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.
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):
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