Call to Earth

A ‘frozen rainforest’ of microscopic life is melting Greenland’s ice sheet

Editor’s Note: Call to Earth is a CNN initiative in partnership with Rolex. Joseph Cook is a Rolex Awards Laureate.

CNN  — 

When Joseph Cook first landed on the Greenland ice sheet in 2010, he was expecting to see a pristine white environment. What he found was a “colorful patchwork” – from blacks and grays to greens, purples and browns, with neon blue melt streams cutting through the ice.

“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.”

British glaciologist Joseph Cook preparing equipment to test the "albedo" or reflectivity of Greenland's ice sheet.

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.

Algae acts like a black t-shirt

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.

Algae growing on the Greenland ice sheet is causing it to melt faster.
A 'frozen rainforest' of microscopic life is melting Greenland's ice sheet
03:30 - Source: CNN

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%.

Algae blooms around a field camp on Greenland's ice sheet, where Joseph Cook was based during a 2016 expedition.

‘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.