Methane is escaping from the Arctic sea-bed

Scientists say they have evidence that the powerful greenhouse gas methane is escaping from the Arctic sea-bed. As temperatures rise, the sea-bed grows warmer and frozen water crystals in the sediment break down, allowing methane trapped inside them to escape. The research team found that more than 250 plumes of methane bubbles are rising from the sea-bed off Norway. The joint British and German research team detected the bubbles using a type of sonar normally used to search for shoals of fish. Once detected, the bubbles were sampled and tested for methane at a range of depths. Writing in Geophysical Research Letters, the team says the methane was rising from an area of sea-bed off West Spitsbergen, from depths between 150m and 400m.The gas is normally trapped as "methane hydrate" in sediment under the ocean floor. Methane hydrates Methane gas is trapped inside a crystal structure of water-ice The gas is released when the ice melts, normally at 0C. At higher pressure, ie under the ocean, hydrates are stable at higher temperatures. "Methane hydrate" is an ice-like substance composed of water and methane which is stable under conditions of high pressure and low temperature. As temperatures rise, the hydrate breaks down. So this new evidence shows that methane is stable at water depths greater than 400m off Spitsbergen. However, data collected over 30 years shows it was then stable at water depths as shallow as 360m. Temperature records show that this area of the ocean has warmed by 1C during the same period. The research was carried out as part of the International Polar Year Initiative, funded by Britain's Natural Environment Research Council (Nerc). The team says this is the first time that this loss of stability associated with temperature rise has been observed during the current geological period. Infographic (BBC) 1. Methane hydrate is stable below 400m 2. Nearer the surface the hydrate breaks down as temperatures rise and the methane is released 3. Gas rises from the sea-bed in plumes of bubbles - most of it dissolves before it reaches the surface 4. So far scientists haven't detected methane breaking the ocean surface - but they don't rule out the possibility http://news.bbc.co.uk/2/hi/science/nature/8205864.stm