In an icy lake approximately 800 metres beneath the Antarctic ice sheet, scientists have discovered a diverse ecosystem of single-celled organisms that have managed to survive without ever seeing the light of the sun.
The discovery, reported Wednesday in the journal Nature, is not so much a surprise as a triumph of science and engineering. The research team spent 10 years and more than US$10 million to prove beyond a shadow of a doubt life did indeed exist in subglacial lakes near the South Pole.
"It's the real deal," said Peter Doran, an Earth scientist at the University of Illinois at Chicago, who was not involved in the study. "There was news that they found life early this year, but a bunch of us were waiting for the peer- reviewed paper to come out before we jumped for joy."
John Priscu, the lead scientist on the project, has been studying the Antarctic for 30 years. He published his first paper describing how life might exist in the extreme environment beneath the ice sheet in 1999 and has been looking for definitive proof ever since.
In the winter of 2013-14, he finally got his chance. After spending millions on a drill that could bore a clean hole free of contaminants through the ice sheet, and moving more than one million pounds of gear on giant sleds across the Antarctic ice sheet, he and his team had just four frenzied days to collect the water samples that would prove whether his theories were right or wrong.
Before claiming victory, he wanted to see three lines of evidence that life did exist in the underwater lake. He wanted to visually see the cells under a microscope, he wanted to prove they were alive by feeding them organic matter and measuring their respiration rate.
"I wasn't surprised to find life under there, but I was surprised how much life there was, and how they made a living," said Priscu, who teaches at Montana State University. "They are essentially eating the Earth."
Priscu and his team reported the discovery of nearly 4,000 species of microbes growing in the cold, dark environment of subglacial Lake Whillans in western Antarctica. There was about 130,000 cells in 1.2 millilitres of the tea-coloured lake water they brought to the surface, they write.
"I think we were all surprised by that number," said Brent Christner of Louisiana State University and the lead author of the Nature paper. "We've got lakes here on campus that we can take samples of, and the numbers are about in that range."
Life in the lakes of Louisiana has sunlight to provide it with energy, but in the lightless environment of subglacial Lake Whillans, the microbes rely on minerals from the bedrock and sediments. The pressure of the slowly moving ice above the lake grinds the underlying rock into a powder, liberating the minerals in the rock into the water and making them accessible to the microorganisms living there, said Christner. The microbes act on those iron, ammonium and sulphide compounds to create energy.
"Ice, water and rock is all that is really needed to fuel the system," he said.
The findings have major implications for the search for life outside of Earth, especially on the moons of Enceladus and Europa, where scientists believe a thick icy crust covers a vast, internal liquid ocean.
"Europa has an icy shelf and liquid water beneath it, just like we find in the Antarctic system, which allows us to draw some conclusions about what we might find there," said Priscu. "I'd love to be around when we finally penetrate that environment to look for life."
The researchers brought about 50 litres of the lake water back to the surface to study its chemistry and to see what might be living in it. The water was a brownish colour because of the very fine particles that were suspended in it.
Going forward, the researchers want to learn more about how nutrients created by microbial activity in Lake Whillans affect the water in the Indian Ocean. They would also like to look at other types of subglacial lakes in Antarctica, some of which are more than 900 metres deep and buried beneath more than three kilometres of ice.
"Now that we have shown that life can exist in this environment, we'd like to look at other lake types to see the biodiversity and ecosystems that exist under the ice, and get a better idea of their global importance," said Priscu, who was on his way to plan the next expedition.
The team is going back to Antarctica with its drill in November.
"Hopefully we'll have more discoveries coming soon," he said.
-- Los Angeles Times