Why does a glacier in Antarctica run red?

From a buried sea, with a microbial community still in it. Of the clones and isolates from Blood Falls, 74 percent share high sequence homology with phylotypes from marine systems, which supports the marine origin. The library is dominated by a relative of a cold-loving marine sulfur oxidizer.

Blood Falls is the surface manifestation of brine released from below the Taylor Glacier in the McMurdo Dry Valleys of Antarctica. Geochemical analyses show that this brine is of marine origin, which already makes it a relic rather than meltwater.

The biology supports that reading. Of the clones and isolates recovered, 74 percent share high 16S rRNA gene sequence homology with phylotypes from marine systems. Two independent lines of evidence agreeing is what settles an origin question.

One organism dominates. A single phylotype made up 46 percent of the clone library and had 99 percent sequence identity with Thiomicrospira arctica, a psychrophilic marine autotrophic sulfur oxidizer. That means a cold-adapted microbe that builds itself from sulfur chemistry.

The rest is a mixed community: phylotypes related to the Betaproteobacteria, Deltaproteobacteria and Gammaproteobacteria and to the Bacteroidetes. A clone library tells you who is present, and what they are doing under the ice is a further question.