To mark European Maritime Day, we are celebrating our planet’s most precious resource by revealing one of its most fascinating secrets. Have you ever wondered why, whether we look at it from above or dive into it, the sea appears to us in such a deep, mesmerising blue?
No, it’s not just a reflection of the sky! The answer lies in a marvellous combination of physics and chemistry that takes place every second beneath the surface.
1. Water acts as a ‘filter’
Sunlight appears white, but it contains all the colours of the rainbow. When it enters the water, the H2O molecules almost immediately absorb the warmer colours with longer wavelengths (such as red and orange), converting them into heat within the first few metres. Blue light, on the other hand, persists and manages to travel to depths of over 100 metres!
2. The Great Bounce-Back Game
That blue light which manages to penetrate does not dissipate into the void: it strikes water molecules and tiny suspended particles, bouncing off in all directions (a phenomenon known as diffusion). Some of this light is reflected upwards, and it is precisely this light that our eyes capture.
3. Shades of Life
The sea is not a monochrome canvas. When it turns green, it is often telling us about life: it is a sign of the presence of phytoplankton and chlorophyll, the ocean’s invisible forest that produces over 50 per cent of the oxygen we breathe.
Would you like to learn more about ocean science?
Here are some authoritative sources from leading international research organisations:
To understand the optical physics of water, see NOAA: https://oceanservice.noaa.gov/facts/oceanblue.html
To find out how satellites study the health of the sea through colour, see NASA: https://science.nasa.gov/earth…/oceanography/ocean-color/
Caring for the sea means protecting its extraordinary complexity, from invisible molecules to the vast migratory routes that criss-cross it. Happy European Maritime Day to everyone!
