Antarctic snow turns 'blood red'

What caused Antarctic snow to turn into such a chilling shade? This is the scientific explanation.

Andriy Zotov / Ministerio de Educación y Ciencia de Ucrania)

This time of year is summer in Antarctica, which means record temperature season (there has been a nine-day heat wave this month) and, unfortunately, also a time of glacial melting as a reminder of our changing climate. However, snow that seems to have been splashed with blood has appeared on the Antarctic Peninsula in recent weeks. What is this blood-red snow?

Researchers located at the Vernadsky Research Base of Ukraine (located on the island of Galindez, off the coast of the northernmost peninsula of Antarctica) observed that the ice around the base had shifted from the pristine white desert to being covered with what scientists know as "watermelon snow". The Ukrainian Ministry of Education and Science has published several photographs that perfectly illustrate this red and pink snow that seems to cut the edges of glaciers and even areas where reddish puddles appear on the icy plains.

What causes this watermelon snow?

Although we are shocked by the images, it is a common phenomenon in snow fields across the planet. So what is responsible for causing this “watermelon snow”? A toxic microscopic algae called Chlamydomonas nivalis that thrives in sub-zero temperatures. The germination of this algal colony is quite fast, so it spreads quickly. Algae produce spores that cope with low temperatures and stay alive in the snow. They love the cold and are the equivalent of algae that we can find in the rivers but with a different tonality.

Why does it look pink or red? This is due to the fact that in addition to the chlorophyll that we all know by its characteristic green colour, they have a reddish pigment (red carotene, astaxanthin) in their gelatinous wrap that serves as a shield for ultraviolet radiation and thus preserves the algae from genetic mutations. Microscopic organisms have been found in snow all over the planet for thousands of years; in fact, Aristotle himself wrote it down in the third century B.C. These algae remain dormant in snow during the winter but, when the climate warms up, as is the case right now with the Antarctic summer (between October and February), the spores are exposed to sunlight and begin to grow like flowers and produce this phenomenon worthy of a horror film. This is why the snow is dyed pink-reddish.

“This snow contributes to climate change, because raspberry-red snow reflects less sunlight and melts faster,” explains Ukrainian Ministry of Education and Science biologist Andriy Zotov. "As a result, more bright algae are formed in the snow". The more ice it melts, the faster the algae can spread. That, in turn, leads to more heating, more melting and more algal bloom.

Andriy Zotov / Ministerio de Educación y Ciencia de Ucrania)

When colder temperatures return with winter, algae shift into an inactive mode and the red dye disappears. This phenomenon can be observed in the Arctic, the Alps and other high mountain ecosystems.

Although we have seen this red and also pink snow, single-celled organisms can also appear in different colours, including green and, less frequently, orange. Everything seems to indicate that we’re probably going to see more events like this as the weather changes.

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