Glaciers' Unforeseen Foe: Algae

The algae invading glaciers protect themselves from sunlight by turning red, a process that can dramatically increase melting.
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(Photo: Martin St-Amant/Wikimedia Commons)

(Photo: Martin St-Amant/Wikimedia Commons)

The world's glaciers aren't just overheating, being coated with soot, and melting away. They're getting slimed.

Despite making up just one percent of the ice on the planet's surface, glaciers, which are frozen rivers found on mountaintops and in polar regions, are melting so rapidly their decline is blamed for nearly a third of global sea-level rise. And as the hard ice on their surfaces warms and turns into slush, algae are moving in.

Like soot, algae on the surface of a glacier can speed up its melting. Dark materials reduce the snowpack's reflectiveness, or albedo, meaning the glacier absorbs energy-rich sunlight instead of bouncing it back into space.

"With more melting," says Liane Benning, a biogeochemistry professor at the University of Leeds, "there will be more biology."

After producing sunlight-consuming chlorophyll during the spring, the algae must protect themselves from UV rays. So they produce caretenoid compounds. These red compounds act like sunscreen, absorbing energy and softening the ultraviolet blow.

The algae that grow on snow and ice are not your garden-variety plankton. They have adapted to high UV-radiation and nutrient-poor conditions. And newly published research led by Benning warns that glacier-dwelling algae are equipped with a special adaptation that's further accelerating glaciers' demise.

Gelid alga turns blood red.

After producing sunlight-consuming chlorophyll during the spring, the algae must protect themselves from UV rays. So they produce caretenoid compounds. These red compounds act like sunscreen, absorbing energy and softening the ultraviolet blow to green chlorophyll cells. In absorbing that excess energy, the red cells further drive down the albedo of the colonized snow and ice.

Benning and other researchers sampled microbial habitats of Greenland's Mittivakkat glacier during three weeks in the summer of 2012—a summer that was plagued by near-record breaking heat and melting throughout the icy country. The team reported last week in FEMS Microbiology Ecology that on July 6 of that year the glacier was "fully snow-covered"—as white as cotton wool. Just two days later, as rising temperatures triggered the start of what would become an epic melt, two visibly green patches of snow had appeared at the bottom of the glacier. Two days after that, several thin layers of red snow were found next to the green patches. During the following two weeks, "numerous" patches appeared on the glacier and quickly changed from light to dark red snow. Sometimes during the summer as much as half of the one-square-kilometer sampled area was covered by a layer of red snow between one and two millimeters thick. By July 25, more than two-thirds of the glacier had lost its snow and was covered with gray ice colonized by algae and sullied in part by soot and other windblown pollution.

More research is needed to quantify the melt-inducing effects of the algae, but this pioneering study suggests that it could be significant—and it's not currently being considered in climate models.

"A decreased albedo may have positive feedbacks on the algae community," the scientists wrote in their paper. "During the time of observation, the development of [algae] pigmentation was not the sole cause of the observed darkening of the glacial surface although we hypothesize here it was likely the most dramatic."

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