Scientists use sophisticated microphones to listen to the ocean pass gas

Methane bubbles being expelled from the sea floor.

From OREGON STATE UNIVERSITY and the “there’s a joke in there somewhere” department comes this report on ocean reports.

Scientists use hydrophone to listen in on methane seeps in ocean

NEWPORT, Ore. – A research team has successfully recorded the sound of methane bubbles from the seafloor off the Oregon coast using a hydrophone, opening the door to using acoustics to identify – and perhaps quantify – this important greenhouse gas in the ocean.

The next step, researchers say, is to fine-tune their ability to detect the acoustic signature of the bubbles so they can use the sounds to estimate the volume of methane in the offshore reservoirs.

Results of the study have just been published in the journal Deep-Sea Research II.

“The bubbles in the streams make sound, and the frequency of the sound is related to the size of the bubble,” said Robert Dziak, an acoustics scientist with the National Oceanic and Atmospheric Administration and lead author on the study. “The smaller the bubble, the higher the pitch. And the larger the bubble, the lower the sound pitch, but the more methane it contains.

“Our ultimate goal is to use sound to estimate the volume and rate of methane gas exiting these seafloor fields,” added Dziak, who has a courtesy appointment in OSU’s College of Earth, Ocean, and Atmospheric Sciences.

In recent years, scientists have found hundreds of bubble streams emanating from methane deposits off the Pacific Northwest coast, but they have no way to determine how much methane is stored there. Methane is found both as an icy hydrate deposit and in a gas phase within the sediments of the continental margins.

It potentially could be a new energy source, or it could pose a serious environmental threat as a greenhouse gas.

The research team used the remotely operated vehicle (ROV) Hercules from the Exploration Vessel (E/V) Nautilus, owned and operated by the Ocean Exploration Trust, to deploy a hydrophone about 10 kilometers off Heceta Bank on the Oregon continental margin in 1,228 meters of water (about three-fourths of a mile deep). The acoustic signatures of the bubbles from the seep site are depicted in the hydrophone record as a series of short, high-frequency bursts, lasting 2-3 seconds.

The researchers then compared the sound record with still images from the ROV and found their estimates of bubble size from the hydrophone record matched the visual evidence.

This June, a project led by OSU researchers Tamara Baumberger and Susan Merle and utilizing the E/V Nautilus will map additional methane seep sites off the Pacific Northwest coast. Dziak and OSU researcher Haru Matsumoto will work with the team to deploy a hydrophone into the depths of Astoria Canyon at the site of a high-rate methane seep and leave it there for 2-3 days.

The expedition will feature a live, 24/7 broadcast on http://www.nautiluslive.org.

“The frequencies are so high on some of these recordings that the data drive fills up quickly on battery-operated hydrophones,” Dziak said. “However, this new experiment will record for a longer time period, allowing us to see how seafloor methane emissions vary over time, and how they may be influenced by the ocean tides.”

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The paper: https://www.sciencedirect.com/science/article/pii/S096706451730084X?via%3Dihub

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16 thoughts on “Scientists use sophisticated microphones to listen to the ocean pass gas

  1. Before drilling in the shallow Gulf Of Mexico operators were required to conduct site hazard surveys. This included side scanning sonar profiles to locate wrecks, paleo indian mounds and other places to not plant a jackup’s mat. Shallow gas charged sands are a hazard, because they can blow out before the drill hole is cased. One could see curtains of gas bubbles seeping from the sea floor where shallow faults outcropped. Also, pot holes were commonly seen as sites for older gas seeps.

    So, I guess there is nothing new here, including the researchers’ abysmal ignorance of remotes sensing techniques in shallow waters. Please send money, And snacks.

    Tom Bakewell

    • This is really good as once I researched the literature on bubbles because fish make bubbles, and waves make bubbles, among other phenomena. This was probably a serious problem to Arrhenius and his cohorts. The ocean is a noisy place and with improved technology there is a fair amount of research trying to measure fish concentrations around oil platforms and other places where the turbidity makes counting difficult and sampling and modeling populations is not good.

      Try these.
      Blanchard, D. C. 1963. The electrification of the atmosphere by particles from bubbles in the sea. pp. 71-202 In, Sears, M. (Ed.) Progress in Oceanography I. Macmillan, NY.
      Fox, F. E. and K. F. Herzfeld. 1954. Gas bubbles with organic skin as cavitation nuclei. Journal Acoustical Society America. 26(6):984-989.
      Graham, A. and A. J. Hall. 1997. The horizontal distribution of bubbles in a shallow sea. Continental Shelf Research. 17(9):1051-1082.
      And so on, carbon dioxide processes make bubbles, and as noted natural oil leaks make bubbles.

  2. If the water is that deep, I wonder how much of the methane reaches the surface uneaten by microrganisms? There are a fair number of wee beasties that metabolize CH4.

    • In addition …

      “Methane released from the seafloor and transported to the atmosphere has the potential to amplify global warming. At an arctic site characterized by high methane flux from the seafloor, we measured methane and carbon dioxide (CO2) exchange across the sea−air interface. We found that CO2 uptake in an area of elevated methane efflux was enhanced relative to surrounding waters, such that the negative radiative forcing effect (cooling) resulting from CO2 uptake overwhelmed the positive radiative forcing effect (warming) supported by methane output. Our work suggests physical mechanisms (e.g., upwelling) that transport methane to the surface may also transport nutrient-enriched water that supports enhanced primary production and CO2 drawdown. These areas of methane seepage may be net greenhouse gas sinks.”

      Source: http://www.pnas.org/content/114/21/5355

  3. “It potentially could be a new energy source, or it could pose a serious environmental threat as a greenhouse gas.” Don’t you think this methane has been escaping from the bottom of the oceans since time immoral. Unless it can be proved that it has gotten worse recently, this greenhouse gas is already baked into the affect it has on earth’s climate. Nice to think about but does it really matter?

    • SF author John Barnes wrote “Mother of Storms”, where a military incident released huge quantities of methane from Arctic clathrates. The result – a ginormous (and permanent) hurricane! See! Greenhouse gas at work!
      Great fiction – not so sure about the science…

  4. “… Dziak, who has a courtesy appointment …” What is a “courtesy appointment”?

    “The smaller the bubble, the higher the pitch. And the larger the bubble, the lower the sound pitch, but the more methane it contains.” The bubbles emerge from the seafloor, where the ocean is at higher pressure than the surface. They then rise toward the surface, into water at lower pressure. Wouldn’t a bubble naturally expand as it rises, yet contain the same amount of methane as when it vented from the sea floor? Or is this just poorly written?

    “… to fine-tune their ability to detect the acoustic signature of the bubbles so they can use the sounds to estimate the volume of methane in the offshore reservoirs.” How can determining how many bubbles are seeping out of the sea floor going to help estimate the size of the reservoir?

  5. How are they going to acoustically determine if the bubbles are entirely methane? The Pine Island Glacier article earlier today says helium-3 is emitted from the mantle and I imagine other gases as well.

  6. A Holter monitor is a small, battery-powered medical device that measures your heart’s activity, . . .
    A Baumberger/Merle monitor is a small, battery-powered medical device that measures your intestinal activity, thereby estimating your conversion of food types into green house gasses. These may become mandatory during the next US Democratic Administration. Once a tipping point has been established, you will be shut down (aka disappeared) when that number is exceeded.

  7. As any bread baker can tell you, the size of the bubble alone does not indicate the amount of gas. Two identical doughs, handled differently, will have differently sized alveoli.

    The purpose of punching down is usually to break up the bubbles into smaller ones, not expel the gas. Many bakers prefer large holes in the crumb, so handle the dough gently. Others, say those making sandwich loaves, want small holes to keep the jelly on the bread instead of their shirt front, so are more energetic. Either way, the volume will be the same.

    The bubbles’ size will not tell you anything, by itself, about how much gas went into those bubbles. How fast are they expelled? What is the size of the vent? Is it continuous? Does it percolate à la “Old Faithful”? Maybe they should hire an ex-navy sonar man before they make fools of themselves.

  8. Odd, no mention about distinguishing between methane seeps and the bubble screens used by dolphins, orcas and whales…

    Must be methane they’re using.

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