The light in the water is unlike any other location on the planet. It’s a world that’s noticeably different from the one we know on land, and one to which marine creatures, plants, and bacteria have adapted in astonishing ways. When light travels from air to water, it behaves extremely differently.
It travels across the vast abysses of an ocean devoid of solid surfaces. These and other variables come together to produce a habitat unlike any other on Earth.
The description of the ocean’s vertical zones of the water column in terms of how much light these zones get reflects the significance of light in the ocean. The water is separated into three zones: euphotic, dysphotic, and aphotic, which are called for the quantity of sunshine they get.
The euphotic zone is the top 200 meters (656 feet) of the ocean.
This zone is also known as the sunshine zone because sunlight penetrates there enough to allow the development of phytoplankton and/or macro algae (i.e., plants that require sunlight to create food and live), supplying the majority of ocean primary production (food) (or epipelagic zone).
Food drifts down from above, ranging from microscopic clumps of bacteria and dead algae to occasional bonanzas like a dead whale, and organisms in the zones below are reliant on it.
The dysphotic zone is defined as the region between 200 and 1,000 meters (656 and 3,280 ft). Light intensity in this zone, also known as the twilight zone (or mesopelagic zone), is substantially diminished as depth increases, hence light penetration is negligible.
he mesopelagic zone receives around 20% of primary output from the surface. As a result, the density or biomass of residents of the mesopelagic zone is lower than at the surface, and mesopelagic creatures have an unusual range of methods for finding food and avoiding becoming meals for other species.
The aphotic zone, which includes the midnight zone (or bathypelagic zone) between 1,000 and 4,000 meters (3,280 and 13,123 feet), the abyss (or abyssopelagic zone) between 4,000 and 6,000 meters (13,123 and 19,685 feet), and the hadal zone (or hadopelagic zone) 6,000 meters (19,685 feet) and deeper, is where sunlight does not penetrate the eternal darkness below 1,000 meters (3,280 feet At this depths, creatures provide the only light accessible.
Only around 5% of the primary output from the top reaches the ocean’s depths. Biomass is reduced when there is less food available. Large objects, such as dead sharks or whales, sometimes reach the seabed, although food is often rare.
With depth, the intensity of sunshine gradually diminishes. The intensity, or quantity of light, is affected by the depth of the water, as well as the hues of light that are visible underwater. Water absorbs more than half of the visible light energy in the first 10 meters.
Depending on the condition of the water, a certain portion of incoming light is reflected away as it reaches the ocean surface. Less light will be reflected if it is quiet and smooth. More light will be reflected if the water is agitated and there are numerous waves.
Although seawater absorbs light far more severely than air, visible light is composed of a rainbow of wavelengths, each of which we experience as a distinct hue. Blue light penetrates the waters more deeply (giving the ocean its distinctive color).
The ocean is quite deep, and light can only travel so far under the surface. The molecules in the water scatter and absorb the light energy as it moves through it. There is nothing to discern at high depths because light is so diffused.
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