Move over cows! Methane outgassing in the Arctic Sea

Methane!  Move over cow flatulence and burping, methane is leaking from under the Arctic in a big way.  Methane, that innocuous-seeming molecule with 4 hydrogens and a carbon, is actually a more potent greenhouse gas than the carbon dioxide molecule of greater fame–up to 25 times more potent actually.  However, atmospheric methane concentrations are much lower than atmospheric carbon dioxide concentrations….if you take a look at the graphs below, you see that CO2 concentrations are represented in parts per million, whereas methane concentrations are represented in parts per billion.

Atmospheric concentrations for major greenhouse gases. NOAA Earth Systems Research Laboratory

However, its high potential for radiative forcing makes methane a greenhouse gas to watch; and large fluxes of methane have been implicated in past climate shifts.  Today, the Arctic is warming faster than predicted, thus speeding the thawing of permafrost there, which contain huge stores of both carbon and methane.  A study recently published in Science (Shakhova et al. 2010) looked into methane fluxes in the East Siberian Arctic Sea (ESAS).  Most previous methane observations in the Arctic have involved terrestrial sources, rather than sub-sea ones–surprising, because the sub-sea permafrost at ESAS is exposed to annual average temperatures that are about 12-17 C warmer than nearby terrestrial permafrost, making it more vulnerable to thawing.  Observations from 100 stations show methane supersaturation in the water column, from 880-8300%.  Methane concentrations tended to be higher in the winter, due to the increased solubility of gases in colder seawater (this is how the global solubility pump works as well).  A combination of diffusion and ebullition (in this case, the release of large bubbles entrapped in annual sea ice) outgassing mechanisms were observed, with the total methane flux calculated to be approximately 7.98 teragrams C-CH4 annually, a number that is on par with the estimated total methane emissions from the global ocean.  If you’re not up to date on your really, really big number terminology, a teragram (Tg) is 1012 grams, which is roughly 3 times the mass of the Empire State building (thanks, Wolfram Alpha!).  That’s 1 Tg.  The authors report nearly 8 Tg outgassed annually from the ESAS.  Nevertheless, the authors warn that this observation should not hugely alter the world’s methane budget, but does indicate that methane is being released from sub-sea sedimentary sources in the Arctic. In other words, the permafrost here isn’t as permanent as was previously thought.  Could this be the beginnings of a massive methane venting event that could trigger climatic consequences?  We shall see.

Below is the lead author of this study, Dr. Natalia Shakhova, discussing these findings in detail (via YouTube).

 

 

 

Catch that this concentration of methane over the Arctic is the highest in the last 400, 000 years?  Whoa.

 

 

Reference (and those cited therein):

ResearchBlogging.org
Shakhova, N., Semiletov, I., Salyuk, A., Yusupov, V., Kosmach, D., & Gustafsson, O. (2010). Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf Science, 327 (5970), 1246-1250 DOI: 10.1126/science.1182221

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2 thoughts on “Move over cows! Methane outgassing in the Arctic Sea

  1. Or maybe the ocean bottom is doing what it has always been doing. We don’t know, as this is the first time they looked at the gas there. They’re comparing what they measured against estimates made before someone measured what they’ve measured.

    I estimate that New York City will be under five feet of water next month, although I haven’t gone there to measure anything.

    • Hi John. You’re absolutely correct; this should be taken as a new observation, not necessarily a new venting mechanism. We can’t really tell because we don’t have any true baseline data for this type of event. What I was trying to bring attention to was simply the observation of, and sheer magnitude of this methane source. Something like this in the Arctic was unheard of before this work and I believe that it’s important to highlight that. The climatic implications of massive methane venting are very real. If this is new, then it may be indicative of a larger event to come. If it’s been going on for ages, it’s still likely been affecting the climate and further understanding of this venting of an important radiative forcing gas will lead to further research. Anyway, with the rapidly warming Arctic, it is concievable that the permafrost thawing may be speeding up, which would likely affect release rates here. Also note that the authors of this study do not ascribe anthropogenic or natural causes.

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