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Thread: New estimates of large methane flux from Siberian sediments

  1. #1 New estimates of large methane flux from Siberian sediments 
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    The current issue of Science has some rather remarkable estimates of potential ongoing methane release from warming arctic waters.

    Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere. The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate.
    http://www.sciencemag.org/cgi/conten.../327/5970/1246

    This is in fact an Earth Science topic, but may become a climate thread.


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    Forum Isotope Bunbury's Avatar
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    I find this a bit confusing. The RealClimate article about this paper that appeared a few days ago seemed to downplay the significance of the ESAS methane releases with respect to climate warming, on the bases that a) most methane release to the atmosphere comes from land sources (natural and rice paddies), the sea's contribution being quite small by comparison ; b) the ESAS measurements are a snapshot with no way to know if the rate of release has actually changed; c) methane oxidizes to CO2 in the atmosphere so its very high GWP is short lived (not to ignore the CO2 that results).

    The comments following the RC article were generally of the sense that "oh, well that's OK then, no need to worry about this." I wonder if this isn't being a bit complacent. But I also wonder if these observations are really meaningful especially considering point b) above, or is there a benchmark that these observations can be compared to?


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  4. #3 Re: New estimates of large methane flux from Siberian sedime 
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    Quote Originally Posted by free radical
    The current issue of Science has some rather remarkable estimates of potential ongoing methane release from warming arctic waters.

    Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere. The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate.
    http://www.sciencemag.org/cgi/conten.../327/5970/1246

    This is in fact an Earth Science topic, but may become a climate thread.
    Methane is a concern. I have meant to look at and graph and quantify the last few decades of its radiative effect, but haven't yet. I think it may be the warming since the 80's issue. Small changes in CH4 can still make large temperature changes.

    Now an I to understand that this will be CH4 lagging temperature?
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  5. #4  
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    Quote Originally Posted by Bunbury
    I find this a bit confusing. The RealClimate article about this paper that appeared a few days ago seemed to downplay the significance of the ESAS methane releases with respect to climate warming, on the bases that a) most methane release to the atmosphere comes from land sources (natural and rice paddies), the sea's contribution being quite small by comparison ; b) the ESAS measurements are a snapshot with no way to know if the rate of release has actually changed; c) methane oxidizes to CO2 in the atmosphere so its very high GWP is short lived (not to ignore the CO2 that results).

    The comments following the RC article were generally of the sense that "oh, well that's OK then, no need to worry about this." I wonder if this isn't being a bit complacent. But I also wonder if these observations are really meaningful especially considering point b) above, or is there a benchmark that these observations can be compared to?
    I don't know what to make of it yet myself. Since I don't have access to the full article, do they attempt to quantify the change in atmospheric CH4? If we assume the radiative forcing of CH4 in the IPCC AR4 is correct, then my assessment says that an increase to about 2500 ppb would have a radiative forcing increase of 0.24 watts above the 2005 levels, or half again as much as 1750 to 2005 levels.
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    Quote Originally Posted by Bunbury
    I find this a bit confusing. The RealClimate article about this paper that appeared a few days ago seemed to downplay the significance of the ESAS methane releases with respect to climate warming, on the bases that a) most methane release to the atmosphere comes from land sources (natural and rice paddies), the sea's contribution being quite small by comparison ; b) the ESAS measurements are a snapshot with no way to know if the rate of release has actually changed; c) methane oxidizes to CO2 in the atmosphere so its very high GWP is short lived (not to ignore the CO2 that results).

    The comments following the RC article were generally of the sense that "oh, well that's OK then, no need to worry about this." I wonder if this isn't being a bit complacent. But I also wonder if these observations are really meaningful especially considering point b) above, or is there a benchmark that these observations can be compared to?
    Yes, I agree generally with your comments. My understanding is that the supersaturation of methane was unexpected, and warranted publication, particularly in light of concerns that sudden clathrate 'melt' could potentially contribute to increased rates of warming.

    Whether supersaturation of methane in surface waters (ie available to release to the atmosphere) is common or not is somewhat controversial. Some areas of the ocean's surface do seem to be super-saturated with methane, but typically does not appear to be related to a deep source. In this case, it appears that the ocean's water column may not be filtering the methane as it transits to the surface, which is a reasonable cause for some concern, though not alarm.
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    Some areas of the ocean's surface do seem to be super-saturated with methane, but typically does not appear to be related to a deep source.
    So associated with biological activity?
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    It is not known, transport from shelf sediments is possible, or other physical methods of transportation. I know of no abiotic processes of methane formation that are relevant in surface waters. Biological processes are likely, though methanogens are typicall anaerobic, thus unlikely to be common in surface waters. Other methane forming pathways have been describe among Enterobacteriaceae, which may contribute to methane in surface waters.
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