Collborative Research: Laboratory Investigation of Redox Reactions during Subsurface Mixing in Submarine Hydrothermal Systems

位于大洋扩张中心的海底温泉是由于火山活动产生的热量而形成的，火山活动是新洋壳形成的原因。当海水在海洋地壳中循环时，海水被加热到高达400°C的温度，导致广泛的化学反应，将流体的成分改变为酸性，富含金属和硫化物，并且高度还原。这些流体在海底排放并与海水混合，创造了一个支持大型微生物生态系统的化学环境，这些生态系统不依赖太阳（光合作用）作为能源。相反，它们是通过催化化学反应来维持的，这些化学反应发生在热的和还原的热液流体与冷的氧化海水混合时。微生物利用这些反应作为能量来源的能力高度依赖于参与这些类型的氧化还原反应的化合物的丰度和组成。这项研究进行了实验室实验，以确定非生物（即，不涉及生命）产生或消耗深海微生物所用的化合物的化学反应。这些数据提高了我们对地下微生物和高阶海洋生态系统的理解，这些生态系统依赖这些微生物作为食物网的基础，在海面以下数千英尺的海底底部茁壮成长。这项工作的更广泛影响包括一个实质性的教育组成部分，通过与一个主要的海洋学研究机构（伍兹霍尔海洋学研究所）的伙伴关系，为一个以本科为主的机构（布里奇沃特州立大学）的25个本科理科专业提供最先进的研究经验。这种研究和教育的整合包括研究课程的开发和实施，在布里奇沃特州立大学提供，并在伍兹霍尔密集的夏季研究经验。目的是为本科生提供机会，体验科学过程的各个方面，包括背景研究，数据收集，分析和解释，并在全国会议上介绍结果，以便更好地为就业和研究生学习做好准备。这项研究包括实验室实验，调查海底热液系统地下混合区的非生物氧化还原反应。使用新型实验室反应器，实验研究海水中关键氧化还原反应物种之间的化学不平衡（例如，H2、H2S、Fe 2+、CH 4、O2、SO 42-、CO2、NO3-），它们构成了支持复杂地下生态系统的化学能的主要来源。目前，这种反应在热液环境中的约束很差，因此这项工作确定了这些反应，并确定了它们在低至中等温度下的速率，这些温度是热液系统中地下混合区的特征。由此产生的数据将有助于改进热液喷口微生物代谢途径的模型。实验将使用一个开放系统流通式反应池进行，该反应池能够根据温度和pH值调节H2、O2、H2S、NO3-和中间氧化态硫和氮物质的浓度。这将有助于更好地了解化学环境与生物群落的组成和功能之间的联系。

Submarine hot-springs at oceanic spreading centers form in response to heat associated with volcanic activity responsible for the creation of new oceanic crust. This heating of seawater to temperatures as high as 400°C, as it circulates through the ocean crust, results in extensive chemical reactions that modify the fluid's composition to something that is acidic, metal- and sulfide-rich, and highly reducing. Venting of these fluids at the seafloor and mixing with seawater creates a chemical environment that supports large microbial ecosystems that do not rely on the sun (photosynthesis) as a source of energy. Instead, they are sustained by catalyzing chemical reactions that occur when hot and reduced hydrothermal fluids mix with cold oxidized seawater. The ability of microbes to utilize these reactions as an energy source is highly dependent on the abundance and composition of chemical compounds that participate in these types of oxidation-reduction reactions. This research conducts laboratory experiments to determine the rate of abiotic (i.e., not involving life) chemical reactions that produce or consume chemical compounds used by deep sea microbes. These data improve our understanding of how subsurface microbes and the higher order marine ecosystems, that rely on these microbes as the base of the food web, thrive on the bottom of the seafloor thousands of feet below the sea surface. Broader impacts of the work include a substantial educational component that provides state-of-the-art research experiences for 25 undergraduate science majors at a primarily undergraduate institution (Bridgewater State University) through partnership with a major oceanographic research institution (the Woods Hole Oceanographic Institution). This integration of research and education includes the development and implementation of a research course, offered at Bridgewater State, and intensive summer research experiences at Woods Hole. The goal is to provide undergraduates with opportunities to experience all aspects of the scientific process, including background research, data collection, analysis and interpretation, and presentation of results at a national conference in order to better prepare them for employment and graduate study.This research consists of laboratory experiments that investigate abiotic redox reactions in subsurface mixing zones in seafloor hydrothermal systems. Using a novel laboratory reactor, experiments investigate chemical disequilibria between key redox reactive species in seawater (e.g., H2, H2S, Fe2+, CH4, O2, SO42-, CO2, NO3-), which comprise a major source of chemical energy that supports complex subsurface ecosystems. At present, such reactions are poorly constrained in hydrothermal environments, so this work identifies these reactions and determines their rates at low to moderate temperatures that characterize subsurface mixing zones within hydrothermal systems. The resulting data will allow improvement of models of hydrothermal vent microbial metabolic pathways. Experiments will take place using an open-system flow-through reaction cell that is able to regulate the concentration of H2, O2, H2S, NO3-, and intermediate oxidation state sulfur and nitrogen species as a function of temperature and pH. Data will be used to place fundamental constraints on thermodynamic models used to predict the amount of chemical energy delivered to vent ecosystems, which should lead to an improved understanding of the linkages between chemical environment and biological community composition and function.