August 19, 2009

Methane Escaping From The Arctic Sea Floor

A research team is claiming to have evidence that shows methane is escaping from the Arctic sea bed.

The team, which conducted research from the sea bed off Norway, found more than 250 plumes of methane bubbles rising from the sea floor.

As temperatures in the region rise, the sea bed grows warmer, allowing frozen water crystals to break down and release methane.

According to the team's report, which appears in Geophysical Research Letters, detected the bubbles using sonar and tested for methane at depths between 150 and 400 meters.

The powerful greenhouse gas is normally trapped in sediment under the ocean floor as a "methane hydrate," which is an ice-like substance composed of water and methane.

"Methane hydrate" is stable under conditions of high pressure and low temperature, but breaks down as temperatures rise.

Currently, the methane is stable at depths lower than 400m.  Previous data showed that the gas was stable at depths below 360m.

Records also show that the ocean temperature in the region has warmed by 1C over the past 30 years.

The research, which was carried out as part of the International Polar Year Initiative and funded by Britain's Natural Environment Research Council (NERC), is the first example of the loss of stability during a geological period due to temperature rise.

"We already knew there was some methane hydrate in the ocean off Spitsbergen and that's an area where climate change is happening rather faster than just about anywhere else in the world," Professor Tim Minshull of the National Oceanography Center told BBC News.

"There's been an idea for a long time that if the oceans warm, methane might be released from hydrate beneath the sea floor and generate a positive greenhouse effect. What we're trying to do is to use lots of different techniques to assess whether this was something that was likely to happen in a relatively short time scale off Spitsbergen," he added.

The researchers do believe that some form of methane release has been going on in the region since the last ice age.

The findings do associate climate change with the depths at which methane is being released in the ocean.

"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," Professor Minshull said.

"We were slightly surprised that if there was so much methane rising why no one had seen it before. But I think the reason is that you have to be rather dedicated to spot it because these plumes are only perhaps 50m to 100m across."

"The device we were using is only switched on during biological cruises. It's not normally used on geophysical or oceanographic cruises like ours. And of course you've got to monitor it 24 hours a day. In fact, we only spotted the phenomenon half way through our cruise. We decided to go back and take a closer look."

The researchers also noted that the majority of the released methane never reached the surface.

This does not mean that the gas is not entering the atmosphere, the team stressed. 

Currently, the methane seeps are unpredictable, and there is a possibility of larger seeps breaking the surface in other areas.

According to the researchers, the methane reacts with oxygen in the sea water to form carbonic acid which contributes to ocean acidification, another problem associated with climate change.

"If this process becomes widespread along Arctic continental margins, tens of megatons of methane a year - equivalent to 5-10% of the total amount released globally by natural sources, could be released into the ocean," said Graham Westbrook, lead author of the study.

The researchers plan to study the behavior of the plumes during an expedition next year.


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