Methane Hydrate in Permafrost

The Arctic Circle is a vast region of frozen earth and sea. Concerns about global warming have opened the world’s eyes to the potential threat posed by Arctic thaw. The term Arctic thaw’ may bring to mind images of ice sheets calving into freezing, slushy waters or of polar bears driven to the brink of extinction. The true danger, however, lies with the methane present in Arctic sub-sea permafrost. There is such a large amount of methane gas present beneath the sea that it is referred to as the “Arctic Carbon Hyper Pool.”

Methane gas is a naturally occurring hydrocarbon (CH4) that is colorless and odorless. With a half-life of only twelve years, methane degrades to carbon dioxide (CO2), a greenhouse gas. Also a greenhouse gas, methane is twenty times more effective at holding solar radiation than carbon dioxide, making it potentially catastrophic.

Methane forms naturally in two ways: thermogenically and biogenically. Thermogenic methane is a product of time, high pressure and high temperature. Pockets of organic material deep within the earth’s crust are heated and crushed over long periods of time resulting in the formation of natural gas and oil. Biogenic methane is the metabolite of bacteria that feed on decayed organic matter. The greatest amount of methane in Arctic permafrost comes from biogenic production. Bacteria in the permafrost layer underneath the Arctic sea are so well adapted to their environment that they produce methane year-round.

To better understand the menace of Arctic thaw releasing methane, we should examine how methane exists there in such great quantities. The process by which methane becomes trapped in sub-sea permafrost is two-fold. Thermogenic methane is under great pressure and is less dense than water. When given the opportunity it will rise upward along fault lines or through porous material. At the permafrost layer, the bubbles stop, inhibited by the frozen mass above. Biogenic methane is produced in situ within the permafrost layer. Slight temperature increases cause the permafrost layer to become porous, allowing bubbles of gas to escape. Often the bubbles dissolve after traveling only a few hundred meters, so they do not reach the atmosphere. On the other hand, when enough methane is present under the permafrost and it encounters water, the subsequent reaction can form a crystalline solid, methane hydrate.

Specific conditions are necessary for the formation of methane hydrate, primarily low temperature and high pressure. These conditions are prevalent beneath the Arctic sub-sea permafrost. Methane hydrate, technically a clathrate (a substance in which a molecule of one chemical compound fills a cavity within the crystal lattice of another chemical compound, which in a hydrate is water) is a much more serious threat than bubbles of the gas. When methane hydrate has access to seawater it floats like ice. This convenient transport allows methane gas in the hydrate easy access to surface temperatures and pressures. Once out of their temperature and pressure zone, methane hydrates quickly dissociate (analogous to melting), releasing large amounts of methane gas into the atmosphere.

Global warming has been a hot topic for years. Whatever the root cause of recent warming trends, the consequences are undeniable. An increase in Arctic sub-sea permafrost temperatures of even a few degrees could set off a disastrous chain reaction. Termed methane burps,’ the sudden release of methane gas into the atmosphere would rapidly raise global temperatures. In turn, the higher temperatures would cause more methane release and spiral the planet into a potentially uninhabitable world. There is evidence in the geologic record of such events in the past, the worst of which nearly obliterated all life on earth.

Scientists continue to closely monitor the Arctic for signs of warming and thaw. There is little definitive evidence that points to global warming as the cause of current methane release in Arctic permafrost. Even so, the Arctic bears watching as a potential source of calamitous greenhouse warming.