Why is the sea always so blue?

The color of seawater is mainly caused by the optical properties of seawater, that is, the absorption, reflection and scattering of sunlight by seawater. We know that sunlight is composed of seven colors of red, orange, yellow, green, cyan, indigo, and violet light. The seven colors of light have different wavelengths, from red light to purple light, with longer and shorter wavelengths. Among them, red with the longer wavelength Light, orange light and yellow light have strong penetrating ability and are most easily absorbed by water molecules. Blue light and violet light with shorter wavelengths have weak penetrating capabilities and are most easily scattered and reflected when encountering pure seawater. And because people's eyes are very insensitive to purple light, they often turn a blind eye, but are more sensitive to blue light. As a result, the ocean we see appears azure or dark blue. If you take a bucket of seawater and place it in a bowl, the seawater will be colorless and transparent like ordinary water. In fact, the sea water does not all look blue, but red, yellow, white, black, etc., which are colorful. Because the color of seawater is not only affected by the above factors, but also affected by other factors such as suspended substances in the seawater, the depth of the seawater, clouds, etc. For example, the Yellow Sea in my country looks yellow-green. This is because a large amount of sediment carried by the Yellow River in ancient times "dyed" the sea water yellow. Although the Yellow River is now diverted and flows into the Bohai Sea, the northern part of the Yellow Sea is connected to it by the wide Bohai Strait, and it is also fed by rivers such as the Huaihe River, so the sea surface is still light yellow.

The Red Sea between Asia and Africa, because of its very high water temperature, grows a kind of algae in the sea, which turns reddish-brown after dying in large numbers, dyeing the seawater red. The Red Sea got its name from this.

As for the Black Sea, due to the injection of water from the Danube, Don, Dnieper and other rivers, the density of the surface layer is very small, while the density of the deep layer is very high due to the influence of the high salinity seawater of the Mediterranean Sea. In this way, the density of the upper layer is small and the density of the lower layer is high, and the difference is very large, making it difficult to exchange water bodies in the upper and lower layers. There is only a narrow and shallow Turkish Strait connecting the Black Sea and the Mediterranean Sea, making it difficult to exchange large amounts of seawater between them. In this way, the lower seawater of the Black Sea has been in an anoxic environment for a long time. The filth secreted by the organisms in the upper seawater and various animals and plants died and then sank to the depths to rot and smell. A large amount of sludge and turbid water turned the seawater black.

The Arctic Ocean penetrates deep into the White Sea in northern Russia. It is called the White Sea because it has a higher latitude, is cold all year round, has vast amounts of ice and snow, and has low organic content, so the water appears white.