Natalia Shakhova (et al) has published convincing evidence of methane venting from the Arctic continental shelf off northeastern Siberia (Laptev and East Siberian Sea), based on painstaking repeated surveys since 2003. In this region, the relatively shallow continental shelf extends up to 1000 kilometres north of the coastline. The seabed consists of relict permafrost from the last glaciation, when sea levels were considerably lower than today. The permafrost layer is assumed to contain substantial amounts of organic carbon; it also traps methane seeping up from underneath. In the permafrost, the methane forms relatively stable methane hydrates, but warming of the seawater will destabilize the hydrates, releasing methane into the sea waters.
The Russian team has found large areas with surface waters highly super saturated in methane; in some places, methane concentrations are more than 100 times higher than expected in equilibrium with the ambient atmosphere. Based on their extensive data set, team members estimate an annual outgassing to the atmosphere of ~8 × 10 grams of carbon (8 Tg C) as methane from the ESAS waters. Consistent with this, concurrent atmospheric concentration measurements on the ship and with a helicopter documented methane levels up to four times higher than recorded elsewhere in the Arctic basin.
Dr. Shakhova feels that a very small disturbance of gas hydrates could cause catastrophic consequences within a few decades. Shallow bottom sediment and underlying permafrost have warmed approximately 15°C since the time they originated. The implications of this trend are that shallow off-shore gas hydrate deposits could become vulnerable (Fig.2). She also notes that methane plumes found in the East-Siberian Sea (ESS) during the 1 st and 2nd Russian-U.S. joint cruises during September of 2003 and 2004 may indicate decaying gas hydrates in thawing undersea permafrost.