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Ashwin Kumar

Dec 3, 2012
01:15

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Thanks for the proposal! 1) Is this proposal to strengthen downwelling where it already occurs (similar to the reference that is mentioned) or is it also to induce downwelling in stable waters that might be rich in methane? If the latter, how would destabilization of a stable water column be achieved? 2) Vertical mixing could raise temperatures of deeper waters and also contribute to triggering nucleation in otherwise supersaturated methane/water solutions. How would you rank these side effects with the benefits of oxygenation? 3)Are there other means to oxygenate deeper waters?

Andrew Lockley

Dec 3, 2012
07:41

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1) The reference is to the piping technology, and is not specific to its deployment in comparable flow conditions. Indeed, this approach would work better for methane in poorly mixed waters, where oxygen is not abundant. This is likely to be where there is limited downwelling, but may also be applied where there is a large nutrient flux to deep waters, leading to anoxia and methanogenesis. 2) If supersaturation is evident, the fountain depressurization technique is more suitable. In general, open water is unlikely to be lacking in nucleation points, as it will contain organic and inorganic suspended particles. 3) Aeration can be used to oxygenate deep waters, but bubbles create buoyant lift and will tend to displace methane laden waters towards the surface (the opposite of the desired effect). Additionally, overcoming buoyancy is energetically expensive. One point to consider is that the downwelled water should not contain large quantities of organic matter, which will tend to decompose. Finally, light can be used to oxygenate deep water by photosynthesis, but this is energetically impractical.

Michael Maccracken

May 3, 2013
03:06

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I don't understand the third response. Would not pumping down oxygenated waters lead to far more upward displacement of the methane containing waters that oxygenating the deeper waters with bubbles? And it would seem that pumping air down would be far less energy intensive than pumping water down while also likely increasing the change for an encounter between the oxygen and the methane. I would also think that there might be a link between this proposal and the one for lake sealing--that is, if one knows one has a lot of methane, why not try to capture it using surfactants? If that were what was desired then one would not want to pump down oxygen to oxidize the methane, but an essentially inert gas (N2, CO2, etc.) that would create bubbles into which the methane would dissolve and come to the surface to be captured by a surfactant that then allows capture of the methane.

Andrew Lockley

May 3, 2013
04:46

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Pumping air into deeper waters creates a body of water/air mix which is lighter than the surrounding water. Two effects then cause this body to rise. Firstly, the rising bubbles drag water along (microscale). Secondly, buoyancy effects cause the whole body of water to rise (mesoscale). Therefore, bubbles tend to make methane-rich water rise. This effect is negated once the bubbles have dissolved, but this may not happen until methane-rich water has been lifted to the surface, and can then diffuse its contents into the atmosphere. In extreme cases, it may be that supersaturated water is so lifted, causing a catastrophic and self-sustaining ebullition event. This would release large volumes of formerly dissolved gas to the atmosphere, and could result in an asphyxiating cloud of gas. Furthermore, the density changes would sink surface ships in the area, and the gas mix would extinguish aircraft engines. Such gas releases have been speculated as a cause for the alleged 'Bermuda triangle' losses. Conversely, oxygen rich water is neutrally buoyant. It therefore exerts only chemical and temperature effects, and does not cause column movement (unless temperature or salinity differences are substantial). Therefore, it is generally a safer mixing strategy - albeit one requiring larger mass movements. As regards the energy requirements, forcing air to depth requires energy input as work is being done. With neutrally-buoyant water, overcoming fluid friction is the only work. It is not impossible to imagine using an unreactive gas to extract the methane by diffusion into bubbles. However, the resulting gas stream would be well mixed, and therefore hard to process. It would seem easier to rely on biology, and simply ensure that there is enough oxygen at depth to allow methane metabolism.

2013geoengineeringjudges 2013geoengineeringjudges

Jul 10, 2013
01:18

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Thank you for sharing your ideas and for the work invested to create this proposal. Your proposal has been considered carefully by the judges, and while the proposal has interesting ideas, and we appreciate the response to questions that were raised, it is unclear where the right conditions (physical, chemical and biological) exist for this to work, and whether as a result the potential for the application of this scheme is large. While you raise the right questions in your proposal, answers to these are required for the proposal to be compelling.