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Microbes that feast on crushed rocks thrive in Antarctica's ice-covered lakes

Microbes living in an ice-covered lake in Antarctica are feasting on crushed rocks, researchers have discovered. And the little critters are thriving.

Subglacial lakes are bodies of freshwater, a majority of which are found in Antarctica, trapped between Earth's crust, or bedrock, and thick sheets of ice — sometimes several miles thick. These lakes are teeming with diverse microbes that feed off nutrients in the water. However, until now researchers were unsure exactly where these nutrients came from.

Subglacial lakes naturally erode over time as their water levels rise and fall. In a new study, researchers replicated this erosion in the lab by crushing up sediment samples taken from Lake Whillans — a 23-square-mile (60 square kilometers) subglacial lake buried beneath 2,600 feet (800 meters) of ice in Antarctica — and revealed how vital chemicals needed to sustain microbial communities are created.

Related: See photos of this Antarctica subglacial lake

"Our study is completely different to any previous studies on subglacial lakes," lead author Beatriz Gill Olivas, a glaciologist at the University of Bristol in the U.K., told Live Science. "Prior studies have looked at how erosion of bedrock could produce gases in subglacial environments, but our study went further by looking at how erosion could also release biologically important nutrient sources to the water."

The finding could have "exciting implications" for studying how microbial life might develop elsewhere in the universe, she added.

Crushing sediment

Lake Whillans undergoes periods of filling and draining. When full, it is known as a high stand, and when it drains the lake is considered a low stand. The difference in depth between high and low stands in Lake Whillans is only around 13 feet (4 meters): High stands reach 39 feet (12 m) depth, dropping to a depth of 26 feet (8 m) at low stands. But at low stand, the ice stream — a corridor of fast flow within the ice sheet— comes into direct contact with large areas of the lake, Gill Olivas said."Therefore, you might expect to see some erosion," she added.

Lake Whillans is also part of a larger hydrological system, and erosion occuring in connected areas could feed chemicals into the larger lake, Gill Olivas said.

Researchers replicated this erosion in the lab by crushing up sediment samples from Lake Whillans and leaving them in water at 32 degrees Fahrenheit (0 degrees Celsius) with no oxygen, mimicking the conditions found within the lake.

Researchers analyzed sediment samples that were obtained from the Whillans Ice Stream Subglacial Access Research Drilling project. Scientists used a hot water drill to create a borehole through the thick ice sheet before collecting samples with a sterilized corer.

Releasing chemicals

The researchers left the crushed rocks submerged for over 40 days and then analyzed the water to see which chemicals had been released from the sediment. They found a wide variety of different chemicals including hydrogen, methane, carbon dioxide and ammonium.

Most of these chemicals are released instantly from the sediment as it is crushed.

"During crushing, the sediments get broken down into much smaller particles," Gill Olivas said. "As a result of this, microscopic bubbles found in minerals, known as fluid inclusions, can be cracked open, to release gases and liquid that were previously trapped in these bubbles."

Gases trapped between individual grains of sediment are also released into the water, she added.

However, others were created over time as certain minerals dissolved or reacted with other molecules in the water.

Microbial communities

One group of microbes, known as methanotrophs, feed off methane to create energy to grow. The opposite happens in methanogens, which create energy by converting hydrogen and carbon dioxide into methane. The lake also harbors specialized bacteria that get their energy by converting ammonium to nitrite and then into nitrate, a process known as nitrification.

A lot of the compounds created in subglacial lakes are also highly reducing or oxidizing, meaning they easily give and take electrons during chemical reactions, which also creates what is known as a redox gradient in the lake. This gradient helps recycle elements that are capable of having multiple oxidation states, such as sulfur or iron, by easily allowing them to gain and lose electrons. Specialized microbes, known as chemolithotrophs, can catalyze the oxidation of these elements as a source of energy.

Basically, for every chemical present in the lake, researchers found a group of microbes that have evolved to exploit it for energy.

Extraterrestrial life

These findings could be helpful to researchers hunting for extraterrestrial life. Underground lakes and frozen oceans are thought to be common in the universe, even in our own solar system.

"Lakes in Antarctica can be a proxy for extreme environments in other planetary systems," Gill Olivas said. "They offer a great insight into how microbial life might survive in other environments."