Methane ices: formation, distribution, and climate impact

¶ … Methane Ices

Methane ice is crystalline solids which look like ice, and which occur when water molecules form a cage-like structure around smaller methane molecules producing methane ices (Thomas).

Researchers have known for a long time that a mixture of water and a gas such as methane, in the right circumstances, form an ice-like substance called a clathrate, or gas hydrate, at temperatures above normal freezing point (The Economist). The term 'clathrate' more generally describes solids consisting of gases that are trapped within any kind of cage, while hydrate is the specific term for when the cage is made of water molecules (Robertson).

How Did They Form?

Ice has an open molecular structure. Add a bit of pressure and that openness structure will accommodate gas molecules. These, in turn, lend support to ice crystals that would otherwise melt. Pressure is one of the things that the bottom of the sea is famous for. So, if you add a source of methane, conditions there are often ideal for the formation of methane ice (The Economist).

Methane ice occurs naturally wherever the conditions within the sediments are in the methane-clathrate stability field, and where methane and water are available (Thomas).

This stability is limited by temperature and pressure: gas hydrates are stable at low temperatures and/or high pressures. Because of the requirements of pressure and temperature, and because of requirement of relatively large amounts of organic matter for bacterial methanogenesis, methane ice is mainly restricted to two regions: high latitudes and along the continental margins in the oceans (Thomas).

Where are they Located?

Most of these are in sediments of the ocean, but some are associated with permafrost soils. In polar regions the gas hydrates are commonly linked to permafrost occurrence onshore and on the continental shelves. In the oceans, gas hydrates are found on the outer continental margins, where the supply of organic material is high enough to generate enough methane, and water temperatures are close to freezing (Thomas).

Recent discoveries about the existence of a vast band of methane hydrate ice along the world's continental slopes, at approximately 500 meters deep, have revolutionized the theories of the Ice Age and global warming cycles (Methane Hydrate Ice).

What Impact may they have on Global Warming?

Key to understanding the gravity of climate destabilization is the wide array of catastrophic irreversible impacts that could amplify damage. One area of concern is methane hydrates ices (Robertson).