Deep sea communities currently remain largely unexplored, due the technological and logististical challenges and expense involved in visiting these remote biome

Biome

Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...

s. Because of the unique challenges (particularly the high barometric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

, extremes of temperature and absence of light

Aphotic zone

The aphotic zone is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates. Consequently, bioluminescence is essentially the only light found in this zone...

), it was long believed that little life existed in this hostile environment. Since the 19th century however, research has demonstrated that significant biodiversity

Biodiversity

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...

 exists in the deep sea.

The three main sources of energy and nutrients for deep sea communities are marine snow

Marine snow

In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...

, whale fall

Whale fall

Whale fall is the term used for a whale carcass that has fallen to the ocean floor. Whale falls were first observed in the 1980s, with the advent of deep-sea robotic exploration....

s, and chemosynthesis

Chemosynthesis

In biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...

 at hydrothermal vent

Hydrothermal vent

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

s and cold seep

Cold seep

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...

s.

History

Prior to the 19th century scientists assumed life was sparse in the deep ocean. In the 1870s Sir Charles Thompson

Sir Charles Thompson, 1st Baronet

Sir Charles Thompson, 1st baronet Thompson was a British naval officer. After long service in the Seven Years' War, American War of Independence and War of the First Coalition, he was Admiral John Jervis's second in command at the battle of Cape St Vincent...

 and colleagues aboard the Challenger expedition

Challenger expedition

The Challenger expedition of 1872–76 was a scientific exercise that made many discoveries to lay the foundation of oceanography. The expedition was named after the mother vessel, HMS Challenger....

 discovered many deep-sea creatures of widely varying types.

The first discovery of any deep-sea chemosynthetic community including higher animals was unexpectedly made at hydrothermal vents in the eastern Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 during geological explorations (Corliss et al., 1979). Two scientists, J. Corliss and J. van Andel, first witnessed dense chemosynthetic clam beds from the submersible DSV Alvin

DSV Alvin

Alvin is a manned deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in the same factory used to manufacture breakfast cereal-producing...

on February 17, 1977, after their unanticipated discovery using a remote camera sled two days before.

The Challenger Deep

Challenger Deep

The Challenger Deep is the deepest known point in the oceans, with a depth of to by direct measurement from submersibles, and slightly more by sonar bathymetry . It is located at the southern end of the Mariana Trench near the Mariana Islands group...

 is the deepest surveyed point of all of Earth's oceans; it is located at the southern end of the Mariana Trench

Mariana Trench

The Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about long but has a mean width of only...

 near the Mariana Islands

Mariana Islands

The Mariana Islands are an arc-shaped archipelago made up by the summits of 15 volcanic mountains in the north-western Pacific Ocean between the 12th and 21st parallels north and along the 145th meridian east...

 group. The depression is named after HMS Challenger, whose researchers made the first recordings of its depth on 23 March 1875 at station 225. The reported depth was 4,475 fathom

Fathom

A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom...

s (8184 meters) based on two separate soundings. In 1960, Don Walsh

Don Walsh

Don Walsh is an American oceanographer, explorer and marine policy specialist. He and Jacques Piccard were aboard the bathyscaphe Trieste when it made a record maximum descent into the Mariana Trench on 23 January 1960, the deepest point of the world's ocean...

 and Jacques Piccard

Jacques Piccard

Jacques Piccard was a Swiss oceanographer and engineer, known for having developed underwater vehicles for studying ocean currents. He was one of only two people, along with Lt...

 descended to the bottom of the Challenger Deep in the Trieste bathyscaphe

Bathyscaphe

A bathyscaphe is a free-diving self-propelled deep-sea submersible, consisting of a crew cabin similar to a bathysphere, but suspended below a float rather than from a surface cable, as in the classic bathysphere design....

. At this great depth a small flounder-like fish was seen moving away from the spotlight of the bathyscaphe. Since then, no manned craft has ever returned to the Challenger Deep.

The Japanese remote operated vehicle (ROV) Kaiko

Kaiko

was a remotely operated underwater vehicle built by the Japan Agency for Marine-Earth Science and Technology for exploration of the deep sea. Kaikō was the second of only three vessels ever to reach the bottom of the Challenger Deep, as of 2010...

became the second vessel to reach the bottom of the Challenger Deep in March 1995. Nereus

Nereus (underwater vehicle)

Nereus is a hybrid autonomous underwater vehicle built by the Woods Hole Oceanographic Institution . Constructed as a research vehicle to operate at depths of up to , it was designed to explore Challenger Deep, the deepest surveyed point in the global ocean...

, a hybrid remotely operated vehicle (HROV) of the Woods Hole Oceanographic Institution

Woods Hole Oceanographic Institution

The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...

, is currently the only vehicle capable of exploring ocean depths beyond 7000 meters. Nereus reached a depth of 10,902 meters at the Challenger Deep on May 31, 2009. On 1 June 2009, sonar mapping of the Challenger Deep by the Simrad

Simrad Optronics

, is the holding company of Simrad Optronics Group located at Nøtterøy, Norway. Simrad Optronics Group is a global niche supplier to the defence industry, with production facilities in Norway and Maine, USA. Daughter companies include Vinghøg AS at Nøtterøy, Norway and Vingtech Corporation in...

 EM120 multibeam sonar bathymetry system aboard the R/V Kilo Moana

RV Kilo Moana (T-AGOR-26)

R/V Kilo Moana is a small waterplane area twin hull oceanographic research ship owned by the US Navy and operated by the University of Hawaii as a part of the University-National Oceanographic Laboratory System fleet. She was designed to operate in coastal and blue water areas...

 indicated a maximum depth of 10971 meters (6.82 miles). The sonar system uses phase

Phase (waves)

Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

 and amplitude

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

 bottom detection, with an accuracy of better than 0.2% of water depth (this is an error of about 22 meters at this depth).

The first discovery of any deep-sea chemosynthetic community including higher animals was unexpectedly made at hydrothermal vents in the eastern Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 during geological explorations (Corliss et al., 1979). Two scientists, J. Corliss and J. van Andel, first witnessed dense chemosynthetic clam beds from the submersible DSV Alvin

DSV Alvin

Alvin is a manned deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in the same factory used to manufacture breakfast cereal-producing...

on February 17, 1977, after their unanticipated discovery using a remote camera sled two days before.

Lack of light

The ocean can be conceptualized as being divided into various zones

Oceanic zone

The oceanic zone begins in the area off shore where the water measures 200 meters deep or deeper.It is the region of open sea beyond the edge of the continental shelf and includes 65% of the ocean’s completely open water...

, depending on depth, and presence or absence of sunlight

Sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

. Nearly all life forms

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 in the ocean depend on the photosynthetic

Photosynthesis

Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 activities of phytoplankton

Phytoplankton

Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 and other marine plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s to convert carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 into organic carbon

Total organic carbon

Total organic carbon is the amount of carbon bound in an organic compound and is often used as a non-specific indicator of water quality or cleanliness of pharmaceutical manufacturing equipment....

, which is the basic building block of organic matter

Organic matter

Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...

. Photosynthesis in turn requires energy from sunlight to drive the chemical reactions that produce organic carbon.

The stratum of the water column nearest the surface of the ocean (sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

) is referred to as the photic zone

Photic zone

The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...

. The photic zone can be subdivided into two different vertical regions. The uppermost portion of the photic zone, where there is adequate light to support photosynthesis by phytoplankton and plants, is referred to as the euphotic zone (also referred to as the epipelagic zone, or surface zone). The lower portion of the photic zone, where the light intensity is insufficient for photosynthesis, is called the disphotic zone (disphotic means "poorly lit" in Greek). The disphotic zone is also referred to as the mesopelagic zone, or the twilight zone. Its lowermost boundary is at a thermocline

Thermocline

A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...

 of 12 °C (53.6 °F), which, in the tropics

Tropics

The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 generally lies between 200 and 1000 meters.

The euphotic zone is somewhat arbitrarily defined as extending from the surface to the depth where the light intensity is approximately 0.1–1% of surface sunlight irradiance

Insolation

Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

, depending on season

Season

A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...

, latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 and degree of water turbidity

Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....

. In the clearest ocean water, the euphotic zone may extend to a depth of about 150 meters, or rarely, up to 200 meters. Dissolved substances

Solution

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

 and solid particles

Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...

 absorb and scatter light, and in coastal regions the high concentration of these substances causes light to be attenuated rapidly with depth. In such areas the euphotic zone may be only a few tens of meters deep or less. The disphotic zone, where light intensity is considerably less than 1% of surface irradiance, extends from the base of the euphotic zone to about 1000 meters. Extending from the bottom of the photic zone down to the seabed

Seabed

The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

 is the aphotic zone

Aphotic zone

The aphotic zone is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1% of sunlight penetrates. Consequently, bioluminescence is essentially the only light found in this zone...

, a region of perpetual darkness.

Since the average depth of the ocean is about 4300 meters, the photic zone represents only a tiny fraction of the ocean’s total volume. However, due to its capacity for photosynthesis, the photic zone has the greatest biodiversity and biomass

Biomass (ecology)

Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...

 of all oceanic zones. Nearly all primary production

Primary production

400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...

 in the ocean occurs here. Any life forms present in the aphotic zone must either be capable of movement upwards through the water column

Diel vertical migration

Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...

 into the photic zone for feeding, or must rely on material sinking from above

Marine snow

In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...

, or must find another source of energy and nutrition, such as occurs in chemosynthetic

Chemosynthesis

In biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...

 archaea

Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

 found near hydrothermal vent

Hydrothermal vent

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

s and cold seep

Cold seep

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...

s.

Hyperbaricity

These animals have evolved

Natural selection

Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

 to survive the extreme pressure of the sub-photic zone

Photic zone

The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...

s. The pressure increases by about one atmosphere every ten meters. To cope with the pressure, many fish are rather small, usually not exceeding 25 cm in length. Also, scientists have discovered that the deeper these creatures live, the more gelatinous their flesh and more minimal their skeletal structure. These creatures have also eliminated all excess cavities that would collapse under the pressure, such as swim bladders.

Pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 is the greatest environmental factor acting on deep-sea organisms. In the deep sea, although most of the deep sea is under pressures between 200 and 600 atm, the range of pressure is from 20 to 1,000 atm. Pressure exhibits a great role in the distribution of deep sea organisms. Until recently, people lacked detailed information on the direct effects of pressure on most deep-sea organisms, because virtually all organisms trawled from the deep sea arrived at the surface dead or dying. With the advent of traps that incorporate a special pressure-maintaining chamber, undamaged larger metazoan animals have been retrieved from the deep sea in good condition. Some of these have been maintained for experimental purposes, and we are obtaining more knowledge of the biological effects of pressure.

Temperature

The two areas of greatest and most rapid temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 change in the oceans are the transition zone between the surface waters and the deep waters, the thermocline, and the transition between the deep-sea floor and the hot water flows at the hydrothermal vents. Thermoclines vary in thickness from a few hundred meters to nearly a thousand meters. Below the thermocline, the water mass of the deep ocean is cold and far more homogeneous. Thermoclines are strongest in the tropics, where the temperature of the epipelagic zone is usually above 20°C. From the base of the epipelagic, the temperature drops over several hundred meters to 5 or 6°C at 1,000 meters. It continues to decrease to the bottom, but the rate is much slower. Below 3,000 to 4,000 m, the water is isothermal. At any given depth, the temperature is practically unvarying over long periods of time. There are no seasonal temperature changes, nor are there any annual changes. No other habitat on earth has such a constant temperature.

Hydrothermal vents are the direct contrast with constant temperature. In these systems, the temperature of the water as it emerges from the "black smoker" chimneys may be as high as 400°C (it is kept from boiling by the high hydrostatic pressure) while within a few meters it may be back down to 2 - 4°C.

Salinity

Salinity

Salinity

Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 is remarkably constant throughout the depths of the deep sea. There are two notable exceptions to this rule:

1. In the Mediterranean Sea

Mediterranean Sea

The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

, water loss through evaporation

Evaporation

Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

 greatly exceeds input from precipitation

Precipitation (meteorology)

In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

 and river runoff. Because of this, salinity in the Mediterranean is higher than in the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

. Evaporation is especially high in its eastern half, causing the water level to decrease and salinity to increase in this area. The resulting pressure gradient pushes relatively cool, low-salinity water from the Atlantic Ocean across the basin. This water warms and becomes saltier as it travels eastward, then sinks in the region of the Levant

Levant

The Levant or ) is the geographic region and culture zone of the "eastern Mediterranean littoral between Anatolia and Egypt" . The Levant includes most of modern Lebanon, Syria, Jordan, Israel, the Palestinian territories, and sometimes parts of Turkey and Iraq, and corresponds roughly to the...

 and circulates westward, to spill back into the Atlantic over the Strait of Gibraltar

Strait of Gibraltar

The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

. The net effect of this is that at the Strait of Gibraltar, there is an eastward surface current of cold water of lower salinity from the Atlantic, and a simultaneous westward current of warm saline water from the Mediterranean in the deeper zones. Once back in the Atlantic, this chemically distinct Mediterranean Intermediate Water can persist for thousands of kilometers away from its source.

2. Brine pool

Brine pool

Brine pools are large areas of brine on the ocean basin. These pools are bodies of water that have a salinity three to five times greater than the surrounding ocean. For deep-sea brine pools, the source of the salt is the dissolution of large salt deposits through salt tectonics...

s are large areas of brine

Brine

Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

 on the seabed

Seabed

The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

. These pools are bodies of water that have a salinity that is three to five times greater than that of the surrounding ocean. For deep sea brine pools the source of the salt is the dissolution of large salt

Sodium chloride

Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

 deposits through salt tectonics

Salt tectonics

500px|thumb|rightSalt tectonics is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks...

. The brine often contains high concentrations of methane, providing energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 to chemosynthetic

Chemosynthesis

In biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...

 extremophile

Extremophile

An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...

s that live in this specialized biome

Biome

Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...

. Brine pools are also known to exist on the Antarctic continental shelf

Antarctic continental shelf

The Antarctic continental shelf is a geological feature that underlies the Southern Ocean, surrounding the continent of Antarctica. The shelf is generally narrow and unusually deep, its edge lying at depths of 400 to 800 meters . It is home to a thriving ecosystem of penguins and cold-water fish....

 where the source of brine is salt excluded during formation of sea ice

Sea ice

Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....

. Deep sea and Antarctic brine pools can be toxic to marine animals. Brine pools are sometimes called seafloor lakes because the dense brine creates a halocline

Halocline

In oceanography, a halocline is a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity affects the density of seawater, it can play a role in its vertical stratification...

 which does not easily mix with overlying seawater. The high salinity raises the density of the brine, which creates a distinct surface and shoreline for the pool.

The deep sea

Deep sea

The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...

, or deep layer, is the lowest layer in the ocean, existing below the thermocline, at a depth of 1000 fathoms (1800 m) or more. The deepest part of the deep sea is Mariana Trench

Mariana Trench

The Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about long but has a mean width of only...

 located in the western North Pacific. It is also the deepest point of the earth's crust. It has a maximum depth of about 10.9 km which is deeper than the height of Mount Everest

Mount Everest

Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...

. In 1960, Don Walsh

Don Walsh

Don Walsh is an American oceanographer, explorer and marine policy specialist. He and Jacques Piccard were aboard the bathyscaphe Trieste when it made a record maximum descent into the Mariana Trench on 23 January 1960, the deepest point of the world's ocean...

 and Jacques Piccard

Jacques Piccard

Jacques Piccard was a Swiss oceanographer and engineer, known for having developed underwater vehicles for studying ocean currents. He was one of only two people, along with Lt...

 reached the bottom of Mariana Trench in the Trieste bathyscaphe. The pressure is about 11,318 metric tons-force

Kilogram-force

A kilogram-force , or kilopond , is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a gravitational field...

 per square meter (110.99 MPa or 16100 psi

Pounds per square inch

The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...

).

Marine snow

The upper photic zone of the ocean is filled with particle organic matter (POM) and is quite productive, especially in the coastal areas and the upwelling areas. However, most POM is small and light. It may take hundreds, or even thousands of years for these particles to settle through the water column into the deep ocean. This time delay is long enough for the particles to be remineralized and taken up by organisms in the food webs.

Scientists at Woods Hole Oceanographic Institution conducted an experiment three decades ago in deep Sargasso Sea looking at the rate of sinking. They found what became known as marine snow

Marine snow

In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...

 in which the POM are repackaged into much larger particles which sink at much greater speed, 'falling like snow'.

Because of the sparsity of food, the organisms living on and in the bottom are generally opportunistic. They have special adaptations for this extreme environment: rapid growth, effect larval dispersal mechanism and the ability to use a ‘transient’ food resource. One typical example is wood-boring bivalves, which bore into wood and other plant remains and are fed on the organic matter from the remains.

Whale falls

For the deep-sea creature, a dead whale is the most exciting event. A dead whale can bring hundreds of tons of organic matter to the bottom. Whale fall

Whale fall

Whale fall is the term used for a whale carcass that has fallen to the ocean floor. Whale falls were first observed in the 1980s, with the advent of deep-sea robotic exploration....

 community progresses through three stages:

1. Mobile scavenger stage: Big and mobile deep-sea animals arrive at the site almost immediately after whales fall on the bottom. Amphipods, crab
   Crab
   True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
   
   s, sleeper sharks and hagfish
   Hagfish
   Hagfish, the clade Myxini , are eel-shaped slime-producing marine animals . They are the only living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils whose next nearest relatives include all vertebrates...
   
    are all scavengers.
2. Opportunistic stage: One interesting genus is Osedax
   Osedax
   Osedax is a genus of deep-sea siboglinid polychaetes, commonly called boneworms, zombie worms, or bone-eating worms, or bone-eating snot flowers...
   
   . Osedax is an interesting tubeworm. The larva is born without sex. The surrounding environment determines the sex of the larva. When a larva settles on a whale bone, it turns into a female; when a larva settles on or in a female, it turns into a dwarf male. One female Osedax can carry more than 200 of these male individuals in its oviduct.
3. Sulfophilic stage: Further decomposition of bones and seawater sulfate reduction happen at this stage. Bacteria create a sulphide-rich environment analogous to hydrothermal vents. Polynoids, bivalves, gastropods and other sulphur-loving creatures move in.

Hydrothermal vents

Hydrothermal vents, also called black smokers, were discovered in 1977 by scientists from Scripps Institution of Oceanography. So far, the discovered hydrothermal vents are all located at the boundaries of plates: East Pacific, California, Mid-Atlantic ridge, China and Japan.

New ocean basin material is being made in regions such as the Mid-Atlantic ridge as tectonic plates pull away from each other. The rate of spreading of plates is 1–5 cm/yr. Cold sea water circulates down through cracks between two plates and heats up as it passes through hot rock. Minerals and sulfides are dissolved into the water during the interaction with rock. Eventually the hot solutions emanate from an active sub-seafloor rift creating a black smoker.

Chemosynthesis of bacteria provide the energy and organic matter for the whole food web in vent ecosystems. Giant tubeworms can grow to 2.4 metre
tall because of the richness of nutrients. By now, over 300 new species have been discovered at hydrothermal vents.

Hydrothermal vents are entire ecosystems totally separated from the world of light. And they may be the first evidence that the earth can support life without the sun.

Cold seeps

A cold seep

Cold seep

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...

 (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

, methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and other hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

-rich fluid seepage occurs, often in the form of a brine pool

Brine pool

Brine pools are large areas of brine on the ocean basin. These pools are bodies of water that have a salinity three to five times greater than the surrounding ocean. For deep-sea brine pools, the source of the salt is the dissolution of large salt deposits through salt tectonics...

.