Methane clathrate is a form of water ice that contains a large amount of methane within its crystal structure (a clathrate hydrate) and recently extremely large deposits of methane clathrates have been found under sediments on the ocean floors of Earth. Methane clathrates are common constituents of the shallow marine geosphere, and they occur both in deep sedimentary structures, and as outcrops on the ocean floor. Methane hydrates are believed to form by migration of gas from depth along geological faults, followed by precipitation, or crystallization, on contact of the rising gas stream with cold sea water.
Methane ice may be involved in the fluctuations of atmospheric methane seen in polar ice cores. From this record, it is known that methane rose rapidly whenever climate changed from glacial to interglacial conditions (during "deglaciation"). Warming of water bathing the seafloor could have led to large-scale release of methane from the melting of methane ice. Evidence for such a process is seen on the floor of the Barents Sea, which is the shelf sea north of Norway and forms part of the Arctic. Fields of giant craters have been detected within that sea off the coast of Norway, in a region rich in methane clathrate deposits. The biggest of the craters was measured as 700 m wide and 30 m deep, indicating catastrophic explosions of methane. It is thought that these craters were formed during deglaciation.
Direct measurements show that large amounts of methane can escape from the Sea of Okhotsk on occasion, where the seafloor is rich in organic matter and harbors methane ice. Pressure is increased on the seafloor during deglaciation (from the rise in sea level). Thus, if the seafloor is the source of the methane increase seen in ice cores, a marked rise in temperature must be responsible for release of methane. This would imply that intermediate waters must have been considerably colder than now, during glacial time. Also, the contribution of large amounts of methane would provide an additional source for the increase of carbon dioxide observed during deglaciation. Evidence for catastrophic release of methane has been found in the more distant geologic record as well, within deep-sea sediments, for a period at the end of the Paleocene about 55 million years ago. The event led to widespread extinctions in the fauna living on the deep-sea floor.
What is now worrying scientists is that global warming caused by the Greenhouse Effect, may raise sea temperatures, melting polar ice and releasing large amounts of methane trapped in the methane clathrate resevoirs. Methane is a far more potent greenhouse gas than Carbon dioxide and the release of large volumes could cause a positive feedback reaction - raising the rate of climate warming. Another strange side affect could be a drop in sea levels due to the gap left behind from the methane clathrate melt.
In the worst circumstances, the "hole" left behind could result in a sea level drop of 25 metres but Dr Bratton of the US Geological Survey has stated that his conservative estimates suggest a drop of up to 1.5m. He also believes that a 1-2 degree rise in temperature in polar regions could be enough to start the melting of the clathrates - more worryingly arctic temperatures are modelled to rise more quickly than other regions around the globe so we may well be reaching a point at which climate change could accelerate to catastrophic levels.
Furthermore it is believe that methane is already being released by the melt of the siberian tundra -
Siberia's rapid thaw causes alarm
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