A microbial ecosystem has been trapped under an Antarctic glacier for over a million years. Researchers have now figured out what fuels these bacteria thanks to a shift that has brought bright red, iron-rich ice to the surface.
The McMurdo Dry Valleys of Antarctica are considered one of the least hospitable places on Earth; NASA has used them to simulate conditions that might prevail on Mars. But scientists are now reporting the discovery of an ecosystem buried under the ice of one of these glaciers that stretches the definition of unusual well past the breaking point.
Nobody would be likely to suspect that there is any life underneath the ice, which is hundreds of meters thick in the area, if it weren’t for the striking red ice erupting from the glacier’s terminus, giving the formation the name Blood Falls. That red color comes from iron concentrated in the ice, which exists primarily in the Fe(II) state favored when oxygen is absent..
It seems that the red ice has travelled from a pocket that exists four kilometers from the glacier’s end, at a site where the ice is over 400m thick. Based on the chemical composition of the material trapped in the ice, scientists think that the pocket encases the remains of an arm of the ocean that extended into the area during the Pilocene, which ended over 1.8 million years ago. Once encased under the glacier, that pocket became hyper-saline and completely devoid of free oxygen. Consistent with its total isolation from the surface, the amount of 14C in the sample is extremely low.
The DNA sequences obtained from Blood Falls appear to come from relatives of marine organisms. Most of the clones come from within the Proteobacteria, and the closest cultured relatives of many of these metabolize sulfur and iron (there are also high levels of sulfur present in the brine).
Unlike the sulfur-powered communities present at undersea vents, there’s little indication of a hydrogen sulfide metabolism present in the ice at Blood Falls. Instead, it appears that energy is obtained when sulfur is cycled through different oxidation states by reacting it with iron, producing the Fe(II) seen in the brine. The oxidized sulfur is then used to react with carbon compounds, powering the metabolism. All of that is pretty low-energy—the authors suggest that the doubling time for a bacterium in this environment would be roughly 300 days—and requires an external source of Fe(III) to power the system. The authors posit that the glacier itself might provide the source by extracting new iron as it scrapes across the underlying rocks. The Blood Falls bacteria suggest that life could have eked out a metabolism under these extreme conditions, providing raw material for evolution once the planet warmed again.
