gas hydrates

gas hydrates A hydrate, or clathrate, is a solid, ice-like substance composed of rigid cages of water molecules enclosing gas molecules. Low temperatures (4–6 °C), high pressures (above 50 atmospheres), and gas concentrations exceeding solubility are necessary for their formation. The two components are not chemically bonded, but are linked by van der Waals forces.

Naturally occurring gas hydrates are present in polar continental regions and continental margin marine sediments. In marine sediments hydrate layers usually occur below the sea floor, where their presence can be detected by seismic reflections parallel to the topography of the sea bed. The gas component may be ethane, propane, butane, carbon dioxide, or hydrogen sulphide, but is most commonly methane. One volume of methane hydrate may contain 164 volumes of methane gas. Hydrate deposits generally contain biogenic methane, generated from bacterial anaerobic degradation of organic matter, rather than thermogenic methane derived from the breakdown of organic matter at high temperatures.

Gas hydrates have global significance as a potential energy resource. Most natural gas on Earth is in the form of hydrates, and estimates indicate that methane hydrates contain twice the carbon contained in all known fossil-fuel deposits. Hydrate breakdown contributes to global warming, since methane is a ‘greenhouse gas’. Geological evidence indicates that rapid falls in sea level and warming of the deep ocean have occurred in the past, destabilizing the gas hydrate and releasing methane, which can cause global warming. Gas hydrate dissociation is also linked to submarine landslides, which can generate tsunamis.

R. John Parkes