Supersaturated Siberian Seas

Winter ice

19th April 2010.

Covered in ice for 265 days of the year, and bordered by the frozen wastes of the Siberian tundra, it is hardly surprising that the shallow seas of East Siberian Arctic Shelf (ESAS) have not before now been subject to extensive monitoring for methane emissions.  However, due to the efforts of an international collaboration between researchers based in Alaska, Vladivostock and Stockholm, a comprehensive survey of methane concentrations in these waters has now been conducted.  The results, reported in Science (Shakhova et al. 2010) make compelling reading and raise new questions about future Arctic methane fluxes.

Six summer field campaigns were conducted between 2003 and 2008, and methane concentrations were measured in 5100 seawater samples taken from 1080 stations.  The researchers found that over 50% of the surface waters were supersaturated with methane. In hotspot areas, the median supersaturation was 8300%.  One over-ice winter expedition and one helicopter survey provided additional data with which to constrain estimates of the total methane flux from these Arctic seas.  Based on all the observations, the team calculated annual atmospheric methane flux from the ESAS at 7.98 Tg C-CH4. To put this in context, previous research has estimated the global methane flux from oceans as 4 – 15 Tg C-CH4 y-1 (IPCC, 2007).

The worldwide ocean methane flux figures would remain relatively small compared to terrestrial sources such as wetlands and rice paddies, even if revised upwards based on the ESAS study. The new data are however interesting  in that they demonstrate the potential for methane emissions from flooded areas underlain by large pools of carbon-rich vulnerable permafrost. The authors note that the question of whether the amount of methane being released from the ESAS sediments has changed in response to the general warming of the Arctic region is not answered by their study, and suggest that this issue merits further attention.

Natalia Shakhova, Igor Semiletov, Anatoly Salyuk, Vladimir Yusupov, Denis Kosmach, and Örjan Gustafsson. 2010. Science 1246-1250.