People often like to use blue to describe the ocean. In fact, the color of sea water ranges from dark blue to green, from yellowish to reddish brown, and even white, black, not just blue. It turns out that sea water, like ordinary water, is colorless and transparent. The color of the sea is determined by the optical properties of the sea water, the suspended matter in the sea water, the depth of the sea water, the characteristics of the clouds and other factors. As we all know, sunlight is composed of seven colors: red, orange, yellow, green, cyan, blue and purple. The wavelengths of these seven colors are different. From red light to purple light, the wavelengths gradually become shorter. Long wave has the strongest penetration ability and is most easily absorbed by water molecules. Short wave has weak penetration ability and is prone to reflection and scattering. The absorption, reflection and scattering of different wavelengths of light are also different. Red light, orange light and yellow light with longer light wave are absorbed gradually with the increase of ocean depth after they are shot into the sea.
Generally speaking, in the ocean with a depth of more than 100 meters, most of the light of these three wavelengths can be absorbed by the sea water, and can also increase the temperature of the sea water. The blue and purple light with shorter wavelength will have strong scattering and reflection when meeting with the purer sea water molecules, so the ocean people see will appear a blue or dark blue. Due to the increase of suspended matter, large particles, weak absorption of green light and strong scattering, the nearshore seawater is mostly light blue or green. The wavelength of purple light is the shortest and the reflection is the strongest. Why is the sea water not purple? Scientific experiments have proved that people's eyes are biased to a certain extent. People's eyes are very weak in the perception of purple light, so they are not sensitive to the purple reflected by sea water, so they turn a blind eye to it. On the contrary, people's eyes are more sensitive to blue and green light. The vast majority of the ocean is blue. If there is more suspended matter in the sea, or due to other reasons, the color of the sea will no longer be blue. For example, the Yellow Sea in China was the estuary of the Yellow River in ancient times. A large amount of sediment carried by the Yellow River flowed into the sea and dyed the blue water yellow.
Although the Yellow River is now pouring into the Bohai Sea, the Yellow Sea is connected with the Bohai Sea through the Bohai Strait in the north, and it has to bear the water from the Huaihe River, Guanhe River and other rivers, so the sea is still light yellow. In the northwest of the Indian Ocean, the Red Sea between Asia and Africa has the highest water temperature in the world. There is a kind of reddish brown seaweed growing in the sea. Because this kind of seaweed blooms all year round, the sea surface is dyed red, so the red sea gets its name. In the Gulf of California in the northeast of the Pacific Ocean, there are blood red algae in the south, and a large amount of red soil brought by the Colorado River in the rainy season in the north. The sea water is reddish brown, which is called Zhuhai. The white sea is the marginal sea of the Arctic Ocean. It is deep inland in Northwest Russia. The Arctic Circle passes through the white sea. Because of its high latitude, cold climate, ice and snow all year round, and low organic matter content, the white sea is white, so it is called "white sea". On the surface of the Black Sea, there are fresh water from Don river, Dnieper River and duoe River, and the density is low; on the deep layer of the Black Sea, there are high salt water from the Mediterranean, and the density is high.
A density leap layer is formed between the upper and lower seawater, which seriously hinders the water exchange between the upper and lower water layers. The black sea exchanges water with the Mediterranean through the Bosporus and Dardanelles. Because the Strait is narrow and shallow, which greatly limits the water exchange between the Black Sea and the Mediterranean Sea, there is a lack of oxygen in the deep layer of the Black Sea. The filth secreted by organisms in the upper layer of the sea and the dead bodies sink deep into the sea, rot and stink, and a large amount of muddy water makes the sea black. In addition, the Black Sea area is often cloudy and rainy, and storms are fierce, which adds to the feeling of darkness. Red tide can also make the color of sea water abnormal. Red tide is a kind of phenomenon that plankton suddenly and sharply propagate and gather together in local sea area. The color of red tide is various, which mainly depends on what kind of marine plankton causes red tide. The red tide caused by Noctiluca Noctiluca is pink or brick red, the red tide caused by some dinoflagellates is green or brown, and the red tide caused by some diatoms is yellowish brown or reddish brown. In addition, as the sun sometimes disappears in the clouds and sometimes shines through the clouds, the color of the ocean changes. The color of the ocean also depends on the height of the sun from the horizon.