Why Is the Ocean Blue? 4 Astonishing Factors Affecting the Ocean’s Color

The ocean is associated with many things, whether, salt, air, crashing waves, or a relaxing atmosphere, but perhaps most of all, it is associated with the color blue. For a long time, people have been wondering why the ocean is blue and what determines the color of the ocean.

Is the reason for their blue tint just that they reflect the color of the sky, or is it a bit deeper than that?

We will uncover these recurring questions to develop an understanding of why the ocean is blue.

It’s Not Due to the Color of The Sky

You might have heard that the color of the ocean is just reflecting the color of the sky, and while this is true to a certain degree, it is not the actual answer to why the sea is blue.

From the coast, the sea does appear to change color when the sky is grey and overcast or when orange and pink hues glitter on the water during sunrise and sunset.

But this reflection only occurs on the surface. The depths of the ocean remain blue as far as eyes can see, or better said, as far as the light penetrates them.

It’s Due to The Way Water Absorbs Light

Water molecules are pretty good at absorbing light. However, different colors or, better said, light rays are absorbed in various degrees. Water sort of acts like a filter that gradually absorbs all the colors except for blue, so blue is the prominent color that is scattered back and reaches human eyes.

The real reason for the color of the ocean to appear blue lies in the way water interacts with light. Sunlight consists of all the colors of the visible light spectrum, from red to violet. However, each of these colors of the rainbow has a different wavelength, making them act differently. Focusing only on visible light, the colors in the red part of the light spectrum have longer wavelengths, with red light having the longest one. These colors are absorbed by the water the quickest.

The colors in the blue part of the spectrum have shorter wavelengths; therefore, they have more energy and can travel to greater depths. Violet light has the shortest wavelength; however, blue is the color the least absorbed by water.

While reds, oranges, yellows, and even violets and greens are, at different rates, absorbed by the ocean, blues (and sometimes greens) are scattered back, leaving them to be the only colors left for our eyes to see.

This is also why everything under water appears to have a blue tint and color of the ocean is blue. While close to the surface, you can still recognize all the colors; the deeper you go, the more certain colors begin to fade. For example, 30 meters underwater, a red swimsuit looks black because water absorbs all the red hues.

Why is the Ocean Different Shades of Blue?

Now we know why the color of the ocean is generally in the shades of blue or green, but what determines whether the water appears azure, turquoise, or brownish? Why does the sea have different shades in different areas?

Algae and Sediment

Perhaps the most surprising thing is that the color of the ocean is, to a large degree, affected by phytoplankton floating in the water. Cells of this microscopic algae actually contain a green pigment called chlorophyll. They use for photosynthesis which allows them to produce about half of the Earth’s oxygen.

Chlorophyll is more prone to absorbing red and blue light while reflecting back green. This means that waters rich in phytoplankton will appear to be a shade of green rather than blue.

The color of the ocean can also display green, red, or other hues when light reflects off floating sediments and particles in the water.

Typically the more algae there is, the greener the sea should look. But the exact hue and color of the ocean doesn’t only depend on the density but also on the type of phytoplankton in the area. Some algae blooms, also known as red tides, can even color the ocean red.

Scientists monitor phytoplankton blooms in order to better understand their impact, but it also helps them study and predict other environmental changes.

Sand and silt stirred by waves and storms, runoffs from rivers, and other floating marine sediment increase the reflection of light. The rays that bounce off of them are the longer wavelengths of light, making the color of the ocean look murky or muddy brown. The crystal-clear waters of the Caribbean often appear light green rather than blue, which you might assume is due to the cleanliness of the water. While cleaner water does play a role, the colors are largely influenced by the plant life in many Caribbean waters, which reflects more green light.

Depth and Seafloor

Depth also plays a role in the color of the ocean. Shallow areas inherently have less water and, therefore, fewer water molecules that can absorb and reflect light. This results in light being able to shine through the water and reach the sea floor.

It comes as no surprise that, particularly in shallow water areas, the sea floor affects the shade of the ocean. The sand, rocks, or corals on the bottom reflect light differently than water molecules.

When light penetrates water completely, like in a drinking glass or a very shallow body of water, we see water as colorless, as not enough photons are absorbed. When the sea is shallow, the light bounces off of the ocean floor or marine plants, and the color of the ocean tends to appear more turquoise or light blue if the seafloor consists of white sand, rocks, or plant life.

Areas with deeper water are typically navy blue because a large mass of water can absorb and scatter much more light and because there are no reflections off the ocean floor that could influence the sea color. Not to mention that no light penetrates below 3,280 feet (1000 m), and the ocean is entirely dark at this depth.

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