Scientists drilling into a buried Antarctic lake 600 kilometres from the South Pole have found surprising signs of ancient life: the carcasses of tiny animals preserved under a kilometre of ice.
The crustaceans and a tardigrade, or ‘water bear’ — all smaller than poppy seeds — were found in Subglacial Lake Mercer, a body of water that had lain undisturbed for thousands of years. Until now, humans had seen the lake only indirectly, through ice-penetrating radar and other remote-sensing techniques. But that changed on 26 December when researchers funded by the US National Science Foundation (NSF) succeeded in melting a narrow portal through the ice to the water below.
Discovering the animals there was “fully unexpected”, says David Harwood, a micro-palaeontologist at the University of Nebraska-Lincoln who is part of the expedition — known as SALSA (Subglacial Antarctic Lakes Scientific Access).
The intrigue deepened when biologists realized that at least some of the beasts from Lake Mercer were landlubbers. The eight-legged tardigrade resembles species known to inhabit damp soils. What looked like worms were actually the tendrils of a land-dwelling plant or fungus. And although the scientists couldn’t rule out the possibility that the crustaceans had been ocean denizens, they might just as easily have come from small, ice-covered lakes.
The researchers now think that the creatures inhabited ponds and streams in the Transantarctic Mountains, roughly 50 kilometres from Lake Mercer, during brief warm periods in which the glaciers receded — either in the past 10,000 years, or 120,000 years ago. Later, as the climate cooled, ice smothered these oases of animal life. How the crustaceans and tardigrade reached Lake Mercer is still a matter of debate. Answers could come as the SALSA team tries to determine the age of the material using carbon dating and attempts to sequence the creatures’ DNA. Piecing together that history could reveal more about when, and how far, Antarctica’s glaciers retreated millennia ago.
“This is really cool,” says Slawek Tulaczyk, a glaciologist at the University of California, Santa Cruz, who is not part of the SALSA team. “It’s definitely surprising.” Tulaczyk, who has studied sediments retrieved from beneath glacial ice since the 1990s, says that nothing like that has ever been found before under the ice sheet. He was a co-leader of the only previous expedition to drill into a subglacial Antarctic lake — in 2013 at Lake Whillans, 50 kilometres from Lake Mercer. Scientists found Lake Whillans brimming with microbes, but saw no signs of higher life.