Why does the ocean appear blue? Is it because of the sky’s reflection?

There are a lot of questions from our ever-curious brains about our vast world. The complex body processes. Nature’s way of making life unfathomable, creatures and species that co-exist with humans, or even some that were already there even before humanity inhabit the Earth, why the sea is salty, why the rainbows have different colors, how gravity works, and so on.

On our quest to answering life’s questions, we go to school, study, read books or ask Google. Why do you think the ocean appears to have a blue color? Is it due to the sky’s reflection? The quick answer is no. If you are on a plane, or on a parachute where you can have an overlook of the ocean’s vastness, you will notice that it has greenish to bluish hues. Pure water is crystal clear, but if there is a lot of water, and the water is profound that there are no reflections off the seafloor, the water appears as a very dark navy blue.

Based on NASA’s ocean color website, the color of the ocean can be determined by the interactions of incident light with substances or particles present in the water. Therefore, sunlight and the organisms present in a particular ocean affects its color and not the sky’s reflection.

The water molecules in the ocean mostly absorb the red, yellow, and green wavelengths of the sunlight, than the blue wavelengths, so it is reflected when the light hits the ocean.

Another influencing factor to the ocean’s color is the free-floating photosynthetic microorganisms called phytoplankton and the inorganic particulates. The chlorophyll in the phytoplankton contains green pigment, and absorbs blue and red wavelengths and transmits in the green. So the part of the ocean where these phytoplankton is mostly present, makes the ocean appear in the shades of blue-green to green, depending upon the type and density of the phytoplankton population there. Therefore he more phytoplankton in the water, the greener it is, and the lesser phytoplankton, the bluer it is. (click here for more details)

Light is reflected and absorbed by the particulate matter, which reduces the clarity of the water. Dissolved Substances in water can also affect its color. Other substances usually composed of organic carbon may be found dissolved in the water, which can also absorb light. Researchers refer to these substances as colored dissolved organic matter or CDOM.

The suspension of the particles in the water increases the scattering of light. For example, in coastal areas, suspension of sand and silt from the bottom of the tides, runoff from rivers, waves, and storms and several other substances can change the color of the near-shore waters. Some types of particles like algae can also contain substances that absorb certain wavelengths of light, which adapts its appearance.

How about the other “colored” Seas?

The Red Sea

The Red Sea extending from Suez, Egypt to the Bab el-Mandeb Strait, is one of the saltiest and hottest seawater in the world. Its Greek name is Erythra Thalassa meaning red, but in Hebrew, it is called Yam Suph, or Sea of Reeds, most likely due to the reeds, and in Egypt, it is called “Green Space.” However, it was named the Red Sea due to the color changes observed in its waters. Usually, it has an intense blue-green color, but with the extensive blooms of the algae Trichodesmium erythraeum, which, upon dying off, turn the sea a reddish-brown color. The Red Sea connects to the ocean without even one river meets the sea. (click here for more details)

The Yellow Sea

The Yellow Sea is a semi-enclosed marginal sea off the east coast of Asia and to the west of the Korean Peninsula. Its high tides can reach about 10 meters high. One explanation and a possible reason for its name is its distinctive brownish yellow color. Its water comes from the Yellow River flow, containing huge amounts of silts from the upper plains. (click here for more details)

The White Sea

The White Sea is an inland sea found in the north of the European part of Russia belonging to the Arctic Ocean. For six to seven months every year, it is covered with ice.   There are two hypotheses on its name. One theory suggests that it’s called the White Sea because of its appearance covered by ice that makes it white. And the other theory says that the northern sky’s reflection to the sea makes it appear whitish.