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Methane clathrate (CH 4 ·5.75H 2 O) or (4CH 4 ·23H 2 O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice.
Naturally on Earth gas hydrates can be found on the seabed, in ocean sediments, [22] in deep lake sediments (e.g. Lake Baikal), as well as in the permafrost regions. The amount of methane potentially trapped in natural methane hydrate deposits may be significant (10 15 to 10 17 cubic metres), [ 23 ] which makes them of major interest as a ...
The present-day global methane hydrate reserve was once considered to be between 2,000 and 10,000 Gt C (billions of tons of carbon), but is now estimated between 1500 and 2000 Gt C. [37] However, because the global ocean bottom temperatures were ~6 °C higher than today, which implies a much smaller volume of sediment hosting gas hydrate than ...
The free gas zone is a zone of freed methane in a hydrate formation, beneath the hydrate stability zone. It can influence the rate of methane output at a ridge or ridge region. A large free gas zone makes more methane available to be released into the open ocean, and, thus, can likely be more influential on climate change than a smaller one. [11]
The Nankai Trough is located beneath the Pacific Ocean off the southeast coast of Japan, and extends more than 700 km in a southwest-northward trending direction. The Nankai Trough is not only known as an active subduction and earthquake zone, but also for its large clathrate hydrate deposits occurring on the shelf and continental slope.
Methane ice at Southern Hydrate Ridge has been found within the shallow sediments, and more rarely exposed on the seafloor. Because Southern Hydrate Ridge is located on the upper continental slope , the regional hydrate stability zone (RHSZ) , which is controlled by the sediment pore pressure and temperature, [ 6 ] is very shallow. [ 7 ]
Methane clathrates feature the hydrogen-bonded framework contributed by water and the guest molecules of methane. Large amounts of methane naturally frozen in this form exist both in permafrost formations and under the ocean sea-bed. [8] Other hydrogen-bonded networks are derived from hydroquinone, urea, and thiourea.
The existence and depth of a hydrate deposit is often indicated by the presence of a bottom-simulating reflector (BSR). A BSR is a seismic reflection indicating the lower limit of hydrate stability in sediments due to the different densities of hydrate saturated sediments, normal sediments and those containing free gas. [2]