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Why is this Antarctic Glacier “Bleeding?”

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A five-story wall of ice in East Antarctica has been oozing rust-red brine for more than a century, and researchers only recently nailed down exactly why.

Blood Falls sits at the snout of Taylor Glacier in the McMurdo Dry Valleys, staining the ice above Lake Bonney a deep crimson as it discharges. PBS Terra’s Antarctic Extremes series tackled the mystery in its episode “Why is this Antarctic Glacier ‘Bleeding?’,” walking through more than a century of competing theories before landing on the real culprit: rusting iron trapped in ancient, hypersaline water. The formation has become one of the more instructive case studies in extremophile science, and it doubles as a stand-in for what researchers expect to find under the ice shells of other worlds.

• Blood Falls was first documented in 1911 by Australian geologist Thomas Griffith Taylor, who assumed the red color came from algae — a theory that held for decades before being disproven.
• The discharge is a hypersaline brine sealed beneath the glacier for an estimated 1.5 to 2 million years, carrying dissolved ferrous iron that turns rust-red only after it hits atmospheric oxygen.
• Research published in the Journal of Glaciology, involving glaciologists Erin Pettit and Jessica Badgeley alongside microbiologist Jill Mikucki, explained how the brine keeps flowing beneath ice that sits well below the 32°F freezing mark.

A Mistaken Diagnosis From 1911

When Thomas Griffith Taylor first spotted the crimson streaks running down the glacier that would later bear his name, red algae seemed like the obvious explanation — it was a known culprit for tinting snow and ice elsewhere in the world. That assumption stuck for years, in part because nobody could get a clean look at what was actually seeping out of the ice or where it originated. It took modern drilling, sampling, and chemical analysis to establish that the color had nothing to do with biology at all, and everything to do with chemistry happening far below the surface.

Cracking the Chemistry of the Crimson Brine

Microbiologists and glaciologists, including Jill Mikucki, eventually traced the red stain to a reservoir of hypersaline water that has been sealed beneath Taylor Glacier for 1.5 to 2 million years. That brine is loaded with dissolved ferrous iron, and underground, cut off from air, it stays clear. The moment it escapes through crevasses at the glacier’s snout and meets oxygen, the iron oxidizes almost instantly, rusting the ice a deep red — the same basic chemistry that turns an old nail orange, just playing out on a five-story scale.

The brine has been locked under the ice for up to 2 million years — and it stays perfectly clear until the second it touches air.

Solving the Physics of Water That Shouldn’t Flow

The bigger puzzle wasn’t the color — it was how liquid water moves through a glacier frozen well below 32°F in the first place. Studies published in the Journal of Glaciology, with work from Erin Pettit and Jessica Badgeley, worked out the mechanism: the brine’s extreme salt content depresses its freezing point far below that of fresh water, and as portions of it do freeze, the latent heat released warms the surrounding ice just enough to keep a pathway open. That combination lets the ancient reservoir keep escaping through fissures instead of locking up solid, which is exactly what allows Blood Falls to keep “bleeding” year after year.

A Test Site for Life Beyond Earth

The subglacial reservoir feeding Blood Falls isn’t just salty and ancient — it’s home to an active microbial ecosystem that survives in total darkness with no oxygen, metabolizing sulfate and iron to stay alive. That makes the site one of the closest terrestrial matches to what scientists suspect could exist beneath the icy crusts of Mars, Europa, and Enceladus, where similar dark, oxygen-starved, briny environments are considered the best candidates for extraterrestrial life. Anyone curious about how extreme environments force life and geology into strange arrangements might also enjoy the volcanic oddity chronicled in Unusual ‘Lava Eggs’ Appear by Volcano, or the underground formations detailed in World-class sinkholes attract divers to South Australian farms.

That’s really the whole reason astrobiologists keep flying researchers out to a frozen valley cut off by the Transantarctic Mountains instead of just running simulations in a lab — Blood Falls is a working model of a sealed, lightless, salty ecosystem that’s already survived for up to 2 million years, and if anything like it is going to turn up under the ice on Europa, this is the closest thing on Earth to a dry run.