ZONING OF THE OCEANS
1. Penetration of sunrays
Sunlight entering the water may travel about 1,000 meters (3,280 feet) into the ocean under the right conditions, but there is rarely any significant light beyond 200 meters (656 feet).
The ocean is divided into three zones based on depth and light level. The upper 200 meters (656 feet) of the ocean is called the euphotic, or "sunlight," zone. This zone contains the vast majority of commercial fisheries and is home to many protected marine mammals and sea turtles. The epipelagic (euphotic) zone, also called the sunlit zone, receives enough sunlight to support photosynthesis. The temperatures in this zone range anywhere from 40 to −3 °C (104 to 27 °F). The epipelagic zone is the one closest to the surface and is the best lit. It extends to 200 metres and contains both phytoplankton and zooplankton that can support larger organisms like marine mammals and some types of fish. Past 200 metres, not enough light penetrates the water to support life, and no plant life exists.
Only a small amount of light penetrates beyond this depth.
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The zone between 200 meters (656 feet) and 1,000 meters (3,280 feet) is usually referred to as the “twilight” zone, but is officially the dysphotic zone. In this zone, the intensity of light rapidly dissipates as depth increases. Such a miniscule amount of light penetrates beyond a depth of 200 meters that photosynthesis is no longer possible. The mesopelagic (disphotic) zone, where only small amounts of light penetrate, lies below the epipelagic zone. This zone is often referred to at the Twilight Zone due to its scarce amount of light. Temperatures in the mesopelagic zone range from 5 to 4 °C (41 to 39 °F). The pressure is higher here, it can be up to 1,470 pounds per square inch (10,100,000 Pa) and increases with depth.
The aphotic, or “midnight,” zone exists in depths below 1,000 meters (3,280 feet). Sunlight does not penetrate to these depths and the zone is bathed in darkness. 90% of the ocean lies in the bathypelagic (aphotic) zone into which no light penetrates. This is also called the midnight zone. Water pressure is very intense and the temperatures are near freezing range 0 to 6 °C (32 to 43 °F). Due to the total darkness in the zones past the epipelagic zone, many organisms that survive in the deep oceans do not have eyes, and other organisms make their own light with bioluminescence. Often the light is blue green in colour, because many marine organisms are sensitive to blue light. Two chemicals, luciferin and luciferase that react with one another to create a soft glow. The process by which bioluminescence is created is very similar to what happens when a glow stick is broken. Deep-sea organisms use bioluminescence for everything from luring prey to navigation .
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Animals such as fishes, whales, and sharks are found in the oceanic zone. There are creatures however, which thrive around hydrothermal vents, or geysers located on the ocean floor that expel super heated water that is rich in minerals. These organisms feed off of chemosynthetic bacteria, which use the super heated water and chemicals from the hydrothermal vents to create energy in place of photosynthesis. The existence of these bacteria allow creatures like squids, hatchet fish, octopuses, tube worms, giant clams, spider crabs and other organisms to survive
‘Photic’ is a derivative of ‘photon,’ the word for a particle of light.
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