The above image shows that, over a period of less than two days, huge amounts of methane show up over the depth of the Arctic Ocean, especially along the fault line that crosses the Arctic Ocean and extends into Siberia and further into the Sea of Okhotsk. On October 17, 2013, readings of up to 2351 ppb were recorded.
The above image shows that such high readings have occurred before over the past few months. This time, however, this high reading can be more clearly attributed to methane escaping from the depth of the Arctic Ocean, as also indicated by the image below that shows that at 469 mb (i.e. the altitude at which this high reading was recorded on the afternoon of October 17) methane was predominantly present at higher northern latitudes.
The methane that appears over the depth of the Arctic Ocean is likely have traveled a long path through the vertical water column before entering the atmosphere. Clearly, some of the methane must have oxidized in the ocean. Therefore, methane must be escaping from the seabed in amounts far higher than what is visible in the air.
Below follows some history regarding this unfolding methane catastrophe. Note that methane concentrations in the water are measured in nM, while methane concentrations in the atmosphere are typically measured in parts per billion (ppb).
There are vast amounts of methane in sediments underneath the Arctic Ocean. Natalia Shakhova et al. (2010) estimate the accumulated potential for the East Siberian Arctic Shelf (ESAS) region alone (image on the right) as follows:
- organic carbon in permafrost of about 500 Gt
- about 1000 Gt in hydrate deposits
- about 700 Gt in free gas beneath the gas hydrate stability zone.8
The danger that volcanic and earthquake activity along the Gakkel Ridge could lead to destabilization and abrupt methane release into the atmosphere was highlighted by Light and Sorana back in 2002.1
Measurements taken in September 2003 and September 2004 show that the surface layer of shelf water in the East-Siberian Sea and Laptev Sea was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water suggest that the bottom layer is somehow affected by near-bottom sources. Considering the possible formation mechanisms of such plumes, we favor thermo-abrasion and the effects of shallow gas or gas hydrates release, conclude the authors of this study, published in 2005.2
The authors conclude: "Since the area of geological disjunctives (fault zones, tectonically and seismically active areas) within the Siberian Arctic shelf composes not less than 1-2% of the total area and area of open taliks (area of melt through permafrost), acting as a pathway for methane escape within the Siberian Arctic shelf reaches up to 5-10% of the total area, we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause ∼12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming".3
In 2007, concentrations of dissolved methane in the water column reached a level of over 5141 nM at a location in the Laptev Sea.4
A study published in 2008 found volcanoes up to 2,000 m in diameter and a few hundred metres high at the bottom of the Arctic Ocean, at Gakkel Ridge.5
End September 2011, a cluster of methane plumes, over one km in diameter, appeared in the Laptev Sea, as shown on the image below, from a paper on the unfolding "Methane Catastrophe".6
1. Arctic Methane Hydrates: A Potential Greenhouse Gas Hazard. - Light, M.P.R. and Solana, C. (2002)
For more details, see also
2. The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle. - Natalia Shakhova, Igor Semiletov and Gleb Panteleev (2005)
3. Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates? - N. Shakhova, I. Semiletov, A. Salyuk and D. Kosmach (2008)
4. Siberian Sea Shelf Study, International Arctic Research Center, University of Alaska Fairbanks
5. Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean. - Sohn RA et al. (2008)
6. The Degradation of Submarine Permafrost and the Destruction of Hydrates on the Shelf of East Arctic Seas as a Potential Cause of the “Methane Catastrophe”: Some Results of Integrated Studies in 2011. - V. I. Sergienko et al., in Oceanology (Sept. 2012)
7. On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere system. - Semiletov et al. (2012)
8. Methane release from the East Siberian Arctic Shelf and the Potential for Abrupt Climate Change. - Natalia Shakhova and Igor Semiletov (2010), Presentation at Symposium, November 30, 2010
9. High Methane Readings continue over Depth of Arctic Ocean