Investigations of Aerobic Methane Oxidation in Two Marine Seep Environments: Part 1—Chemical Kinetics
Investigations of Aerobic Methane Oxidation in Two Marine Seep Environments: Part 1—Chemical Kinetics
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DOI：
10.1029/2019jc015594
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发表时间：
2019-11
影响因子：
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通讯作者：
E. Chan;A. Shiller;D. Joung;E. Arrington;D. Valentine;M. Redmond;J. Breier;S. Socolofsky;J. Kessler
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文献类型：
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作者：
E. Chan;A. Shiller;D. Joung;E. Arrington;D. Valentine;M. Redmond;J. Breier;S. Socolofsky;J. Kessler
众所周知，微生物好氧氧化是海洋甲烷(CH4)的一个重要汇，有助于在大片海洋上相对较小的大气排放这种温室气体。然而，甲烷好氧氧化的化学动力学尚未很好地建立，这使得预测和评估海底释放后甲烷在海水中的氧化程度变得困难。在这里，我们使用从美国大西洋边缘哈德逊峡谷和墨西哥湾MC118渗漏场采集的新鲜海水样品的中膜培养来研究甲烷好氧氧化的动力学，以获得对这个甲烷汇的基本化学了解。这项研究的目的是确定CH4释放到更快速氧化开始的反应或滞后时间、反应顺序以及在CH4氧化过程中使用的反应物(即CH4、氧气、硝酸盐、磷酸盐、微量金属)的化学计量比。对哈德逊峡谷和MC118环境的研究结果表明，在海水接种甲烷后不到一个月的时间里，甲烷的氧化速率急剧增加。然而，这种更快的CH4氧化的确切时间特征因位置而异，可能取决于海水收集点的局部环流和生物地球化学条件。数据进一步表明，甲烷氧化反应为一级动力学过程，一旦甲烷快速氧化开始，反应速率常数保持不变。简而言之，全球最大的甲烷储藏库位于海底及其下方，甲烷是一种强有力的温室气体。甲烷从海底释放后，很大一部分会溶解在上面的海水中，并被本土微生物氧化，有助于防止其在大气中释放。然而，这一过程发生的时间和化学要求尚未确定，因此很难预测和评估海底释放后甲烷氧化的效率。这项研究使用从美国大西洋边缘和墨西哥湾海底甲烷释放活跃地区收集的水，系统地测量了海水中与有氧甲烷氧化有关的化学变化。这些结果有助于我们更好地理解海水中甲烷通常可以被氧化的速度和数量。
Microbial aerobic oxidation is known to be a significant sink of marine methane (CH4), contributing to the relatively minor atmospheric release of this greenhouse gas over vast stretches of the ocean. However, the chemical kinetics of aerobic CH4 oxidation are not well established, making it difficult to predict and assess the extent that CH4 is oxidized in seawater following seafloor release. Here we investigate the kinetics of aerobic CH4 oxidation using mesocosm incubations of fresh seawater samples collected from seep fields in Hudson Canyon, U.S. Atlantic Margin and MC118, Gulf of Mexico to gain a fundamental chemical understanding of this CH4 sink. The goals of this investigation were to determine the response or lag time following CH4 release until more rapid oxidation begins, the reaction order, and the stoichiometry of reactants utilized (i.e., CH4, oxygen, nitrate, phosphate, trace metals) during CH4 oxidation. The results for both Hudson Canyon and MC118 environments show that CH4 oxidation rates sharply increased within less than one month following the CH4 inoculation of seawater. However, the exact temporal characteristics of this more rapid CH4 oxidation varied based on location, possibly dependent on the local circulation and biogeochemical conditions at the point of seawater collection. The data further suggest that methane oxidation behaves as a first‐order kinetic process and that the reaction rate constant remains constant once rapid CH4 oxidation begins. Plain Language Summary In and below the seafloor resides the largest global reservoir of methane, a potent greenhouse gas. Following the release of methane from the seafloor, a significant fraction dissolves in the overlying seawater and is oxidized by indigenous microorganisms, helping to prevent its atmospheric release. However, the timing and chemical requirements for this process to occur are not well established, making it difficult to predict and assess the efficiency of methane oxidation following seafloor release. This study systematically measured the chemical changes that are associated with aerobic methane oxidation in seawater using water collected from regions of active seafloor methane release along the U.S. Atlantic margin and the Gulf of Mexico. These results help to refine our understanding of how quickly and how much methane can typically be oxidized in seawater.