Sewer Ice

Wednesday, May 28th, 2008

The ocean environment obviously plays a large role in any seasteading effort — but it’s not clear that “sewer ice” will play such a large role:

Methane hydrate is a crystalline solid that consists of methane surrounded by a cage of water molecules. It looks much like water ice. This strange substance, found in vast quantities in permafrost and on the ocean floor, has a fascinating history. Natural hydrates were first found in the 1930s when chlorine hydrate (a similar material with chlorine instead of methane) plugged natural gas pipelines. Most research focused on preventing their formation.

In the 1960s, scientists discovered naturally occuring methane hydrate in Siberian gas reservoirs. Before this period, methane hydrate was thought of as an unusual and unnatural substance that only occured in chem labs and gas pipelines. No one suspected that it was common in nature, let alone in the vast amounts which we currently estimate. Stable at depths greater than 300m, it melts quickly when removed from its natural environment. Because of this, it was not actually seen until 1974, when Soviet scientists successfully recovered nodules from the floor of the Black Sea.

Methane is the byproduct of bacterial breakdown of organic matter (ie “rotting”), which also creates hydrogen sulfide, which our noses recognize as sewer gas. Since organic material constantly falls to the ocean floor, in retrospect it makes sense that bacteria there digest it. On land, methane escapes into the atmosphere, but on the ocean floor, low temperatures and high pressures trap it into sewer ice.

The oceans have been around for quite awhile, and the earth’s reserves of this previously unknown substance are staggering. Methane hydrates are conservatively estimated to contain twice as much carbon as all other known fossil fuels, and this discovery means that scientists need to re-think the global carbon cycle. It has naturally been considered as a possible fuel, and a number of governments are digesting this possibility. Fantastic though it sounds, frozen flatulence may fuel the future!

More seriously, this discovery poses some serious worries on the global warming front. Methane is ten times more effective a greenhouse gas than carbon dioxide, and so much of it is trapped in hydrates that it could have a major effect on our climate. This might happen through a dangerous feedback loop. First, some other effect causes a slight warming of the earth, including its oceans. This melts some methane hydrate, releasing methane into the atmosphere. This adds to the greenhouse effect, making temperatures go up more, and the cycle repeats. In fact, Dr. Euan Nisbet of the University of Saskatchewan thinks this effect may have been behind the rapid climate change which followed the last glaciation.

The most recent twist in this strange tale comes from Monash University in Australia. Researchers there have theorized that some unexplained ship sinkings may have been caused by giant bubbles of methane. These bubbles are released occasionally when methane hydrate melts. If one of these bubbles comes up underneath a ship, the ship will briefly lose buoyancy (since its sitting on gas instead of water). Depending on the location of the bubble (experiments suggest that off to one side is the most dangerous), the ship may capsize. In fact, a sunken vessel has been found in the North Sea in the center of a large methane eruption site called the Witches Hole. As if drowning isn’t bad enough, imagine your last sensation being the overpowering smell of rotting eggs…

There is a lot of energy stored in the form of hydrates.

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