A mundane Antarctic lake hides a unique fossilized ecosystem, some 3000 years old and sealed by a permanent layer of ice. Studies of the organisms that lived there--and may still--will provide insight into life during the ice ages and on other planets, scientists say.
Organisms in extreme environments have long intrigued scientists for what they might reveal about the evolution of life on Earth and elsewhere. Lakes on the McMurdo Peninsula, the largest glacier-free swath of Antarctica, are the best available model for frozen planets. While measuring the depth of a nearby lake in 1995, a research team including biogeochemist Peter Doran of the University of Illinois, Chicago, decided to survey 6.8-square-kilometer Lake Vida. Everyone assumed Vida was an unpretentious hunk of ice like its neighbors. But at a depth of 19 meters, the signal from their ground-penetrating radar was completely absorbed--an unmistakable signature of brine beneath the ice.
To find out the lake's age and how it formed, researchers took ice cores down to a depth of 16 meters. The lowest layer contained frozen microbes, most likely cyanobacteria. Despite their age of 2800 years, according to carbon-14 dating, the bugs grew when exposed to liquid water in the lab. That suggests the brine below the ice may harbor one of the coldest and most saline ecosystems on Earth.
As the team reports in the 16 December online issue of the Proceedings of the National Academy of Sciences, the liquid water below never freezes because its salt concentration of 24.5%--about seven times that of seawater--prevents ice crystal formation. Equipment difficulties kept the team from sampling the brine itself. But NASA, interested in the similarities of Vida's brine pool to possible microbial life on Mars or Jupiter's moon Europa, will support a return expedition in 2004.
It's too soon to say that the microorganisms found at 16 meters are in fact 2800 years old, since the ice could have melted and refrozen recently, says microbial ecologist Warwick Vincent of the University of Laval in Quebec City, Canada. Solid conclusions about the new ecosystem will have to wait until the liquid water is sampled. But "the information generated by the study is fascinating and it provides a tantalizing first look at what might lie beneath," he says. "It has implications for early environments on Earth ... and also the potential for telling us about refuges during prolonged freeze-ups."