Antarctica is being colonised by a mysterious algae that has turned the snow blood red.
Experts have shared these remarkable pictures of "watermelon snow" near a former British research station.
The toxic cold-loving Chlamydomonas nivalis is the snow equivalent of regular algae found in rivers but has spores that produce a unique red pigment that acts like a natural sunscreen.
The microscopic organisms have been found in snowfields across the world for thousands of years, lying dormant in the snow during the winter.
When the snow melts in the summer, the spores are exposed to sunlight and start growing.
The pictures were taken at the former British Faraday Station which was sold to Ukraine for a token £1 in 1996.
It is now known as Vernadsky Station and the blood-coloured snow was revealed by Ukraine's ministry of science and education.
The research team, based on Galindez Island, part of the Argentine Islands, said: “Such snow contributes to climate change, because the red-raspberry colour snow reflects less sunlight and melts faster.
“As a result, more and more bright algae are formed in the snow."
The algae's red pigment helps capture sunlight to further warm the snow, sometimes causing an "algal bloom" colouring the snow and nearby streams red.
The single-celled organisms can also appear in different colours – including green and more rarely orange.
They reportedly give off a faint watermelon smell but scientists don't know why.
Dr Stefanie Lutz, a geobiologist at GFZ German Research Center for Geosciences, has warned the little-understood algae could cause snow to reflect 13% less sunlight.
She said in a study published in Nature Communications that "little is known about the diversity or function of snow algae, nor their global effect on albedo (reflectivity) and hence glacial melting.
"This is despite the fact that coloured snow algal blooms have been known since Aristotle, and that they dominate primary production on snow and ice fields.
"We have recently shown that snow algae are critical players in glacial surface habitats and the dominating biomass immediately after the onset of melting.
"Snow algae are prolific primary colonisers and producers that can form extensive blooms in spring and summer."
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She added: "Our data show that the overall decrease in snow albedo by red pigmented snow algal blooms over an entire melt season can be 13%, likely leading to earlier exposure of dirty ice with an even lower surface albedo culminating in a further increase in melt rates.
"Our work paves the way for a universal model of algal–albedo interaction and a quantification of additional melting caused by algal blooms to be included in future climate models."
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