Deakin Communicating Science 2016

EES 200/101

50 Shades of Blue

(Wallpaper Abyss, 2016)

Winter is coming! I’m sure most of us would rather be going for a dip in a blue sandy beach somewhere, just soaking up some sun light than showing up for uni.

Have you ever stopped to wonder why these oceans are blue?

The water reflecting the colour of the sky is probably what you thought to be the reason behind its blue colour appearance? Well, think again!

 How do we see colour?

White light is a combination of the 7 colours in the rainbow. What primarily occurs is that the object will absorb some colours and reflect the remainder of the colours which will be detected by our eyes thus giving the object that particular colour that was reflected.

For example, an apple appears red as it absorbs all colours of the spectrum except red.

Now, back to why the oceans are blue…                       (, 2016)

Ocean water is clear but the absorption and scattering of light is the major determinant of ocean colour. Similar to the apple scenario in the example above, the ocean reflects blue wavelengths of light. However absorption is a much larger factor than the scattering of light when it comes to ocean waters.

The ocean rapidly absorbs red light and has weak absorption of blue light. Much of the sunlight that hits the water is reflected back directly but most of it is able to penetrate the ocean surface and interact with water molecules that it comes across.

Nearly all the sunlight that enters the ocean is absorbed apart from the regions close to the coast.

Water absorbs red, yellow and green wavelengths of light while reflecting light of shorter wavelength such as blue and violet.

The scattering of light is also affected by any particles suspended in the water. Run off from rivers, re-suspension of sand, silt from the bottom by tides, waves and storms and several other substances are capable of altering the colour of near-shore waters.

The wavelengths of light absorbed can vary according to the types of particles present like phytoplankton.

Phytoplankton uses chlorophyll which is considered to be the most important light-absorbing substance in the oceans, to produce carbon via photosynthesis.

Chlorophyll is a green pigment and phytoplankton preferentially absorbs red and blue light while reflecting green portions of the spectrum as a consequence. Hence areas with higher density of phytoplankton will appear as shades of blue-green/green.

Resources: (2016). In the eye | Causes of Color. [online] Available at: [Accessed 7 May 2016].

Science, L. (2010). How Do We See Color?. [online] Live Science. Available at: [Accessed 7 May 2016]. (2016). Ocean Color – NASA Science. [online] Available at: [Accessed 7 May 2016].

Wallpaper Abyss. (2016). Mother nature at her best Computer Wallpapers, Desktop Backgrounds | 1920×1080 | ID:292379. [online] Available at: [Accessed 7 May 2016]. (2016). DayGlo | Fluorescent Color Theory. [online] Available at: [Accessed 7 May 2016].










3 comments on “50 Shades of Blue

  1. demagi
    May 8, 2016

    This article is actually interesting because we have always wondered why the sky is blue but haven’t really given much thought to the ocean. The physics side i.e reflection is well explained. It’s a little known fact that phytoplankton contribute to the colour of the ocean. You have explained well on how the phytoplankton absorbs different wavelengths and gives out different colours.
    Another factor that contributes to colour is the depth. If the depth of water decreases, the light can penetrate all the way through.


  2. kanan
    May 8, 2016

    When I was 10 years old, I read a book about why sky is blue and I thought ocean would be same reason. But I didn’t know about phytoplankton in the sea also absorb light waves! I was surprised.
    You mention reflection of light causes blue color of the oceans and >demagi says depth is also associated.
    One more thing that the ocean becomes blue is “light scattering”, it is called “Rayleigh scattering.” This web site might be help

    So I think there are 3 reason, reflection, depth and light scattering make the ocean become blue.


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This entry was posted on May 8, 2016 by in Burwood - Friday 10am and tagged , .

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