Collaborative Research: In Situ Oxidation Rates of Methane Injected from Seafloor Gas Seeps

合作研究：海底气体渗漏注入甲烷的原位氧化速率

• 批准号: 1948720
• 负责人: Karen Lloyd
• 金额: $ 32.12万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-02-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1948720&HistoricalAwards=false
• 关键词: Collaborative; Research; Situ; Oxidation; Rates

Thousands of natural gas seeps have been discovered as streams of bubbles rising up from the seafloor just offshore from coastlines around the world. Extensive fields of seeps, largely releasing the same methane gas that we use to heat our homes, have recently been found about a hundred miles east of North Carolina’s Cape Hatteras at water depths as shallow as 300 feet. It is estimated that at least tens of thousands of these hydrocarbon-rich seeps occur on continental margins around the world. The seeps, usually seen as large rising plumes by sonar systems on research ships, inject huge, but poorly quantified, amounts of methane into overlying waters as they rise through the water column. A primary question is how much of the methane, a potent greenhouse gas, actually reaches the atmosphere. This question is the subject of much current research funded by several Federal research agencies including the National Science Foundation and the Department of Energy. Oceanographers believe that the methane (and other gases included in the bubble streams such as ethane and propane) are either transported away by ocean currents or consumed by microorganisms specially adapted to live with hydrocarbons as their main carbon source. This proposal seeks to determine the importance of microbial consumption in controlling methane distributions in the deep ocean and how the consumption rates depend on concentrations of methane, oxygen and other chemicals, as well as in situ pressures and temperatures. Previous studies in laboratories aboard research ship using samples returned to the surface suggest that microbial consumption of methane from the seeps may lag for a week after its injection into the water column and thus that physical dispersion by currents may dominate deepwater methane dynamics through dilution. However, other measurements suggest that there is no lag before aggressive microbial oxidation of injected methane begins. We have proposed to conduct in situ measurements of microbial methane consumption and related microbial community structure in bottom waters at several coastal and continental margin sites off the North Carolina coast and the northern Gulf of Mexico, where numerous natural seeps have also been observed. We will use new technologies developed after the release of massive quantities of methane during the Deepwater Horizon disaster in the Gulf. The sites offer varying concentrations of methane and other chemical and physical conditions such as oxygen concentrations and temperature that will allow us to test specific hypotheses about the role of microbial processes. Through performing the experiments with instruments right on the seafloor next to the seeps we can remove much of the uncertainty surrounding previous shipboard measurements. We will use newly developed seafloor landers equipped with advanced laser methane sensors that are capable of multi-week measurements while assaying dissolved oxygen, dissolved inorganic nitrogen and the microbial community for the presence of methane-consuming methanotrophs and their activity using advanced genomics techniques that can reveal the nature of methanotrophic responses to ambient methane concentrations. Successful collection of in situ methane consumption rate data and associated microbial community changes should prove important for modeling ocean methane dynamics over a range of oceanographic conditions including seep-enriched bottom waters and bottom waters impacted by accidental hydrocarbon releases.Graduate and undergraduate students supported by the project will gain critical skills in laboratory and field settings and will also benefit from frequent interactions with established researchers from diverse fields. Team members will participate in hands-on undergraduate education and training through developing individualized research projects leading to honors theses, presentations at national meetings and excellent graduate school placements. Graduate and undergraduates will also participate in K-12 science outreach efforts that help to attract and inform the next generation of oceanographers. The team will work with the University of North Carolina Morehead Planetarium and Science Center and participate directly in the North Carolina Science Festival. Through media contacts made from TED talks, exciting results will be broadly disseminated to the public. The project will have immediate relevance for understanding microbially mediated responses to hydrocarbon inputs from accidental releases along the Southeast Atlantic margin where oil and gas exploration are a constant topic of state and national policy discussions. Hundreds of recently discovered gas seeps along the continental margin offshore of Cape Hatteras, North Carolina plus thousands in the northern Gulf of Mexico, inject huge amounts of dissolved methane into overlying shelf and slope waters through dissolution of rising bubble plumes. The fate of the methane is largely controlled by a balance between microbial oxidation and advective transport away from seep sources. The efficacy of microbial oxidation likely depends on concentrations of methane, oxygen and ambient dissolved inorganic nitrogen (DIN), as well as in situ pressures and temperatures. Recent shipboard aerobic methane oxidation rate (AMOR) measurements suggest that microbial consumption of seep methane may lag for a week and thus physical dispersion could dominate deepwater methane dynamics through dilution. However, methane stable carbon isotopic measurements in bottom waters suggest that there is no lag before aggressive oxidation of injected methane begins. We propose to conduct in situ measurements of AMOR while simultaneously investigating its microbial drivers at representative North Carolina and Gulf of Mexico continental margin sites featuring numerous active bubble seeps. These sites offer varying concentrations of methane and DIN; performing the experiments in situ will remove much of the uncertainty of shipboard rates. We will conduct the measurements utilizing newly developed benthic lander systems equipped with advanced laser methane sensors that are capable of multi-week AMOR measurements while assaying dissolved oxygen, DIN and the microbial community for the presence of methanotrophs (through metagenomes) and their activity (through metatranscriptomes) that can reveal the nature of methanotrophic responses to ambient methane concentrations.The project will test key hypotheses about deep-sea methane dynamics including determining if there are significant lags in microbial responses after exposure to elevated methane concentrations, determining the relationships of AMOR to methane and DIN concentrations and investigating the response times and magnitude of methanotrophs to spatial and temporal variability in methane concentration. Successful collection of in situ AMOR and associated microbial community data will prove important for modeling ocean methane dynamics over a range of oceanographic conditions including seep-enriched bottom waters and accidental hydrocarbon releases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

成千上万的天然气被发现是因为从世界各地的海岸线从海底升起的气泡从海底升起。最近发现，在北卡罗来纳州北卡罗来纳州海角以东约100英里处的水深浅水处，较浅的渗水片大量释放了与我们用来加热房屋相同的甲烷气体的广泛田地。据估计，在世界各地的连续边缘上，至少有成千上万的这样的碳氢化合物渗透发生。这些发现，通常将声纳系统在研究船上被视为大幅上升的羽流，它们在水柱上升起时会注入大量但量化的甲烷。一个主要的问题是，实际上有多少甲烷，潜在的温室气体到达大气。这个问题是由国家科学基金会和能源部在内的几个联邦研究机构资助的许多当前研究的主题。海洋学家认为，诸如乙烷和丙烷等气泡流中的其他气体（以及其他气体）要么被洋流运输，要么被特别适应以碳氢化合物作为其主要碳源的微生物消耗。该提案旨在确定微生物消耗在控制深海中的甲烷分布中的重要性，以及消耗率如何取决于甲烷，氧和其他化学物质的浓度以及原位压力和温度。先前在研究船上使用样品返回表面的实验室的研究表明，从SEE的微生物消耗甲烷在将其注入水柱后可能会滞后一周，因此电流的物理分散可能会通过稀释来主导深水甲烷动力学。但是，其他测量结果表明，在侵袭性的甲烷注射侵袭性微生物氧化物开始之前，没有滞后。我们已经提议在北卡罗来纳州沿海几个沿海和连续的边缘地点和墨西哥北部的几个沿海和连续边缘地点的底部水域中的微生物甲烷消耗和相关微生物群落结构进行原位测量，还观察到许多自然渗漏。我们将使用海湾深水地平线灾难期间释放大量甲烷后开发的新技术。这些地点提供不同浓度的甲烷以及其他化学和物理条件，例如氧浓度和温度，这将使我们能够测试有关微生物过程作用的特定假设。通过用距离海底的仪器进行实验，我们可以消除围绕先前的船舶测量值的许多不确定性。我们将使用配备高级激光甲烷传感器的新开发的海底着陆器，这些传感器能够进行多周的测量，同时主张溶解的氧气，溶解的无机氮和微生物群落，以使用甲烷弥补的甲烷营养物及其活性，并使用先进的载量技术来揭示甲烷的含量反应，从而揭示出甲基化的甲基化技术。成功收集原位甲烷消耗率数据和相关的微生物群落变化对于在一系列海洋条件下建模的建模至关重要团队成员将通过开发个性化的研究项目来参加实践本科教育和培训。研究生和大学生还将参加K-12科学外展工作，以帮助吸引和告知下一代海洋学家。该团队将与北卡罗来纳大学莫尔黑德天文馆和科学中心合作，直接参加北卡罗来纳州科学节。通过TED谈话的媒体联系，令人兴奋的结果将大致传播给公众。该项目将立即与沿东南大西洋利润率的意外发行的微生物介导的反应有关，在该碳氢化合物输入中，石油和天然气勘探是国家和国家政策讨论的一个始终的话题。数百种最近发现的气体沿着北卡罗来纳州哈特拉斯角的连续边缘沿近海以及墨西哥湾北部的成千上万的气体看到，通过溶解升起的气泡羽毛，将大量溶解的甲烷溶解在上覆的架子和斜坡上。甲烷的命运主要由微生物氧化与主动转运之间的平衡控制。微生物氧化的效率可能取决于甲烷，氧和环境溶解的无机氮（DIN）以及原位压力和温度的浓度。最近的船上有氧甲烷氧化速率（AMOR）的测量表明，微生物的渗水甲烷的消耗可能滞后一周，因此物理分散可能会通过稀释而主导深水甲烷动力学。然而，底水中的甲烷稳定的碳同位素测量表明，在注射甲烷的侵袭性氧化开始之前，没有滞后。我们建议对Amor进行原位测量，同时研究其微生物驱动因素，代表墨西哥的北卡罗来纳州和墨西哥湾连续缘缘地点，具有许多活跃的气泡渗漏。这些地点提供不同浓度的甲烷和DIN。在原位进行实验将消除船上费率的大部分不确定性。我们将使用配备高级激光甲烷传感器的新开发的底栖降落器系统进行测量，这些系统能够进行多周的摩擦测量，同时分析溶解的氧气，DIN和微生物群落，以表明存在甲烷营养型（通过甲烷营养不良）及其活性（通过甲基转化型甲基甲基甲基甲基苯酚）的性质（通过甲基苯酚验证）的性质，可以揭示出甲基甲基甲基苯丙胺的性质。关于深海甲烷动力学的关键假设，包括确定暴露于甲烷浓度升高后的微生物反应中是否存在明显的滞后，确定甲烷与甲烷和DIN浓度的关系以及研究甲烷浓度中甲烷营养物与空间和临时变异性的反应时间和大小。成功收集原位和相关的微生物群落数据将证明对于在一系列海洋条件下建模包括透明的底部水和意外的碳氢化合物发行版，这将被证明是重要的。该奖项反映了NSF的法定任务，并通过使用该基金会的知识分子优点和广泛的影响来评估NSF的法定任务。