Mechanics of methane bubbles in consolidated aquatic muds

IF 10.8 1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
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Abstract

Methane (CH4) is a potent greenhouse gas that has a major impact on Earth's climate. CH4 is accommodated in discrete bubbles in aquatic muds, whose sizes greatly exceed the pore size of the hosting sediment. This critical review examines the mechanics of CH4 gas in consolidated aquatic muds at the scale of a single bubble and at a macroscale of gassy sediments, obtained from lab experiments, field observations, and numerical and analytical modeling. Linear elastic fracture mechanics (LEFM) theory is shown to control the single bubble shape, size, morphology, and inner pressure evolution over its entire life cycle. Reviewed implications focus on the effects of the inner bubble pressure on its solute exchange with ambient pore waters; on the dynamic water load effect (e.g., waves, tides) on the bubble growth rate and its release from sediment into the water column; and on competitive bubble pair growth in the aquatic muds, the process that presumably shapes the bubble size distribution pattern in muds. Alternatively, gassy sediment effective mechanical and physical characteristics and effective gassy media theories are examined at the macroscale, which makes them suitable for remote sensing acoustic applications. This review indicates, however, that most of the developed macroscale effective medium theories rely on the cumulative sediment gas content. Moreover, no theory for proper upscaling of the entire set of the microscale single bubble descriptors addressed in this review – bubble size distribution, their orientations and spatial locations, and inner bubble pressures – to the effective medium mechanical properties of gassy muds, exists. This review will serve, therefore, as a basis for the improved upscaling, while preserving the basic microscale bubble descriptors, their growth physics, and controls. Laying this foundation will enhance the accuracy of the acoustic applications. Improved assessment of sediment gas retention based on this upscaling will contribute to geohazard prediction and should reduce a long-persisting uncertainty related to CH4 fluxes from the aquatic sediments.

固结水生淤泥中甲烷气泡的力学原理
甲烷(CH4)是一种对地球气候有重大影响的强效温室气体。CH4 存在于水生淤泥中的离散气泡中,其大小大大超过了所在沉积物的孔径。本评论通过实验室实验、实地观测以及数值和分析建模,从单个气泡尺度和含气沉积物的宏观尺度研究了CH4气体在固结水生泥浆中的力学作用。研究表明,线性弹性断裂力学(LEFM)理论可以控制单个气泡的形状、大小、形态和整个生命周期的内压演变。研究的意义主要集中在气泡内压对其与周围孔隙水进行溶质交换的影响;动态水负荷(如海浪、潮汐)对气泡生长速度及其从沉积物中释放到水体的影响;以及水生淤泥中气泡成对竞争生长的影响,这一过程可能塑造了淤泥中气泡的大小分布模式。此外,还在宏观尺度上研究了含气沉积物的有效机械和物理特性以及有效含气介质理论,这使它们适合于遥感声学应用。然而,本综述表明,大多数已开发的宏观有效介质理论都依赖于累积沉积物气体含量。此外,本综述中涉及的一整套微观单一气泡描述指标--气泡大小分布、其方向和空间位置以及内部气泡压力--都没有理论可以适当地提升到含气泥浆的有效介质机械特性。因此,本综述将作为改进升级的基础,同时保留基本的微尺度气泡描述符、其生长物理和控制。奠定这一基础将提高声学应用的准确性。在此基础上改进的沉积物气体滞留评估将有助于地质灾害预测,并应减少与水生沉积物 CH4 通量有关的长期存在的不确定性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Earth-Science Reviews
Earth-Science Reviews 地学-地球科学综合
CiteScore
21.70
自引率
5.80%
发文量
294
审稿时长
15.1 weeks
期刊介绍: Covering a much wider field than the usual specialist journals, Earth Science Reviews publishes review articles dealing with all aspects of Earth Sciences, and is an important vehicle for allowing readers to see their particular interest related to the Earth Sciences as a whole.
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