A portion of the Greenland ice sheet. Image: Wikimedia Commons

The Greenland ice sheet is getting darker, and that’s bad news for the Arctic thermostat, since darker surfaces absorb more heat. Now, a pair of scientists have concluded that in at least one section of Greenland, tiny algae play an outsized role in giving the ice its surprising shade.

Every summer, a dark area appears along the western margin of the Greenland ice sheet. Folks have mainly attributed the discoloratoin to dust and black carbon, sooty stuff released from coal-fired power plants and during wildfires.

But ice-dwelling algae, which produce dark pigments to combat the fierce solar radiation on ice sheets, could also play a role. A study published last year in Nature Communications found that across the pan European Arctic, red snow algae are so effective at turning glaciers bubblegum pink that they’re causing them to melt faster. Marek Stibal, a microbial ecologist at Charles University in Prague, wondered if ice algae could be responsible for western Greenland’s discoloration, too.

Lo and behold, it seems they are. In research published recently in Geophysical Research Letters, Stibal, along with co-author Jason Box of The Geologic Survey of Denmark, present field measurements collected over two months in 2014 along the edge of the dark area at the southwest margin of the Greenland ice sheet. The researchers measured changes in surface reflectance, or albedo, as well as the abundance of ice algae and other albedo-reducing materials, like soot.

Overall, the researchers found that algae played a bigger role than non-living particles in reducing the ice’s albedo, and that their abundance could explain 70 percent of the variation in reflectance across the study area. As one of the first studies to quantify the role tiny critters play in discoloring the Greenland ice sheet, that’s kind of a big deal. “Algal growth is a crucial control of bare ice darkening,” the authors write.

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If the findings are borne out elsewhere, that would have a major implication: It would suggest that future melting on the Greenland ice sheet will be driven not just by rising temperatures, but by biology.

More algal growth—which could be triggered by melting ice (even ice algae need liquid water), and nutrient-laden dust—could result in a darker ice sheet, causing even more melting in the future. Basically, a vicious feedback loop. As a reminder, the Greenland ice sheet contains enough frozen water to raise global sea levels by nearly 25 feet. Feedback loops that cause ice to melt are generally bad for humans.

“Incorporating the darkening effect of algal growth is expected to improve future projections of the Greenland ice sheet melting,” the authors write.

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But Marco Tedesco, a Columbia University Earth scientist who led a study last year demonstrating that the entire Greenland ice sheet has been getting darker since the ‘90s, warns that we shouldn’t get too ahead of ourselves.

“I think the work is excellent,” Tedesco said of the new study. “It is very timely, and I think fascinating.”

But, he added, “it is basically one point, at one location that’s very specific. There is still a lot that needs to be done to quantify what is the role of these organisms,” across the entire ice sheet. “We need this work replicated.”

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Until that field replication arrives—and ideally, is complemented by satellite measurements of algae over broader scales—we’re left with the troubling possibility that ice-dwelling microbes are secretly plotting our demise. Honestly, it’s just the sort of weird thing that would screw us in the end.