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

__________________________________________________________________________________________ 需氧微生物在海洋里帮助调节生物地球化学的养分循环通过连接生产和消费的溶解氧(做)和有机物质。已证明，深海中DO的浓度正在稳步下降，因此，DO含量极低的区域，即氧最小区正在扩大。虽然这一现象被认为对生物地球化学循环有潜在的严重影响，但令人惊讶的是，很少有研究来确定影响这些变化的机制和量化具体过程。该项目将研究海洋内部DO浓度变化与养分循环之间的联系。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的海洋生物地球化学反应的复杂性和关联性，每一个反应都可能因浓度变化而改变，因此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。该项目将通过开发教材来教授高中学生氮循环，通过为本科生开发海洋化学基础课程，为他们提供实地和计算经验，并通过建立过去的努力，将传统上未被充分代表的科学群体包括在内，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，并将其发布到互联网上，以增加少数民族学生的可访问性。世界上最大的氧最小带（OMZ）位于热带北太平洋东部（ETNP），是研究不同溶解氧（DO）浓度对内陆海洋养分循环影响的理想研究场所。在整个OMZ中，缺氧程度展示了一个范围，允许研究改变DO含量对“真实世界”环境中好氧微生物控制DO和有机物消耗的速率和机制的影响。特别是在氮循环中起关键作用的氨氧化和亚硝酸盐氧化反应，可能会受到DO浓度变化的显著影响。该项目将评估ETNP各个站点的有氧呼吸、氨和亚硝酸盐氧化率，仔细检查控制的孵育，并开发引物以靶向OMZ中的活性微生物；所有这些都是为了量化DO和这些生物地球化学营养循环之间的联系。该研究还将检验在低DO和浅OMZ水域中呼吸的有机碳比之前认为的要多的假设，并评估低DO区域的氮循环可能会使OMZ由于亚硝酸盐氧化和硝酸盐还原而缺氧，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，更充分地了解这些不同的、复杂的组成部分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.