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Arctic warming triggering methane release, study reveals

Rising temperatures in the Arctic are triggering the release of methane from the seabed, according to new research by German and British scientists published in the journal Geophysical Research Letters. During a research cruise in autumn 2008, the team discovered over 250 plu...

Rising temperatures in the Arctic are triggering the release of methane from the seabed, according to new research by German and British scientists published in the journal Geophysical Research Letters. During a research cruise in autumn 2008, the team discovered over 250 plumes of methane gas bubbling up from the seabed at depths of less than 400 metres off the coast of the Norwegian island Spitsbergen in the Arctic Ocean. The extent of the plumes came as a surprise to the researchers. '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,' commented Professor Tim Minshull of the National Oceanography Centre at the University of Southampton in the UK. The methane is released from methane hydrates found in marine sediments on the sea floor. Methane hydrate is an ice-like substance made up of water and methane that is stable at high pressures and low temperatures. Researchers have predicted for some time that as ocean temperatures rise, methane will be released as methane hydrates become unstable at ever greater depths. According to the researchers, 30 years ago methane hydrate was stable at depths of 360 metres. Today, it is only stable at depths of 400 metres. On board the research ship RRS James Clark Ross, the team used sonar to detect plumes of bubbles, then deployed a water-bottle sampling system to pick up bubble samples from different depths. In total they found over 250 plumes of methane at depths shallower than 400 metres; some plumes were even discovered in water shallower than 200 metres. The strength of the plumes varied widely; some of the plumes were so powerful that they came to within 50 metres of the water's surface before the gases dissolved into the water. The researchers believe that some plumes may be strong enough to release methane directly into the atmosphere on occasion. As well as contributing to climate change, dissolved methane makes the ocean more acidic and reduces the amount of oxygen dissolved in the water, making it a serious threat to much marine life. Over the past 30 years, the temperature of the stretch of ocean covered by this study rose by 1°C, moving the zone under which hydrates remain stable from a depth of around 360 metres to 396 metres. 'If this process becomes widespread along Arctic continental margins, tens of megatonnes of methane per year - equivalent to 5% to 10% of the total amount released globally by natural sources - could be released into the ocean,' said Graham Westbrook of the University of Birmingham in the UK. The researchers are now carrying out further investigations of the newly discovered plumes. 'Further exploration of hydrate and monitoring of methane release are needed to quantify the likely magnitude of future emissions,' the scientists conclude. The study is a contribution to the International Polar Year (IPY), which drew to a close earlier this year.

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