Blood Falls Explained

Of the many extraordinary landscapes found in Antarctica, one of the most exotic is perhaps Blood Falls, where a red, briny fluid intermittently flows from the Taylor Glacier, staining the ice a dark crimson. New research reveals that ancient bacteria living in the deep, subglacial pool that serves as Blood Falls' source do some quirky chemistry (Science 2009, 324, 397).

The team of researchers led by Jill Mikucki, a microbiologist at Dartmouth College, reports that bacteria trapped 1.5 million years ago in a dark, anoxic pond 400 meters below the glacier use the abundant sulfate present as an energy source. But instead of reducing sulfate to sulfide, which is typical for bacteria in anoxic environments, the microbes use Fe³⁺ as the terminal electron acceptor, Mikucki says. When the brine from this subglacial pond rises to the surface of the glacier—for still-unknown reasons—iron from the flow precipitates as iron(III) oxide, staining the glacier red.

"We know so little about how physically isolated ecosystems function, and this one beneath the Taylor Glacier is a beautiful" example to study, comments Jan P. Amend, a geochemist at Washington University in St. Louis. Investigating low-carbon and low-oxygen systems such as this one provides insight about deep subsurface biospheres on Earth, helps narrow down origin-of-life scenarios, and aids the evaluation of whether other planets might support life, Amend adds.