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

海洋中的__________________________________________________________________________________________Aerobic微生物通过相关的溶解氧(DO)和有机物的生产和消耗来帮助调节生物地球化学营养循环。在更深的海洋水域，DO浓度已被证明是稳步下降的，由此产生的DO含量极低的区域，即所谓的氧气最小区域(OMZ)，正在扩大。虽然这一现象被认为对OMZ正在增长的生物地球化学循环具有潜在的严重影响，但令人惊讶的是，几乎没有人进行研究来确定影响这些变化的机制和具体过程。该项目将研究DO浓度变化与海洋内部营养循环之间的联系。氮化合物(尤其是氨氮和亚硝酸盐)的氧化受DO浓度的影响很大。由于涉及DO的海洋生物地球化学反应的复杂和相互关联的性质，每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。该项目将把教育纳入研究，方法是开发向高中生传授氮循环知识的材料，为本科生开发一门基于海洋化学的课程，为他们提供实地和计算经验，以及在过去努力的基础上，将传统上代表性不足的群体纳入科学领域。该项目资助的一名研究生将把讲座翻译成西班牙语，并在互联网上提供给少数族裔学生，以增加他们的可及性。世界上最大的氧气最小区(OMZ)位于东热带北太平洋(ETNP)，是研究不同溶解氧(DO)浓度对内海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含量对好氧微生物在真实世界中控制DO和有机物消耗的速率和机制的影响。特别是，氨和亚硝酸盐氧化，这两个在氮循环中起关键作用的反应，可能会受到不同DO浓度的显著影响。该项目将评估ETNP中不同站点的好氧呼吸、氨和亚硝酸盐氧化速率，检查仔细控制的培养，并开发针对OMZ中活跃微生物的底物；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。这项研究还将检验这一假设，即在低DO和浅OMZ水域呼吸的有机碳比之前认为的更多，并评估低DO地区的氮循环可能会由于亚硝酸盐氧化和硝酸盐还原而推动OMZ进入缺氧状态，这可能会加速DO的消耗。随着OMZ在不断变化的海洋中的扩张，更充分地了解这些不同、复杂的组件之间的联系是至关重要的。

__________________________________________________________________________________________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.