Scientists at the National Oceanography Centre, Southampton, UK, have found that the warming of an Arctic current over the last 30 years has triggered the release of methane - a potent greenhouse gas - from methane hydrate stored in the sediment beneath the seabed.

The scientists, working in collaboration with researchers from the University of Birmingham, Royal Holloway London, and IFM-Geomar in Germany have found that more than 250 plumes of bubbles of methane gas are rising from the seabed of the West Spitsbergen continental margin in the Arctic, in a depth range of 150 to 400 meters.

Methane released from gas hydrate in submarine sediments has been identified in the past as an agent of climate change, and the likelihood of methane being released in this way has been widely predicted.

Professor Tim Minshull, Head of the University of Southampton’s School of Ocean and Earth Science, explained, “Our survey was designed to work out how much methane might be released by future ocean warming; we did not expect to discover such strong evidence that this process has already started.”

The data were collected from the royal research ship RRS James Clark Ross, and the bubble plumes were detected using sonar and then sampled with a water-bottle sampling system over a range of depths. The results indicate that the warming of the northward-flowing West Spitsbergen current by 1° over the last thirty years has caused the release of methane, by breaking down methane hydrate in the sediment beneath the seabed.

Methane hydrate is an ice-like substance composed of water and methane, which is stable in conditions of high pressure and low temperature. Currently, methane hydrate is stable at water depths greater than 400 meters in the ocean off Spitsbergen. However, thirty years ago it was stable at water depths as shallow as 360 meters.

While most of the methane currently released from the seabed is dissolved in the seawater before it reaches the atmosphere, methane seeps are episodic and unpredictable. Periods of more vigorous outflow of methane into the atmosphere are possible.

The team is carrying out further investigations of the plumes, concentrating on observing the behavior of these gas seeps over time.

(National Oceanography Centre, Southampton)