Alex Thomson, an algal ecologist with the Scottish Association for Marine Science, had planned to study coastal blooms of microalgae during his 2023 trip to Robert Island in Antarctica. But after arriving, he and his colleagues made a discovery that would change their mission.
Scientists have known for years that ice in the Arctic is teeming with microscopic algae. But aside from a few scattered observations, nobody knew whether such blooms were widespread in Antarctica’s ice caps (an ice cap is a type of gently domed glacier flowing outward in all directions). Thomson and his colleagues decided to collect a few samples from the Robert Island ice cap while they were there.
When they got the samples under a microscope, it was clear that the ice was a bustling hub of algal activity. “As we started to uncover this during the field season, we shifted our focus and took what was happening on the ice cap more seriously,” Thomson said.
In a study published in Nature Communications, the researchers revealed the extent and diversity of algae they found inhabiting the ice. Their findings warn that algae, whose pigments absorb heat from the Sun, may be accelerating the melting of Antarctic ice at a rate greater than previously thought.
“It’s the first paper quantifying that process in Antarctica,” said Alexandre Anesio, an Arctic algae expert at Aarhus University in Denmark who wasn’t involved in the new study.
Widespread Blooms and Unexpected Diversity
Scientists sampled from 198 locations and examined WorldView-2 satellite images from February 2023, which revealed darkened patches of ice indicative of algal blooms. On the basis of their sampling and the satellite images, the scientists estimated that algal blooms covered around 20% of the ice cap’s surface.
The newly discovered algal communities may represent one of the largest photosynthetic habitats in Antarctica. Researchers had previously estimated that all detectable photosynthetic life in Antarctica covered approximately 44 square kilometers. The ice cap algal blooms on Robert Island alone were equivalent to about 6% of that area.
“We were seeing this huge morphological diversity, loads of forms of Ancylonema that I’d never seen described in any of the literature.”
The scientists also found a diverse range of species in their samples. The most prevalent genus of ice algae, Ancylonema, has an elongated “sausage shape and can form in chains,” Thomson said. “We were seeing this huge morphological diversity, loads of forms of Ancylonema that I’d never seen described in any of the literature.”
Genetic analysis revealed that the Antarctic ice cap contains Ancylonema species that are similar to those found in the Arctic, but also others that were distinct. Some genetic lineages appear unique to Antarctica, suggesting that these communities may have evolved in isolation over millions of years.
Dark Pigments Accelerate Antarctic Ice Melt
Thomson was excited by the diversity of algae, but said the finding could have troubling implications.
When a researcher on the team used a backpack device that Thomson said “looks a bit like a piece of Ghostbusters apparatus” to measure how much light reflected off the ice’s surface, they discovered that areas of ice containing algae reflect significantly less light than areas without algae. The purple pigment within Ancylonema, which it uses as sunscreen to protect itself from ultraviolet radiation, absorbs more energy and heats the surrounding ice.
“This study gives a big preview of what can happen in Antarctica if you start to have warm summers.”
Through modeling, they found that algae can contribute up to around 2% of the total daily melting on the ice cap. Though the figure isn’t as high as it is in Greenland, where dense blooms can increase melt rates of the ice surface by 13%, scientists are concerned that warmer temperatures may allow more algae to grow, which would cause more heat to be absorbed into the ice caps. “That 2% is probably going to look more similar to Greenland” in the future, Anesio said.
Currently, climate models do not account for microorganisms’ contributions to melting. To Anesio and Thomson, studies like this highlight why that needs to change. “This study gives a big preview of what can happen in Antarctica if you start to have warm summers,” Anesio said.
—Andrew Chapman (@andrewchapman.bsky.social), Science Writer
