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Methane clathrate (CH4·5.75H2O) or (8CH4·46H2O), 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. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth. Methane hydrate is formed when hydrogen-bonded water and methane gas come into contact at high pressures and low temperatures in oceans.
Clathrate hydrates, or gas hydrates, clathrates, hydrates, etc., are crystalline water-based solids physically resembling ice, in which small non-polar molecules or polar molecules with large hydrophobic moieties are trapped inside "cages" of hydrogen bonded, frozen water molecules. In other words, clathrate hydrates are clathrate compounds in which the host molecule is water and the guest molecule is typically a gas or liquid. Without the support of the trapped molecules, the lattice structure of hydrate clathrates would collapse into conventional ice crystal structure or liquid water. Most low molecular weight gases, including O2, H2, N2, CO2, CH4, H2S, Ar, Kr, and Xe, as well as some higher hydrocarbons and freons, will form hydrates at suitable temperatures and pressures. Clathrate hydrates are not officially chemical compounds, as the enclathrated guest molecules are never bonded to the lattice. The formation and decomposition of clathrate hydrates are first order phase transitions, not chemical reactions. Their detailed formation and decomposition mechanisms on a molecular level are still not well understood. Clathrate hydrates were first documented in 1810 by Sir Humphry Davy who found that water was a primary component of what was earlier thought to be solidified chlorine.
Coalbed methane extraction is a method for extracting methane from a coal deposit. Coal bed methane (CBM) is one of the factors restricting safe production of coal in underground coal mines. It is also a form of high-quality energy that can be used in many fields such as power generation, heating, and chemical industries. CBM extraction is therefore carried out prior to extraction with a view of increasing the safety of mining coal beds, and as a useful energy resource to be exploited.
Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface is underlain by permafrost, including substantial areas of Alaska, Greenland, Canada and Siberia. It can also be located on mountaintops in the Southern Hemisphere and beneath ice-free areas in the Antarctic.
The Paleocene–Eocene thermal maximum (PETM), alternatively "Eocene thermal maximum 1" (ETM1), and formerly known as the "Initial Eocene" or "Late Paleocene thermal maximum", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event occurred at the time boundary of the Paleocene and Eocene geological epochs. The exact age and duration of the event is uncertain but it is estimated to have occurred around 55.5 million years ago.
A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.
The clathrate gun hypothesis is a proposed explanation for the periods of rapid warming during the Quaternary. The idea is that changes in fluxes in upper intermediate waters in the ocean caused temperature fluctuations that alternately accumulated and occasionally released methane clathrate on upper continental slopes. These events would have caused the Bond Cycles and individual interstadial events, such as the Dansgaard–Oeschger interstadials.
Carbon dioxide hydrate or carbon dioxide clathrate is a snow-like crystalline substance composed of water ice and carbon dioxide. It normally is a Type I gas clathrate. There has also been some experimental evidence for the development of a metastable Type II phase at a temperature near the ice melting point. The clathrate can exist below 283K (10 °C) at a range of pressures of carbon dioxide. CO2 hydrates are widely studied around the world due to their promising prospects of carbon dioxide capture from flue gas and fuel gas streams relevant to post-combustion and pre-combustion capture. It is also quite likely to be important on Mars due to the presence of carbon dioxide and ice at low temperatures.
The Nankai Trough is a submarine trough located south of the Nankaidō region of Japan's island of Honshu, extending approximately 900 km (559 mi) offshore. The underlying fault, the Nankai megathrust, is the source of the devastating Nankai megathrust earthquakes, while the trough itself is potentially a major source of hydrocarbon fuel, in the form of methane clathrate.
Arctic methane release is the release of methane from seas and soils in permafrost regions of the Arctic. While it is a long-term natural process, methane release is exacerbated by global warming. This results in a positive feedback cycle, as methane is itself a powerful greenhouse gas.
A methane chimney or gas chimney is a rising column of natural gas, mainly methane within a water or sediment column. The contrast in physical properties between the gas phase and the surrounding water makes such chimneys visible in oceanographic and geophysical data. In some cases, gas bubbles released at the seafloor may dissolve before they reach the ocean surface, but the increased hydrocarbon concentration may still be measured by chemical oceanographic techniques.
The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir that is seldom considered when determining global terrestrial carbon reservoirs. Recent and ongoing scientific research however, is changing this view.
Mount Elbert Methane Hydrate Site
The Mallik Methane Hydrate Site is located in the Beaufort Sea, Canada.
Nankai Methane Hydrate Site is located in the Nankai Trough, Japan.
Hydrate Ridge is an accretionary thrust clathrate hydrate formation, meaning it has been made of sediment scraped off of subducting oceanic plate. It is approx. 200 m high, and located 100 km offshore of Oregon. At hydrate formations, methane is trapped in crystallized water structures. Such methane transforms into the gaseous phase and seeps into the ocean at this site, which has been a popular location of study since its discovery in 1986. Hydrate Ridge also supports a methane-driven benthic community.
Nitrogen clathrate or nitrogen hydrate is a clathrate consisting of ice with regular crystalline cavities that contain nitrogen molecules. Nitrogen clathrate is a variety of air hydrates. It occurs naturally in ice caps on Earth, and is believed to be important in the outer Solar System on moons such as Titan and Triton which have a cold nitrogen atmosphere.
Southern Hydrate Ridge, located about 90 km offshore Oregon Coast, is an active methane seeps site located on the southern portion of Hydrate Ridge. It extends 25 km in length and 15 km across, trending north-northeast-south-southwest at the depth of approximately 800 m. Southern Hydrate Ridge has been the site of numerous submersible dives with the human occupied Alvin submarine, extensive visits by numerous robotic vehicles including the Canadian ROV ROPOS, Jason , and Tiburon (MBARI), and time-series geophysical studies that document changes in the subsurface distribution of methane. It is also a key site of the National Science Foundations Regional Cabled Array that is part of the Ocean Observatories Initiative (OOI), which includes eight types of cabled instruments streaming live data back to shore 24/7/365 at the speed of light, as well as uncabled instruments.
NOASS Okeanos Explorer Gulf of Mexico 2017 Expedition was the first of three expeditions on the NOAAS Okeanos Explorer intended to increase the understanding of the deep-sea environment in the Gulf of Mexico. Gulf of Mexico 2017 was a 23-day telepresence-enabled expedition focused on acquiring data on priority exploration areas identified by ocean management and scientific communities. The goal of the expedition was to use remotely operated vehicle (ROV) dives and seafloor mapping operations to increase the understanding of the deep-sea ecosystems in these areas to support management decisions. Many of the areas had no sonar data, these areas were top priority for high-resolution bathymetry collection. The expedition established a baseline of information in the region to catalyze further exploration, research, and management activities. The expedition lasted from 29 November 2017 to 21 December 2017.
Bottom simulating reflectors (BSRs) are, on seismic reflection profiles, shallow seismic reflection events, characterized by their reflection geometry similar to seafloor bathymetry. . They have, however, the opposite reflection polarity to the seabed reflection, and frequently intersect the primary reflections.
References
- ↑ Kvenvolden, Keith (1993). "Gas Hydrates: Geological Perspective and Global Change" (PDF). Reviews of Geophysics. 31 (2): 173. Bibcode:1993RvGeo..31..173K. doi:10.1029/93rg00268.
- ↑ MacKay, Mary; Jarrard, Richard; Westbrook, Graham; Hyndman, Roy (May 1994). "Origin of bottom simulating reflectors: Geophysical evidence from the Cascadia accretionary prism" (PDF). Geology. 22 (5): 459–462. Bibcode:1994Geo....22..459M. doi:10.1130/0091-7613(1994)022<0459:oobsrg>2.3.co;2.
- ↑ Thomas, Ellen. "Clathrates: little know components of the global carbon cycle". wesleyan.edu.
- ↑ M. D., Max; A., Lowrie (1997). "Oceanic Methane Hydrate Development: Reservoir Character and Extraction". Offshore Technology Conference: 235.
- ↑ Grauls, Dominique (2001). "Gas hydrates: importance and applications in petroleum exploration". Marine and Petroleum Geology . 18 (4): 519–523. doi:10.1016/s0264-8172(00)00075-1.