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August 2, 2021
Microscopic life is melting Greenland's ice sheet

Microscopic life is melting Greenland’s ice sheet

“Until recently people have thought of glaciers and ice sheets … as being relatively lifeless places,” says Cook, a British glaciologist. “But when you look under a microscope, the Greenland ice sheet in particular, and other glaciers, reveal themselves to be a frozen rainforest of biodiversity.”

The rainbow hues Cook encountered are created by an array of tiny life forms that thrive on the surface of the ice sheet.

Biodiversity is usually considered a good thing, but in this case the profusion of microbial life is speeding up ice melt, and likely causing global sea levels to rise faster than scientists have predicted.

Three times the size of Texas, the Greenland ice sheet covers around 656,000 square miles. A vast repository of fresh water, it is the largest single contributor to global sea level rise, and has the potential to increase ocean levels by up to seven meters (23 feet).
A recent study suggests the ice melt — accelerated by the climate crisis — may have already reached a point of no return.

Cook says the microscopic life forms he studies are contributing to the problem.

One of these organisms is an algae that grows in the thin layer of water on the surface of the ice. It produces a purple-brown pigment which acts “like a natural sunscreen,” says Cook, protecting the algae from the full force of the Arctic sunlight. The pigment also causes the ice to heat up and melt.

“If you go out on a hot day wearing a black t-shirt, you get warmer than if you go out on a hot day wearing a white t-shirt. The same thing happens on the ice,” says Cook. “These algae, like the black t-shirt for the glacier, are causing it to warm up in the sun and melt faster.”

Cook’s research on a part of the Greenland ice sheet spanning 3,900 square miles revealed that algae is responsible for up to 13% of the ice melt. In some localized areas, the algae accelerated melting by up to 26%.

“Vicious feedback cycle”

Glacier algae are not a new phenomenon — there are records of them in the diaries of polar explorers from the 1870s, says Cook. What has changed is global warming. With higher temperatures and reduced snow fall, a greater surface area of ice is exposed, allowing the algae to flourish.

The spreading algae boosts ice melt, releasing more water and nutrients held in the ice, which in turn promotes algae growth — a process Cook describes as a “vicious feedback cycle.”

And this is not the only destructive cycle taking place on the ice. Another microbe — a type of bacteria found on the surface of ice sheets and glaciers — glues dust particles in meltwater together, forming a dark, dense, soil-like substance called cryoconite. Ice underneath the cryoconite melts, creating pits on the surface of the ice sheet.

“That process creates an ecosystem, a niche on the ice surface that wouldn’t otherwise exist,” says Cook. The melt holes catch more dust, creating more cryoconite, which leads to more ice melt.

Melt holes caused by bacteria are another threat to Greenland's ice sheet. The largest of these is approximately 20 inches in diameter.

Mounting evidence of rapid ice melt

Cook’s research adds to a growing body of evidence that ice sheet melt rates have been underestimated. A recent study using satellite data found glaciers are more sensitive to a warming climate than previously thought. It showed the Greenland ice sheet is melting seven times faster now than it was in the 1990s.
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Previous estimates of sea level rise may have been too low partly because of a lack of information about the role of ice-loving microbes, says Cook.

Accurate predictions are essential, because even a small rise in sea level can have a big impact — threatening coastlines from the Pacific to Miami to India.
Sea level rise could cost the global economy $14.2 trillion in lost or damaged assets by the end of the century and expose up to 287 million people to episodic coastal flooding.

“If we want to make good decisions about how to manage our land, our infrastructure … and our economy into the future, we have to have good projections of sea level rise and the associated risks in that same time span,” Cook says.

What’s becoming clear is that ice sheets are surprisingly dynamic and complex environments. “There are so many questions to answer,” says Cook. “It’s kind of like a theme park for a scientist because there’s just so much to do.”