧同位素分布构建硝酸盐预算将成为氮同位素预算的补充。在我们能够有效地利用硝酸盐中的氧同位素来了解目前对海洋氮循环的理解之前，我们必须首先了解产生（硝化）和消耗（同化，反硝化）硝酸盐的不同过程如何影响其氧同位素特征。在这项研究中，伍兹霍尔海洋研究所的研究人员将对该领域硝化作用的氧同位素系统进行定量评估，从而填补我们对硝酸盐、亚硝酸盐和氧化亚氮的18O变化的理解的关键空白。主要目标是对海洋硝化过程中产生的亚硝酸盐和硝酸盐的氧同位素特征进行定量预测。研究人员推测，硝化过程中的氧同位素分馏是决定新生成的硝酸盐和亚硝酸盐18O值的主要因素。其次，他们假设在氨氧化和亚硝酸盐氧化紧密耦合的地方氧原子交换很低，但在亚硝酸盐富集的区域，如初级和次级亚硝酸盐的最大值处，氧原子交换可能会增加。他们将通过一系列有针对性的实验室和实地实验，以及亚硝酸盐和硝酸盐同位素分布的测量来检验这些假设，这些分布延伸到热带南太平洋东部的泛光带、初级亚硝酸盐最大值和次级亚硝酸盐最大值。这些实验的结果有望为在潜在微生物过程背景下解释亚硝酸盐、硝酸盐和N2O中18O同位素特征提供所需的基本信息。更好地了解这些特征和相关过程对于量化海洋中的新产量、氮收支控制和N2O产量非常重要，这将有助于更好地理解氮循环、海洋化学和气候之间的直接和间接相互作用。更广泛的影响：这项研究的结果应该引起对海洋氮循环、N2O生产、气候变化以及硝化菌生理和生物化学感兴趣的广泛研究团体的兴趣。学生在生物地球化学方面的培训将是该活动的一个重要组成部分。一名女研究生将参与整个项目，并将学习将培养操作、实验室和实地研究以及同位素和数据采集与分析方面的训练结合起来。本科生也将有机会参与其中，包括来自代表性不足的少数群体的学生。

Closing the marine budgets of nitrate and nitrous oxide are central goals for researchers interested in nutrient-driven changes in primary productivity and climate change. With the implementation of new methods for oxygen isotopic analysis of seawater nitrate, it will be possible to construct a budget for nitrate based on its oxygen isotopic distribution that is complementary to nitrogen isotope budgets. Before we can effectively use oxygen isotopes in nitrate to inform the current understanding of the marine nitrogen cycle, we must first understand how different processes that produce (nitrification) and consume (assimilation, denitrification) nitrate affect its oxygen isotopic signature. In this study, researchers at the Woods Hole Oceanographic Institution will provide a quantitative assessment of the oxygen isotopic systematics of nitrification in the field and thus fill a key gap in our understanding of 18O variations in nitrate, nitrite, and nitrous oxide. The primary goal is to develop a quantitative prediction of the oxygen isotopic signatures of nitrite and nitrate produced during nitrification in the sea. The researchers hypothesize that oxygen isotopic fractionation during nitrification is the primary factor setting the 18O values of newly produced nitrate and nitrite. Secondly, they hypothesize that oxygen atom exchange is low where ammonia oxidation and nitrite oxidation are tightly coupled, but may increase in regions with nitrite accumulation, such as in the primary and secondary nitrite maxima. They will test these hypotheses with a series of targeted laboratory and field experiments, as well as with measurements of nitrite and nitrate isotopic distributions extending through the euphotic zone, primary nitrite maximum, and secondary nitrite maximum of the Eastern Tropical South Pacific. The results of these experiments are expected to provide fundamental information required for the interpretation of 18O isotopic signatures in nitrite, nitrate, and N2O in the context of underlying microbial processes. A better understanding of these features and the processes involved is important for quantifying new production, controls on the N budget, and N2O production in the ocean -- which should lead to a better understanding of the direct and indirect interactions among the nitrogen cycle, marine chemistry, and climate. Broader Impacts: The results of this research should be of interest to a broad research community interested in oceanic nitrogen cycling, N2O production, and climate change, as well as nitrifier physiology and biochemistry. Student training in biogeochemistry will be an important component of the activity. A female graduate student will participate throughout this project, and will learn to integrate training in culture manipulation, laboratory and field-going research, as well as isotopic and data acquisition and analysis. There will also be opportunities for undergraduate students, including ones from under-represented minority groups, to become involved.