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The ambient pressure in water with a free surface is a combination of the hydrostatic pressure due to the weight of the water column and the atmospheric pressure on the free surface. This increases approximately linearly with depth. Since water is much denser than air, much greater changes in ambient pressure can be experienced under water.
The epipelagic zone, otherwise known as the sunlit zone or the euphotic zone, goes to a depth of about 200 meters (656 feet). It is the depth of water to which sunlight is able to penetrate. Although it is only 2 to 3 percent of the entire ocean, the epipelagic zone is home to a massive number of organisms. [3]
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 10,100 kilopascals (1,460 psi) and increases with depth. [1] 54% of the ocean lies in the Bathypelagic (aphotic) zone into which no light penetrates. This is also called the midnight zone and the deep ocean.
The outside water pressure increases with depth and so the stresses on the hull also increase with depth. Each 10 metres (33 ft) of depth puts another atmosphere (1 bar, 14.7 psi, 101 kPa) of pressure on the hull, so at 300 metres (1,000 ft), the hull is withstanding thirty standard atmospheres (30 bar; 440 psi; 3,000 kPa) of water pressure.
The pressure of seawater at a depth of 33 feet equals one atmosphere. The absolute pressure at 33 feet depth in sea water is the sum of atmospheric and hydrostatic pressure for that depth, and is 66 fsw, or two atmospheres absolute. For every additional 33 feet of depth, another atmosphere of pressure accumulates. [6]
The descent zone was defined as the part of the dive between the surface and first reaching 85% of the maximum depth. The bottom zone is the part of the dive deeper than 85% of maximum depth. The multilevel zone is ascent from 85% to 25% of maximum depth, and the decompression zone is less than 25% of maximum depth.
This is because the gas in those spaces is much more compressible than the solids and liquids, and reduces in volume much more when under pressure and so does not provide those spaces with support against the higher outside pressure. Even at a depth of 8 ft (2.4 m) underwater, an inability to equalize air pressure in the middle ear with outside ...
The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word abyss comes from the Greek word ἄβυσσος ( ábussos ), meaning "bottomless". [ 1 ] At depths of 4,000–6,000 m (13,000–20,000 ft), [ 2 ] this zone remains in perpetual darkness.