“Snowflake, white skirt,” says a well-known children’s song. White is the color that everyone associates with snow – and therefore also with the region around the polar caps. The researchers in Antarctica were all the more surprised when they suddenly saw something completely different: poison green flakes.
Scientists from the British universities of Cambridge and Edinburgh now describe the unusual phenomenon in the journal “Nature Communications” – and provide an explanation: According to the climate change, algae spread that discolor the snow. The green swabs in the white snow landscape are likely to increase in the future.
Using satellite data and on-site surveys, the researchers had created a map that captured the current extent of the phenomenon on the Antarctic Peninsula. The snow covered with green algae is currently found mainly on the coast and close to penguin colonies and the nesting sites of other birds. With the warming, they would probably expand to higher, cooler areas, the researchers write.
Green algae are microscopic
“This is a major step forward in our understanding of Antarctic rural life and how it will change over the coming years as it warms up,” said Matt Davey of Cambridge University. “Snow algae are a key part of the continent’s capacity to extract carbon dioxide from the atmosphere through photosynthesis.”
Green algae grow both under and on the snow. They are microscopic, but if they occur in large enough numbers, they can discolor the snowy landscape. These color carpets sometimes extend over hundreds of square meters and are even visible from space. Red algal blooms have also been known for a long time in the Antarctic.
Davey’s team evaluated recordings of the Sentinel-2 satellites by the European space agency Esa, which were taken between 2017 and 2019. They also examined the spread of green snow at two locations on the Antarctic Peninsula, at Ryder Bay on the southeast coast of Adelaide Island and on the Fildes Peninsula, which is part of King George Island.
Algae store tons of carbon
“We identified 1679 single carpets of green algal blooms on the snow surface that together covered an area of 1.9 square kilometers,” said Davey. They would store around 479 tons of carbon in the summer growth season. This corresponds approximately to the amount that will be free with around 875,000 average car trips in Great Britain. The algae have grown where the temperature in summer remains above 0 degrees Celsius.
The spatial distribution of the algae was mainly due to the presence of seabirds and mammals, the excrement of which accelerates the growth of the algae as fertilizer. The scientists found 60 percent of the algal blooms within a 5-kilometer radius of a penguin colony. Algae also appeared frequently where seals come ashore and skua breed.
According to the researchers, around two thirds of the algae areas are on small, low-lying islands. The algae would probably disappear there if the climate warmed up further and the snow melted in the summer. Nevertheless, the scientists assume that the total amount of algae will increase in the coming years. The loss in the flat island regions is offset by the spread of the algae in higher, cooler areas.