CAREER: Oxygen sensitivity of aerobic respiration and nitrification in oxygen minimum zones and biogeochemical feedbacks to deoxygenation

_海洋中的好氧微生物通过溶解氧（DO）和有机物的产生和消耗来帮助调节海洋地球化学营养循环。在深海沃茨中，溶解氧浓度已显示出稳步下降的趋势，由此产生的溶解氧含量极低的区域，即所谓的最低含氧区（OMZ）正在扩大。虽然这一现象被认为对有机磁区生长的地球化学循环具有潜在的严重影响，但令人惊讶的是，几乎没有研究来确定影响这些变化的机制和量化具体过程。该项目将研究溶解氧浓度变化与海洋内部营养循环之间的联系。含氮化合物（特别是氨和亚硝酸盐）的氧化受到DO浓度的强烈影响。由于涉及DO的海洋生物化学反应的复杂性和关联性，每一个都可能因浓度变化而改变，这项研究对于全面了解海洋化学在不久的将来将如何变化至关重要。该项目将通过开发材料来向高中生教授氮循环，通过为本科生开发海洋化学课程，为他们提供实地和计算经验，并通过过去的努力将传统上代表性不足的群体纳入科学，将教育纳入研究。该项目资助的一名研究生将把讲座翻译成西班牙语，并将其发布在互联网上，以增加少数民族学生的可访问性。位于热带北太平洋东部（ETNP）的世界上最大的最低含氧区（OMZ）是研究不同溶解氧（DO）浓度对海洋内部营养循环影响的理想研究地点。在整个OMZ中，缺氧的程度表现出一个范围，允许研究改变DO含量对控制好氧微生物在“真实的世界”环境中消耗DO和有机物的速率和机制的影响。特别是，氨和亚硝酸盐的氧化，在氮循环中发挥关键作用的反应，可能会受到显着影响，通过不同的DO浓度。该项目将评估ETNP各站的有氧呼吸、氨和亚硝酸盐氧化速率，检查仔细控制的孵育，并开发针对OMZ中活性微生物的引物;所有这些都是为了量化DO与这些生物地球化学营养循环之间的联系。该研究还将检验以下假设，即在低DO和浅OMZ的沃茨中呼吸的有机碳比以前认为的更多，并评估低DO区域的氮循环可能会由于亚硝酸盐氧化加上硝酸盐还原而将OMZ推向缺氧的可能性，这可能会加速DO的消耗。随着OMZ在不断变化的海洋中的扩展，更全面地了解这些各种复杂组件之间的联系至关重要。

__________________________________________________________________________________________Aerobic microorganisms in the ocean help regulate biogeochemical nutrient cycles through the linked production and consumption of dissolved oxygen (DO) and organic matter. Concentrations of DO have been shown to be steadily decreasing in deeper ocean waters and the resulting areas of critically low DO content, known as oxygen minimum zones (OMZs), are expanding. While this phenomenon is recognized as having potentially serious impacts on biogeochemical cycles where OMZs are growing, surprisingly little research has been done to identify the mechanisms and quantify the specific processes that will affect these changes. This project will study the connection between changing DO concentrations and nutrient cycling in the interior of the ocean. The oxidation of nitrogen compounds (ammonia and nitrite in particular) is strongly influenced by DO concentrations. Because of the complex and connected nature of marine biogeochemical reactions that involve DO, each one potentially altered by concentration changes, this research is critical for a complete understanding of how ocean chemistry will change in the near future. The project will incorporate education into the research by developing materials to teach high school students about the nitrogen cycle, by developing a marine chemistry based course for undergraduates that will give them both field and computational experience, and by building on past efforts to include traditionally underrepresented groups in science. One of the graduate students funded by this project will translate lectures into Spanish and make these available on the internet for increased accessibility for minority students.The world's largest oxygen minimum zone (OMZ), located in the Eastern Tropical North Pacific (ETNP), is an ideal study site for research into the effects of varying dissolved oxygen (DO) concentrations on nutrient cycling in the interior ocean. Throughout this OMZ, the extent of anoxia exhibits a range that allows for study of the effect of changing DO content on the rates and mechanisms that control consumption of DO and organic matter by aerobic microorganisms in a 'real world' setting. In particular, ammonia and nitrite oxidation, reactions that play a critical role in the nitrogen cycle, are likely to be significantly affected by varying DO concentration. This project will evaluate aerobic respiration, ammonia, and nitrite oxidation rates at various stations in the ETNP, examine carefully controlled incubations, and develop primers to target active microorganisms in the OMZ; all to quantify the connections between DO and these biogeochemical nutrient cycles. The research will also examine the hypothesis that more organic carbon is respired in waters with low DO and a shallow OMZ than previously thought and evaluate the possibility that nitrogen cycling in low DO regions could push OMZs to anoxia due to nitrite oxidation coupled with nitrate reduction, which could potentially accelerate DO consumption. With the expansion of OMZ's in a changing ocean, it is crucial to more fully understand the connections between these various, complex, components.