Snow isn’t all white: How ice crystals and algae can cause it to look red and blue

[Argentine, Canada, USA] What colour is snow? At first, it seems like an easy answer. Anyone who has seen snow will know it is white, the reason being because it reflects almost all visible light incident upon it.

But if you’ve ever dug a deep hole in snow and looked down, you will have noticed that sometimes it can actually appear blue – and sometimes even red, in other circumstances – but why?

Other objects appear different colours because they absorb certain wavelengths of visible light but reflect others – a green apple, for instance, reflects only mostly the green wavelength.

But, as reported by JSTOR, when snow is deep enough it can actually appear blue.

The reason for this is due to ice crystals in the snow, according to the National Snow and Ice Data Centre (NSIDC)

‘As light waves travel into the snow or ice, the ice grains scatter a large amount of light,’ the NSIDC explains.

While most of the light that is incident upon snow and ice is reflected, there is a very small tendency towards more red light being absorbed than blue, giving a slight bluish tint in deep snow and ice, such as this image from South Georgia Island in Antarctica
While most of the light that is incident upon snow and ice is reflected, there is a very small tendency towards more red light being absorbed than blue, giving a slight bluish tint in deep snow and ice, such as this image from South Georgia Island in Antarctica

While most of the light is reflected, there is a very small tendency towards more red light being absorbed than blue.

When you see just the surface of a pack of snow, the scattering of the blue light is almost completely impossible to notice.

But if you look into a significant amount of snow, about 3.3ft (one metre) or so, more photons emerge towards the blue end of the spectrum than the red end.

‘As light waves travel into the snow or ice, the ice grains scatter a large amount of light,’ the National Snow and Ice Data Centre (NSIDC) explains. Shown is a slight bluish tint in a melting glacier in East Greeland
‘As light waves travel into the snow or ice, the ice grains scatter a large amount of light,’ the National Snow and Ice Data Centre (NSIDC) explains. Shown is a slight bluish tint in a melting glacier in East Greeland

‘For instance, if you were to poke a hole in the snow and look down into the hole, you may see a bluish colour,’ said the NSIDC.

When snow appears red, though, it is for an entirely different reason.

This effect is due to cold-loving, fresh-water algae known as Chlamydomonas nivalis that contain a bright red pigment.

When snow appears red, though, it is for an entirely different reason. This effect is due to cold-loving, fresh-water algae known as Chlamydomonas nivalis (shown) that contain a bright red pigment.
When snow appears red, though, it is for an entirely different reason. This effect is due to cold-loving, fresh-water algae known as Chlamydomonas nivalis (shown) that contain a bright red pigment.

Also known as ‘watermelon snow’, it is ‘most common during the summertime in high alpine areas as well as along coastal polar regions’.

Interestingly, C. nivalis cells actually appear green under a microscope. The reason they appear pink in snow to our eyes is due to a biochemical called beta-carotene.

Also known as ‘watermelon snow’ , red snow is most common during the summertime in high alpine areas as well as along coastal polar regions. Shown is red snow in the Dolomites, Italy
Also known as ‘watermelon snow’ , red snow is most common during the summertime in high alpine areas as well as along coastal polar regions. Shown is red snow in the Dolomites, Italy

It protects the algae’s chlorophyll from the sun’s rays, but in the process gives them a red or pinkish hue, rather than green.

Be careful not to eat watermelon snow, though – it can act as a laxative.

The red colour doesnt always come from algae, however. Adelie penguins transiting to and from the sea shore colour the surface of the snow with whatever substance they drag with their feet. The pink colour here is from penguin poo, since they eat mostly krill, a small type of shrimp
The red colour doesnt always come from algae, however. Adelie penguins transiting to and from the sea shore colour the surface of the snow with whatever substance they drag with their feet. The pink colour here is from penguin poo, since they eat mostly krill, a small type of shrimp

Last year, meanwhile, a Washington photographer spent two month living in a remote base in Antarctica to reveal how the area can be surprisingly colourful.

Gaston Lacombe captured incredible images showing the bright pinks, greens and reds of the area – caused by everything from penguin poo to massive blooms of algae.

Red snow can also be caused by iron-rich seawater, such as Blood Falls in Antarctica’s Taylor Glacier, shown, where the water leaks from an ancient reservoir under the glacier. The iron oxidises when it comes into contact with the atmosphere, turning red
Red snow can also be caused by iron-rich seawater, such as Blood Falls in Antarctica’s Taylor Glacier, shown, where the water leaks from an ancient reservoir under the glacier. The iron oxidises when it comes into contact with the atmosphere, turning red

Mr Lacombe told MailOnline he was invited to the remote base by the Government of Argentina as its artist in residence.

Gaston Lacombe spent two months at Esperanza Base, a permanent research station on Antarctica’s Trinity Peninsula, to capture amazing images of coloured snow last year. Here, the red snow effect is caused by the algae Chlamydomonas nivalis
Gaston Lacombe spent two months at Esperanza Base, a permanent research station on Antarctica’s Trinity Peninsula, to capture amazing images of coloured snow last year. Here, the red snow effect is caused by the algae Chlamydomonas nivalis

The Canadian photographer now based in Washington, D.C. spent two months at Esperanza Base, a permanent research station on Antarctica’s Trinity Peninsula.

 

Photo: Dreaming of a white Christmas? Don’t dig too deep into snow, or you might start to notice a bluish tint. This is due to more and more of the ice crystals in the snow reflecting blue light, and absorbing other types, although of course in this image the effect is amplified by the shadows as well

View original article at: Snow isn’t all white: How ice crystals and algae can cause it to look red and blue

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