Yes, it’s an obvious question “why is the ocean blue?”. Many people think that the blue color ocean is due to the reflection of blue light from the sky. Even I used to think the same for a quite long time. But this is not completely true while it contributes to a very small extent.
The ocean becomes blue by absorbing the light spectrum from sunlight; not reflecting it like the sky. The colors with low frequency / longer wavelengths are absorbed by water molecules first. So, Red, Orange, Yellow, and Green are absorbed quickly. The blue color penetrates deep into the ocean which causes the ocean to look blue.
Let’s dive into more details.
Why is the ocean blue?
As we know, the visible part of sunlight contains seven spectra of light (Violet, Indigo, Blue, Green, Yellow, Orange, and Red). Red light is having the highest wavelength (lowest frequency) of 720 nm whereas the wavelength of violet is the least with 380 nm.
If you pass light through a prism, you can see the light splits into 7 colors. This theory was demonstrated by Isaac Newton.
When the sunlight falls on the ocean, all the color spectrums penetrate into the water. The low-frequency colors are absorbed by water molecules quickly than the high-frequency colors. So, the Red, Orange, Yellow, and Green are absorbed in just a few meters. But, Blue color penetrates the most into the water, as a result, the ocean looks blue.
Then why do not violet and indigo cause water to be purple as they have an even higher frequency than blue? This is because the sunlight does not have enough amounts of these colors when it enters into the lower atmosphere. They are already absorbed and scattered on the upper atmosphere due to Rayleigh scattering effect.
More related to oceans can be found out here: National Oceanic and Atmospheric Administration (NOAA)
Why is the beach water green?
Phytoplankton (algae) is the most important factor in changing the watercolor to green. The chlorophyll present on the phytoplankton absorbs red and blue portions of the light, reflecting green as part of photosynthesis. So, the more the phytoplankton (algae) in water, the greener it looks.
In ocean/ seashores, the depth is less. So, part of green color also penetrates till the sea floor and reflects back which causes the beach water to look greenish blue.
What is the actual color of the ocean?
Pure water is colorless as it is made up of colorless gases hydrogen and oxygen. If we go deep into the ocean, the blue becomes darker and finally becomes completely dark. This is because blue light also gets absorbed slowly and no light can penetrate 3280 feet. The visible spectrum of sunlight can penetrate a maximum of 656 feet only.
Now, you can understand what color is the ocean beyond that, if there is no light.
In some cases, the water looks brown due to mud and pollution. You might have seen this in the case of rivers, ponds.
What color will be an object at the bottom of the ocean?
In the case of the deep ocean, water is completely dark and all the objects will look black due to lack of light. If you have a torch which can produce white light, you can see the real color of the object.
I hope the topic why is the ocean blue is helpful and can be easily understandable by kids as well. If you liked the post, please share with the ones who seek knowledge.