In coastal ocean sediments, methane produced by decaying organic matter can collect in solid form. Known as a hydrate, this form of methane is stable at cold temperatures and high pressures. But when it’s brought to the surface, it converts from solid to gas, and the escaping methane can be ignited with a match.
More than one energy company is exploring ways to mine these methane deposits as a source of natural gas.
Of special concern is the fate of methane hydrate in the Arctic Ocean’s sediments. The increasing loss summer of sea ice is evidence that the Arctic Ocean is experiencing warming. Exposed seawater absorbs more solar energy than ice, reinforcing the warming trend. And the warming extends down to the ocean floor.
Over much of the continental shelf in the Arctic Ocean, sediments are trapped under a frozen layer that prevents methane from escaping. But, when water is deeper than about 60 feet, this permafrost is absent. As a result, methane in the sediment is free to turn to gas and bubble to the surface. Plumes of methane bubbles are widespread in deep waters.
If we were to experience a massive loss of methane from the Arctic, it would contribute significantly to the build-up of methane in the atmosphere, where it acts, like carbon dioxide, as a greenhouse gas. Essentially, a small amount of global warming could lead to a run-a-away greenhouse effect.
There is good evidence that massive releases of methane have occurred in the geologic past. We need to watch the Arctic closely.
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Photo, taken on September 15, 2011, courtesy of NASA Goddard Space Flight Center via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.