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The photic zone or euphotic zone (Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 'well lit') is the depth of the water in a lake
Lake

A lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all....
 or ocean
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
, that is exposed to sufficient sunlight
Sunlight

Sunlight, in the broad sense, is the total spectroscopy of the electromagnetic radiation given off by the Sun. On Earth, sunlight is Filter ed through the Earth's atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon....
 for photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
 to occur. The depth of the photic zone can be greatly affected by seasonal turbidity
Turbidity

Turbidity is the cloudiness or haze of a fluid caused by individual Particle that are generally invisible to the naked eye, similar to smoke in air....
. It extends from the atmosphere-water interface downwards to a depth where light intensity falls to 1% of that at the surface (also called euphotic depth), so its thickness depends on the extent of light attenuation
Attenuation

In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead....
 in the water column.






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The photic zone or euphotic zone (Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 'well lit') is the depth of the water in a lake
Lake

A lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all....
 or ocean
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
, that is exposed to sufficient sunlight
Sunlight

Sunlight, in the broad sense, is the total spectroscopy of the electromagnetic radiation given off by the Sun. On Earth, sunlight is Filter ed through the Earth's atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon....
 for photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
 to occur. The depth of the photic zone can be greatly affected by seasonal turbidity
Turbidity

Turbidity is the cloudiness or haze of a fluid caused by individual Particle that are generally invisible to the naked eye, similar to smoke in air....
. It extends from the atmosphere-water interface downwards to a depth where light intensity falls to 1% of that at the surface (also called euphotic depth), so its thickness depends on the extent of light attenuation
Attenuation

In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead....
 in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid
Turbidity

Turbidity is the cloudiness or haze of a fluid caused by individual Particle that are generally invisible to the naked eye, similar to smoke in air....
 eutrophic lakes, to around 200 metres in the open ocean. Since the photic zone is the only zone of water where primary productivity
Primary production

Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis, with chemosynthesis being much less important....
 occurs, an exception being the productivity connected with abyssal hydrothermal vent
Hydrothermal vent

A hydrothermal vent is a fissure vent in a planet's surface from which Geothermal heated water issues. Hydrothermal vents are commonly found near volcano active places, areas where tectonic plates are moving apart, ocean basins, and hotspot ....
s along mid-oceanic ridges
Mid-ocean ridge

A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics....
, the depth of the photic zone is generally proportional to the level of primary productivity that occurs in that area of the ocean. About 90% of all marine life lives in this region.

The transparency
Transparency (optics)

In optics, transparency is the material property of allowing light to pass through. In mineralogy, another term for this property is diaphaneity....
 of the water, which determines the depth of the photic zone, is simply measured with a Secchi disk
Secchi disk

The Secchi disk, created in 1865 by Angelo Secchi, is a circular disk used to measure water transparency in oceans and lakes. The disc is mounted on a pole or line, and lowered slowly down in the water....
.