Researchers at the University of Illinois at Chicago, writing in the Proceedings of the National Academy of Sciences, said the finding sheds light on the limits of life in extreme environments.
The brine has been isolated from the surface environment, and from any external sources of energy, for at least 2,800 years, they said.
"This provides us with new boundary conditions on the limits for life," researcher Peter Doran said. "The low temperature or high salinity on their own are limiting, but combined with an absence of solar energy or any new inputs from the atmosphere, they make this a very tough place to make a living."
The findings were unexpected because of the extremely salty, dark, cold, isolated ecosystem within the ice, scientists said.
The brine is oxygen-free, slightly acidic, and contains high levels of organic carbon and molecular hydrogen, the scientists said.
"Geochemical analyses suggest that chemical reactions between the brine and the underlying sediment generate nitrous oxide and molecular hydrogen," researcher Fabien Kenig said. "The hydrogen may provide some of the energy needed to support microbes."