Pictures: Blood-red snow takes over Antarctica, here's why:

Pictures of blood-red snow in Antarctica have gone viral online. But what is causing the bizarre phenomenon?

Scientists working at the Vernadsky Research Base in Antarctica have been surrounded by what they call “raspberry snow”. Pictures were posted on Facebook by Ukraine’s Ministry of Education and Science and soon went viral online.

The phenomenon is caused by Chlamydomonas nivalis, a species of green algae containing a secondary red carotenoid pigment in addition to chlorophyll.

Unlike most species of fresh-water algae, Chlamydomonas nivalis is cryophilic, capable of growth and reproduction in low temperatures, and thrives in freezing water.

The algae begins to sprout and gets a brighter colour during warmer summer month in Antarctica, generally between October and February. When colder temperatures return in the winter, the algae becomes dormant and the red tint disappears.

Earlier this month, weather stations recorded the hottest temperature on record for Antarctica. It was reported that thermometers at the Esperanza Base on the northern tip of the Antarctic Peninsula reached 18.3°C on February 6.

The bizarre effect is often referred to as watermelon snow, snow algae, pink snow, red snow, or blood snow.