Investigations of Aerobic Methane Oxidation in Two Marine Seep Environments: Part 2-Isotopic Kinetics
Investigations of Aerobic Methane Oxidation in Two Marine Seep Environments: Part 2-Isotopic Kinetics
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DOI：
10.1029/2019jc015603
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发表时间：
2019-11-30
影响因子：
3.6
通讯作者：
Kessler, J. D.
中科院分区：
文献类型：
--
作者：
Chan, E. W.;Shiller, A. M.;Kessler, J. D.
在海水中甲烷（CH 4）的有氧氧化过程中，一个减轻大气排放的过程，C-12-同位素体以比C-13-同位素体稍大的速率常数反应，使残留的CH 4同位素分馏。先前的研究试图利用甲烷氧化的系统同位素分馏来量化甲烷池在海水中被氧化的程度。然而，基于培养的研究表明，同位素分馏从根本上改变作为一个微生物种群的反应性底物的涌入而大量繁殖。使用系统的围隔培养研究与最近收集的海水，在这里，我们调查的基本同位素动力学的好氧甲烷氧化过程中的微生物水华。正如配套文件中所详述的，海水样本是从美国大西洋边缘哈德逊峡谷的渗漏场和Woolsey Mound（也称为睡龙）顶部采集的，Woolsey Mound是墨西哥湾北方租赁区块MC 118的一部分，并用于这些调查。哈德逊峡谷和MC 118的研究结果表明，在这些自然环境中，甲烷氧化的同位素分馏遵循一级动力学过程。结果还表明，同位素分馏因子保持不变，在此甲烷营养水华一旦快速甲烷氧化开始，分馏因子的大小出现相关的一级反应速率常数。这些研究结果大大简化了使用天然稳定同位素的变化，甲烷在海底释放后，在海水中的甲烷被氧化的程度进行评估。
During aerobic oxidation of methane (CH4) in seawater, a process which mitigates atmospheric emissions, the C-12-isotopologue reacts with a slightly greater rate constant than the C-13-isotopologue, leaving the residual CH4 isotopically fractionated. Prior studies have attempted to exploit this systematic isotopic fractionation from methane oxidation to quantify the extent that a CH4 pool has been oxidized in seawater. However, cultivation-based studies have suggested that isotopic fractionation fundamentally changes as a microbial population blooms in response to an influx of reactive substrates. Using a systematic mesocosm incubation study with recently collected seawater, here we investigate the fundamental isotopic kinetics of aerobic CH4 oxidation during a microbial bloom. As detailed in a companion paper, seawater samples were collected from seep fields in Hudson Canyon, U.S. Atlantic Margin, and atop Woolsey Mound (also known as Sleeping Dragon) which is part of lease block MC118 in the northern Gulf of Mexico, and used in these investigations. The results from both Hudson Canyon and MC118 show that in these natural environments isotopic fraction for CH4 oxidation follows a first-order kinetic process. The results also show that the isotopic fractionation factor remains constant during this methanotrophic bloom once rapid CH4 oxidation begins and that the magnitude of the fractionation factor appears correlated with the first-order reaction rate constant. These findings greatly simplify the use of natural stable isotope changes in CH4 to assess the extent that CH4 is oxidized in seawater following seafloor release.