See Also

Underwater

Underwater, sometimes shortened as U/W, is a term describing the realm below the surface of water Water

Water is a taste [i]less, odor [i]less substance that is essential to all known forms of life [i] and i ... 

 where the water exists in a natural feature such as an ocean Ocean

Oceans cover almost three quarters of the surface of the Earth [i], and nearly half of the world's mar ... 

, sea Sea

A sea is a large expanse of saline water [i] connected with an ocean [i], or a large, usually s ... 

, lake Lake

A lake is a body of water or other liquid of considerable size surrounded by land.... 

, pond Pond

A pond is a body of water smaller than a lake [i]. However the difference between a pond and a lake is ... 

, or river River

A river is a large natural waterway [i]. ... 

. Three quarters of the planet earth is covered by water. A majority of the planet's solid surface is abyssal plain, at depths between 4000 and 5500 m below the surface of the oceans. The solid surface location on the planet closest to the center of the orb is the Challenger Deep Challenger Deep

The Challenger Deep is the deepest known point in the oceans.... 

, located in the Mariana Trench Mariana Trench

The Mariana Trench is the deepest known submarine trench [i], and the deepest location in the Earth [i]... 

 at a depth of 10,924 m  under the sea. Although a number of human Human

Humans, or human beings, are biped [i]al primate [i]s belonging to the mammal [i]ian species ... 

 activities are conducted underwater—such as scuba diving Scuba diving

Scuba diving is the term used to describe the use of a self-contained breathing set [i] to stay underwater [i] ... 

 for work Commercial Diving

Commercial Diving is a branch of professional diving [i] where the divers are paid and ... 

 or recreation Recreational diving

Recreational diving is a type of diving [i] that uses SCUBA equipment [i] fo ... 

, or even underwater warfare with submarines Submarine

A submarine is a specialized watercraft [i] that can operate underwater [i]. ... 

—this very extensive environment

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Underwater, sometimes shortened as U/W, is a term describing the realm below the surface of water Water

Water is a taste [i]less, odor [i]less substance that is essential to all known forms of life [i] and i ... 

 where the water exists in a natural feature such as an ocean Ocean

Oceans cover almost three quarters of the surface of the Earth [i], and nearly half of the world's mar ... 

, sea Sea

A sea is a large expanse of saline water [i] connected with an ocean [i], or a large, usually s... 

, lake Lake

A lake is a body of water or other liquid of considerable size surrounded by land.... 

, pond Pond

A pond is a body of water smaller than a lake [i]. However the difference between a pond and a lake is ... 

, or river River

A river is a large natural waterway [i]. ... 

. Three quarters of the planet earth is covered by water. A majority of the planet's solid surface is abyssal plain, at depths between 4000 and 5500 m below the surface of the oceans. The solid surface location on the planet closest to the center of the orb is the Challenger Deep Challenger Deep

The Challenger Deep is the deepest known point in the oceans.... 

, located in the Mariana Trench Mariana Trench

The Mariana Trench is the deepest known submarine trench [i], and the deepest location in the Earth [i]... 

 at a depth of 10,924 m  under the sea.

Although a number of human Human

Humans, or human beings, are biped [i]al primate [i]s belonging to the mammal [i]ian species ... 

 activities are conducted underwater—such as scuba diving Scuba diving

Scuba diving is the term used to describe the use of a self-contained breathing set [i] to stay underwater [i] ... 

 for work Commercial Diving

Commercial Diving is a branch of professional diving [i] where the divers are paid and ... 

 or recreation Recreational diving

Recreational diving is a type of diving [i] that uses SCUBA equipment [i] fo ... 

, or even underwater warfare with submarines Submarine

A submarine is a specialized watercraft [i] that can operate underwater [i].... 

—this very extensive environment on planet earth Earth

Earth is the third planet [i] in the solar system [i] in terms of distance from the Sun [i], and the fi ... 

 is hostile to humans in many ways and therefore little explored.

An immediate obstacle to human activity under water is the fact that human lung Lung

The lung is the essential respiration organ [i] in air-breathing vertebrate [i]s. ... 

s cannot naturally function in this environment. Unlike the gill Gill

In aquatic organisms, gills are respiration organ [i]s for the extraction of oxygen [i] from water [i] a ... 

s of fish Fish

A fish is a water [i]-dwelling vertebrate [i] with gills [i], that remains so throughout its life.... 

, human lung Lung

The lung is the essential respiration organ [i] in air-breathing vertebrate [i]s. ... 

s are adapted to the exchange of gases at atmospheric pressure Pressure

Pressure is the force [i] per unit area [i] applied on a surface in a direction perpendicular [i] ... 

, not liquid Liquid

A liquid is one of the main phases of matter [i]. ... 

s. Aside from simply having insufficient musculature to rapidly move water in and out of the lungs, a more significant problem for all air breathing animals, such as mammals and bird Bird

Birds are biped [i]al, warm-blooded [i], oviparous [i] vertebrate [i] animals characterized [i] ... 

s, is that water contains so little dissolved oxygen Oxygen

Oxygen is a chemical element [i] with the chemical symbol O and atomic number [i] 8.... 

 compared with atmospheric air. Air is around 21% O2; water typically is less than 0.001% dissolved oxygen.

The density of water also causes problems that increase dramatically with depth. The air pressure Atmospheric pressure

Atmospheric pressure is the pressure [i] above any area in the Earth's atmosphere [i] caused by the weight [i] ... 

 at the planet surface is 101 kilopascals . A comparable water pressure occurs at a depth of only 10 m Thus, at about 10 m below the surface the water exerts twice the pressure on the body as air at surface level.

For solid objects like our bones and muscles, this added pressure is not much of a problem; but it is a problem for any air-filled spaces like the mouth Mouth

The mouth, also known as the buccal cavity or the oral cavity, is the opening through which ... 

, ear Ear

The ear is the sense organ [i] that detects sound. ... 

s, paranasal sinuses and lungs. This is because the air in those spaces reduces in volume when under pressure and so does not provide those spaces with support from the higher outside pressure. Even at a depth of 8 feet underwater, an inability to equalize air pressure in the middle ear with outside water pressure can cause pain, and the tympanic membrane can rupture at depths under 10 ft . The danger of pressure damage is greatest in shallow water because the rate of pressure change is greatest at the surface of the water. For example the pressure increase between the surface and 10 m is 100% , but the pressure increase from 30 m to 40 m is only 25% .

Any object immersed in water is provided with a buoyant Buoyancy

In physics [i], buoyancy is an upward force [i] on an object immersed in a fluid [i], enabling it to flo ... 

 force that counters the force of gravity Gravitation

In physics [i], gravitation or gravity is the tendency of objects with mass [i] to accelerate [i] ... 

, appearing to make the object less heavy. If the overall density of the object exceeds the density of water, the object sinks. If the overall density is less than the density of water, the object rises until it floats on the surface.


With increasing depth underwater, sunlight Sunlight

Sunlight in the broad sense is the total spectrum [i] of electromagnetic radiation [i] give ... 

 is absorbed, and the amount of visible light Light

Light is electromagnetic radiation [i] with a wavelength [i] that is visible to the eye [i] or, in a technical [i] ... 

 diminishes. Because absorption is greater for long wavelength Wavelength

The wavelength is the distance between repeating units of a wave [i] pattern. ... 

s than for short wavelengths , the colour spectrum Visible spectrum

The visible spectrum is the portion of the electromagnetic spectrum [i] that is visible [i] ... 

 is rapidly altered with increasing depth. White objects at the surface appear bluish underwater, and red objects appear dark, even black. Although light penetration will be less if water is turbid Turbidity

Turbidity is a cloudiness or haziness of water caused by individual particles that are too small to be s... 

, in the very clear water of the open ocean less than 25% of the surface light reaches a depth of 10 m . At 100 m the light present from the sun is about 0.5% of that at the surface.

The euphotic depth is the depth at which light intensity falls to 1% of the value at the surface. This depth is dependent upon water clarity, being only a few meters underwater in a turbid estuary, but may reach 200 meters in the open ocean. At the euphotic depth, plants have no net energy gain from photosynthesis and thus cannot grow.

At depths greater than a few hundred meters, the sun has little effect on water temperature, because the sun's energy has been absorbed by water at the surface. In the great depths of the ocean the water temperature is very cold. In fact, 75% of the water in the world ocean has a temperature between 0 °C and 2 °C.

Water conducts heat around twenty five times more efficiently than air. Hypothermia, a potentially fatal condition, occurs when the human body's core temperature falls below 35 °C. Insulating the body's warmth from water is the main purpose of diving suit Diving suit

A diving suit is a garment or device designed to protect a diver [i] from the underwater [i] envi... 

s and exposure suits when used in water temperatures below 25 °C.

Sound Sound

Sound is a disturbance of mechanical energy [i] that propagates through matter [i] as a wave [i]. ... 

 is transmitted about four times faster in water than it is in air . The human brain can determine the direction of sound in air by detecting small differences in the time it takes for sound waves in air to reach each of the two ears. For these reasons divers find it difficult to determine the direction of sound underwater.

See also

  • Timeline of underwater technology

References

  • Dueker, C. W. 1970, Medical aspects of sport diving. A.S. Barnes and Co., New York. 232 pp.
  • – Oceanography notes at San Jose State University.