THE popular image of Antarctica as a frozen, almost lifeless desert needs a makeover. For the first time, water from a lake beneath the ice has been found to harbour a vibrant microbial ecosystem.
“Our discovery proves that water is habitable space, even if it’s at sub-zero temperatures and there is no sunlight,” says John Priscu of Montana State University in Bozeman. He co-led the US team that drilled into Lake Whillans, 800 metres beneath the west Antarctic ice sheet.
Water is habitable space, even if it’s at sub-zero temperatures and there is no sunlight
The finding is good news for astrobiologists hoping to discover life elsewhere in the solar system: in the ocean beneath the frozen surface of Jupiter’s moon Europa, for instance, or clinging on under the Martian polar ice caps.
Antarctica is home to about 400 subglacial lakes, many of which are linked in drainage basins. Priscu calls it “the planet’s largest wetland”.
Lake Whillans (see map) is one such lake. As it fills up with water from inland, the ice above swells. About every three years, the pressure builds up so much that water rushes out into the Southern Ocean, like fuel being siphoned from a car’s tank.
Priscu’s team broke into Lake Whillans in January 2013, using hot water to melt a 60-centimetre-diameter hole through the ice. The water used was kept sterile using filters, heating, ultraviolet light and hydrogen peroxide. That should lay to rest any suggestion that the microbes found were contaminants from the surface.
Such doubts have dogged claims about life in Lake Vostok in eastern Antartica. A Russian team took samples from the lake in 2012, but they used non-sterile kerosene as the drilling fluid.
In any case, the sheer numbers of microbes found in the samples from Lake Whillans argue against contamination. “We were surprised by the cell densities we observed,” says Priscu’s colleague Brent Christner of Louisiana State University in Baton Rouge. “They are very similar to what you’d find in low-nutrient lakes on the surface or in the open ocean.”
The team found almost 4000 species of single-celled organisms (Nature, DOI: 10.1038/nature13667). Most seem to be feeding on sediments on the lake bed, laid down when the area was last ice-free and under the ocean, at least 120,000 years ago.
Many of the microbes convert ammonium to nitrite. The most common species, accounting for about 13 per cent of the DNA sequences found, takes that nitrite and converts it to nitrate. Others seem to feed on methane.
Whillans is not necessarily representative of other subglacial lakes. For instance, Lake Vostok is thought to have been completely cut off, including from other lakes, for at least 15 million years. That means any microbes there may have to feed instead on chemicals released as bedrock is ground away by the surrounding ice. “What we have is one point on the map. We need more,” says Martin Siegert of Imperial College London.
“We’ve got to get down and sample these lakes,” says Priscu. But it will be hard to reach lakes nearer the centre of Antarctica, where conditions are harsher, without contaminating them with drilling fluid. Siegert heads a team that was thwarted in its 2012 efforts to reach Lake Ellsworth by boring through 3 km of ice. He hopes to try again in a few years.
Exploring beneath the ice of other bodies in our solar system will be an even tougher challenge. Still, finding a flourishing ecosystem beneath Antarctica boosts the idea that life may exist beyond Earth. “I believe the implications for life elsewhere in our solar system are significant,” says Edward Goolish of the NASA Ames Research Center in Mountain View, California.
This article appeared in print under the headline “Life thrives under Antarctica”
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