The color of the sea changes depending on the quantity and type of particles suspended in the water, as well as the depth of the ocean. These factors influence how light is absorbed and reflected, thus altering the hue of the water.
The color of the sea mainly depends on how light interacts with water. When a light ray hits the surface of the water, certain colors are quickly absorbed, such as red and yellow, while blue penetrates deeper before being scattered in all directions. As a result, our eyes generally perceive the water as blue. However, this blue varies according to the angle of the sun and the amount of available light. For example, in the middle of the day with a high sun and clear water, the color leans towards a bright turquoise blue. In contrast, at sunrise or sunset, the low-angle light makes the sea darker, sometimes even grayish or silvery. Ultimately, it’s all about the interplay between light, absorption, and diffusion.
In the sea, there are many tiny microscopic creatures called plankton. Some, like phytoplankton, contain green pigments (a bit like land plants), which clearly change the color of the water by giving it greenish or blue-green hues. When there are a lot of them, they even create areas where the sea looks almost fluorescent; we call this algal blooms. These microorganisms absorb light, especially red and blue, and reflect green, which is why this particular color stands out distinctly. Other times, it’s tiny red or brown algae that transform an entire beach with reddish or brownish hues, making it seem like the water has taken on an unusual tint. In short, depending on which little creatures are hanging around, you’ll see noticeable changes in the sea’s color!
Depth significantly changes the color of the water, simply because light does not penetrate it fully. As you go deeper, warm colors (red, orange, yellow) gradually disappear due to their poor absorption by water molecules. The deeper you dive, the more blue dominates, as it is the most persistent color, the last to be completely absorbed. As a result, shallow areas, like lagoons or beaches, often display a beautiful turquoise, while offshore, where the bottom plunges, the sea takes on a deep dark blue, almost marine. The deeper you go, the darker it gets, and the fewer visible pigments there are. That's also why, at great depths, even in broad daylight, it feels like you're in the middle of the night.
The color of the sea can be directly influenced by the type of sediments present on the seabed. If the bottom is made of white or light sands, the water will appear turquoise or light blue, as these bottoms reflect sunlight well. In contrast, a dark bottom composed of volcanic rocks or organic materials will give the sea darker shades, deep blue or even grayish. When the water is loaded with fine particles like clay or mud, it temporarily takes on a murky and brownish appearance, reducing its transparency. This is common after a storm, a big wave, or near river mouths that carry a lot of materials from the surrounding land.
The color of the sky directly impacts that of the sea: when it is gray or overcast, the sea appears darker or duller, while a bright blue sky makes it look more vibrant and luminous. Thick clouds filter sunlight, thus reducing reflections and altering the perception of the marine hue. Strong winds, by creating waves and mixing the surface, can also affect our perception of colors by adding a whiter color associated with foam and turbulence. Finally, rain can have a similar effect by blurring the surface and decreasing transparency, resulting in a darker and less colorful sea.
Did you know that the paradise-like turquoise color of some tropical seas often comes from the reflection of sunlight on white sands and shallow depths rather than directly from the water?
Did you know that areas rich in phytoplankton can sometimes be seen from space as large green or bluish whirlpools in the ocean? NASA even uses these observations to study marine ecosystems.
Did you know that at significant depths, red light is absorbed first, which makes underwater red objects appear dark or black just a few meters below the surface?
Did you know that the area of the Bermuda Triangle does not actually show a color that is particularly different from the rest of the ocean? This popular myth is not based on any specific visual phenomenon.
No, these names do not always reflect the color of the water itself. The Red Sea gets its name from seasonal red algae or the coral formations around it. The Black Sea, on the other hand, may owe its name to the difficult navigation or frequent storms in the region rather than the actual color of its water.
The daily or seasonal variation in the color of the sea can be explained by several factors, such as the seasonal development of plankton (which can give the waters a greener hue), as well as the brightness of the sky, the weather, and the clarity of the atmosphere on that day.
No, pure water is generally colorless, but it slightly absorbs red light and reflects more blue wavelengths. Thus, a sufficiently large depth of pure water will naturally appear bluish to the human eye.
Yes, certain types of pollution such as chemical discharges, algae blooms related to excess fertilizers (called eutrophication), and the presence of plastic waste can significantly influence the perceived color, altering the light spectrum reflected by the water.
The color of the sea depends on several factors, including the depth of the water, the presence of microorganisms such as plankton, the reflection of the sky, suspended sediments, and the quantity and angle of sunlight. Thus, a shallow sea may appear turquoise, while a deep sea will generally be darker and bluish.
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