Article

Enhanced lifetime of methane bubble streams within the deep ocean. Geophys Res Lett

Monterey Bay Aquarium Research Institute, Moss Beach, California, United States
Geophysical Research Letters (Impact Factor: 4.2). 08/2002; 29(15). DOI: 10.1029/2001GL013966

ABSTRACT

1] We have made direct comparisons of the dissolution and rise rates of methane and argon bubbles experimentally released in the ocean at depths from 440 to 830 m. The bubbles were injected from the ROV Ventana into a box open at the top and the bottom, and imaged by HDTV while in free motion. The vehicle was piloted upwards at the rise rate of the bubbles. Methane and argon show closely similar behavior at depths above the methane hydrate stability field. Below that boundary ($520 m) markedly enhanced methane bubble lifetimes are observed, and are attribute to the formation of a hydrate skin. This effect greatly increases the ease with which methane gas released at depth, either by natural or industrial events, can penetrate the shallow ocean layers.

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Available from: Gregor Rehder, Jun 23, 2015
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    • "Releases of methane are often accompanied by hydrate shell formation and surfactants like oil, both strongly affecting the rise characteristics and fate of the bubbles (e.g. [7]–[9]). Furthermore oil coated bubbles are suggested to be able to transport the methane preferable to the oceans surface preventing them from dissolving underway [10]. "
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    • "The rapidity of this process strongly depends on the bubble size, the rise velocity, as well as the composition and conditions of the surrounding medium and the presence of upwelling flows (Leifer and Judd, 2002). Several studies have demonstrated that methane escapes the bubbles well before final bubble dissolution (Leifer and Patro, 2002; McGinnis et al., 2006; Rehder et al., 2002). Our suggestion that most of the methane discharged from the South Georgia northern shelf does not reach the upper water column is additionally strengthened by the relatively low concentrations of dissolved methane (about 5 nmol/l) in the intermediate to uppermost water masses at two hydrocast stations, deliberately acquired close to recorded flares in the Cumberland Bay area (Figs. "
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    ABSTRACT: An extensive submarine cold-seep area was discovered on the northern shelf of South Georgia during R/V Polarstern cruise ANT-XXIX/4 in spring 2013. Hydroacoustic surveys documented the presence of 133 gas bubble emissions, which were restricted to glacially-formed fjords and troughs. Video-based sea floor observations confirmed the sea floor origin of the gas emissions and spatially related microbial mats. Effective methane transport from these emissions into the hydrosphere was proven by relative enrichments of dissolved methane in near-bottom waters. Stable carbon isotopic signatures pointed to a predominant microbial methane formation, presumably based on high organic matter sedimentation in this region. Although known from many continental margins in the world's oceans, this is the first report of an active area of methane seepage in the Southern Ocean. Our finding of substantial methane emission related to a trough and fjord system, a topographical setting that exists commonly in glacially-affected areas, opens up the possibility that methane seepage is a more widespread phenomenon in polar and sub-polar regions than previously thought.
    Full-text · Article · Oct 2014 · Earth and Planetary Science Letters
    • "Releases of methane are often accompanied by hydrate shell formation and surfactants like oil, both strongly affecting the rise characteristics and fate of the bubbles (e.g. [7]–[9]). Furthermore oil coated bubbles are suggested to be able to transport the methane preferable to the oceans surface preventing them from dissolving underway [10]. "

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