Blood Falls in Antarctica is coloured by iron-rich minerals spilling out of the Taylor Glacier. (Benjamin Urmston/Associated Press)

Hidden in the bone-chilling dark beneath an Antarctic glacier, a colony of strange bacteria is thriving. Scientists investigating the flow of blood-red water from beneath the glacier discovered the bacteria, which have survived for millions of years, living on sulfur and iron compounds, they report in Friday's edition of the journal Science.

"Among the big questions here are: 'How does an ecosystem function below glaciers?' 'How are they able to persist below hundreds of metres of ice and live in permanently cold and dark conditions for extended periods of time, in the case of Blood Falls, over millions of years?" said lead researcher Jill Mikucki of Harvard University.

Blood Falls, flowing from beneath Taylor Glacier, has long evoked curiosity because of its colour. The researchers determined that iron compounds provide the colour, and in the process of their research they discovered bacteria in the water, an extremely salty pool.

John Priscu, of Montana State University, said that because the ecosystem has been isolated for so long in extreme conditions, it could help explain how life might exist on other planets, and serve as a model for how life can exist under ice.

The researchers believe the pool of water was trapped about 1.5 million years ago when the glacier moved over a lake. It doesn't freeze because it is four times saltier than the ocean.

The pool is so deep under the ice and so far back from the edge that the researchers couldn't drill down to it, but they were able to collect some of the outflow for testing.

"When I started running the chemical analysis on it, there was no oxygen," Mikucki said. "That was when this got really interesting, it was a real eureka moment."

Most of the bacteria she found were descended from marine micro-organisms — not from those found on land — and they were able to live without the food and light sources of the open ocean.

The researchers concluded that the ancestors of the bacteria probably lived in the ocean millions of years ago and when the Antarctic valleys rose a pool of seawater was trapped and was eventually capped by the flow of the glacier.

The Canadian Institute for Advanced Research, National Science Foundation, Harvard Microbial Sciences Initiative and the National Aeronautics and Space Administration funded the research.