Hydrate Ridge is an accretionary thrust

clathrate hydrate Clathrate hydrates, or gas hydrates, clathrates, or hydrates, are crystalline water-based solids physically resembling ice, in which small non-polar molecules (typically gases) or polar molecules with large hydrophobic moieties are trapped ins ...

formation, meaning it has been made of sediment scraped off of

subducting Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second pla ...

oceanic plate. It is approx. 200 m (700 ft) high, and located 100 km (62 mi) offshore of

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

. At hydrate formations,

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

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 The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

community.

Significance

Hydrate Ridge and other hydrate formations store methane for extended periods of time. This methane can be released back into the ocean as a result of underwater

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

or other sudden movements. Methane is a potent

greenhouse gas Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...

, and the study of hydrate formations can lead to information about their influences on the

global carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...

and

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. It plays a crucial role in Climate change mitigation, limiting climate change by reducing the amount of Carbon dioxide in Earth's atmosphere, carbon dioxide in the atmosphe ...

. Because it is one of the most easily accessible hydrate formations in the ocean, and because the global effects of oceanic methane release are still poorly understood, Hydrate Ridge has received significant scientific attention since its discovery. The presence of venting sites and a benthic community there, along with the ridge's association with the

Cascadia Subduction Zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...

(as an accretionary formation), has made it a location at which gas hydrate and subduction zone characteristics are widely studied. Another motivation to study the ridge has been to uncover methane seeps as a potential source of

fossil fuels A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...

.Milkov, A.V.; and Sassen, R
"Economic geology of offshore gas hydrate accumulations and provinces."
''Marine and Petroleum Geology.'' 19.1 (2002): 1-11. Web. Research may reveal the economical value of these structures.

History of observations

The importance of Hydrate Ridge was recognized in 1986, with the discovery of low-temperature venting sites and a methane-driven biological community there.Kulm, L.D.; Suess, E.; Moore, J.C.; Carson, B.; Lewis, B.T.; Ritger, S.D.; Kadko, D.C.; Thornburg, T.M.; Embley, R.W.; Rugh, W.D.; Massoth, G.J.; Langseth, M.G.; Cochrane, G.R.; and Scamman, R.L
"Oregon subduction zone: venting, fauna, and carbonates."
''Science,'' 231 (1986): 561–566. Web. Since then, information has been collected on bubble emission frequencies, plume heights, etc. at the ridge, particularly via the use of ROVs, to further our scientific understanding of it.Denny, Alden R.; Solomon, Evan A.; Kelley, Deborah S.; and Philip, Brendan T
"Time-Series Measurements of Bubble Plume Variability and Water Column Methane Distribution above Southern Hydrate Ridge, Oregon."
''Geochemistry, Geophysics, Geosystems G³.'' 17.3 (2016): 1182-196. Web. A 2001 bubble plume study suggested that the free gas zone (see "Methane Venting") under surface sediments at Hydrate Ridge is thick. If this is the case, and if other active hydrate formations share this characteristic, more methane may be released (and influence

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

) than was anticipated prior to the study, according to researchers.Trehu, Anne M.; and Flueh, Ernst R
"Estimating the Thickness of the Free Gas Zone beneath Hydrate Ridge, Oregon Continental Margin, from Seismic Velocities and Attenuation."
''Journal of Geophysical Research: Solid Earth.'' 106.B2 (2001): 2035-045. Web. A 2016 study indicated that gas fluxes at Hydrate Ridge are affected more by diurnal patterns than by seasonal ones. The impacts of this require further study.

Subsurface structure

In 1996, the

Ocean Drilling Program The Ocean Drilling Program (ODP) was part of an international project to explore and study the composition and structure of Earth's oceanic basins. This collaborative effort spanned multiple decades and produced comprehensive data that improved un ...

deployed ocean bottom hydrophones and ocean bottom seismometers around Hydrate Ridge. The data from these tools was analyzed in a 2001 study, in which the velocities of refracted

seismic waves A seismic wave is a mechanical wave of acoustic wave, acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake (natural phenomenon), quake), types of volcanic eruptions ...

helped scientists estimate the subsurface contents of the site (e.g. the relative thickness of its free gas zone).

Methane venting

Methane is being released at Hydrate Ridge, particularly through

cold seeps A cold seep (sometimes called a cold vent) is an area of the ocean floor where seepage of fluids rich in hydrogen sulfide, methane, and other hydrocarbons occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature o ...

. The Southern Hydrate Ridge (SHR) is believed to be an especially active part of the formation. However, a 2016 study has asserted that the Summit of the SHR is not the sole structure involved in subseafloor gas and fluid transport. Smaller fluxes occur elsewhere. 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.

Biology

Hydrate Ridge houses several species of methane-utilizing benthic organisms, including '' Calyptogena'' clams and

microbial mats A microbial mat is a multi-layered sheet or biofilm of microbial colony (biology), colonies, composed of mainly bacteria and/or archaea. Microbial mats grow at interface (chemistry), interfaces between different types of material, mostly on submer ...

. A 2001 study proposed that the microbial mats at this site correlate to heavy outflow at cold seeps. It claimed, too, that ''Calyptogena'' function with the help of sulfide-oxidizing bacteria (sulfide is a product of methane oxidation).Tryon, Michael D.; and Brown, Kevin M
"Complex Flow Patterns through Hydrate Ridge and Their Impact on Seep Biota."
''Geophysical Research Letters.'' 28.14 (2001): 2863-866. Web. The aforesaid aligns with a 1986 study, which stated that several large organisms at Hydrate Ridge work

symbiotically Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term

microorganisms A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

to produce energy from methane.

Ocean Observatories Initiative Cabled Array

Part of the

Ocean Observatories Initiative The Ocean Observatories Initiative (OOI) is a National Science Foundation, National Science Foundation (NSF)]Major Research Facilitycomposed of a network of science-driven Ocean observations, ocean observing platforms and sensors (ocean observato ...

Cabled observatory, Cabled Array has been assembled on the Southern Hydrate Ridge. The cabled array collects and sends data on shore in real time. As a result, it enables scientists to make more, continuous observations of seasonal effects on vent activity, and of links between changes in methane flux and biochemical cycles at this specific location.

References

{{reflist Clathrate hydrates