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.

最近，人们发现了数以千计的天然气渗漏点，大量气泡从世界各地海岸线附近的海底升起，这些渗漏点主要释放出与我们用来为房屋供暖相同的甲烷气体。北卡罗来纳州哈特拉斯角以东百英里处，水深浅至 300 英尺。据估计，世界各地的大陆边缘至少有数万处此类富含碳氢化合物的渗漏点。研究船上的声纳系统将其视为大量上升的羽流，当它们上升穿过水柱时，会向上层水域注入大量但难以量化的甲烷，一个主要问题是，有多少甲烷（一种强效温室气体）实际上到达了上层水域。这个问题是由包括国家科学基金会和能源部在内的多个联邦研究机构资助的许多当前研究的主题，他们认为甲烷（以及气泡流中包含的其他气体，例如乙烷和丙烷）。要么被洋流带走，要么被专门适应以碳氢化合物为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甲烷分布方面的重要性，以及消耗率如何取决于碳氢化合物的浓度。甲烷、氧气和其他化学物质，以及研究船实验室先前使用返回地表的样本进行的研究表明，微生物对渗漏中甲烷的消耗可能会滞后一周。然而，其他测量表明，在注入甲烷的剧烈微生物氧化开始之前，水流的物理扩散可能会主导深水甲烷动力学。我们将使用开发的新技术，研究北卡罗来纳州海岸和墨西哥湾北部几个沿海和大陆边缘地点的底部水域的消耗和相关微生物群落结构，这些地方也观察到了许多自然渗漏。在海湾深水地平线灾难期间释放大量甲烷后，这些地点提供了不同浓度的甲烷以及其他化学和物理条件，例如氧气浓度和温度，这将使我们能够测试有关微生物过程作用的具体假设。通过在渗漏点附近的海底进行实验，我们可以消除之前船上测量的大部分不确定性，我们将使用配备先进激光甲烷传感器的新开发的海底着陆器，这些传感器能够在分析时进行数周的测量。溶解氧，使用先进的基因组学技术，可以揭示甲烷氧化菌对环境甲烷浓度的反应的性质，并成功收集原位甲烷消耗率数据和相关的微生物群落变化。事实证明，这对于模拟一系列海洋条件下的海洋甲烷动力学非常重要，包括富含渗流的底层水和受意外碳氢化合物释放影响的底层水。该项目支持的研究生和本科生将获得实验室和现场环境中的关键技能，并将受益于与来自不同领域的知名研究人员的频繁互动，团队成员将通过开发个性化的研究项目来参与实践本科教育和培训，从而获得荣誉论文、在国家会议上的演讲和演讲。研究生和本科生还将参加 K-12 科学推广活动，帮助吸引下一代海洋学家并为他们提供信息。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，并直接参与北卡罗来纳州科学节。通过 TED 演讲与媒体联系，令人兴奋的结果将广泛传播给公众，该项目将直接关系到理解微生物介导的对东南大西洋边缘意外释放的碳氢化合物的反应，那里的石油和天然气勘探是国家的一个持续话题。最近在北卡罗来纳州哈特拉斯角近海发现的数百个天然气渗漏点以及墨西哥湾北部的数千个天然气渗漏点，通过上升的溶解作用将大量溶解的甲烷注入上覆陆架和斜坡水域。甲烷的命运很大程度上取决于微生物氧化和远离渗流源的平流输送之间的平衡，微生物氧化的功效可能取决于甲烷、氧气和环境溶解无机氮 (DIN) 以及溶解的无机氮 (DIN) 的浓度。最近的船上有氧甲烷氧化率（AMOR）测量表明，微生物对渗流甲烷的消耗可能会滞后一周，因此物理分散可以通过稀释来控制深水甲烷动力学。然而，底层水中的甲烷稳定碳同位素测量表明，在注入甲烷的剧烈氧化开始之前不存在滞后，同时研究其微生物驱动因素。北卡罗来纳州和墨西哥湾大陆边缘的代表性地点具有大量活跃的气泡渗漏，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的大部分不确定性。我们将利用新开发的底栖着陆器系统进行测量，该系统配备先进的激光甲烷传感器，能够进行数周的 AMOR 测量，同时分析溶解氧、DIN 和微生物群落是否存在甲烷氧化菌（通过宏基因组）及其活性。 （通过元转录组）可以揭示甲烷营养对环境甲烷浓度的反应的本质。该项目将测试有关深海甲烷动力学的关键假设，包括确定是否存在显着的滞后暴露于升高的甲烷浓度后的微生物反应，确定 AMOR 与甲烷和 DIN 浓度的关系，并研究甲烷氧化菌对甲烷浓度时空变化的响应时间和幅度，将成功收集原位 AMOR 和相关微生物群落数据。事实证明，对于在一系列海洋条件下模拟海洋甲烷动力学非常重要，包括富含渗流的底层水和意外碳氢化合物释放。该奖项反映了 NSF 的法定使命，并通过评估被认为值得支持利用基金会的智力优势和更广泛的影响审查标准。