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Scientists have uncovered the gruesome secret behind Antarctica's infamous Blood Falls – it's alive with the descendants of ancient sea creatures.
The eerie crimson waterfall, which pours from the Taylor Glacier into Lake Bonney, has long fascinated researchers with its blood–like appearance.
Now, a study suggests the iron–rich brine emerging from beneath the ice is home to a unique community of marine microorganisms that have been trapped beneath the glacier for hundreds of thousands of years.
These included marine diatoms, haptophytes, dinoflagellates and ciliates – tiny organisms that usually inhabit the ocean.
These are the descendants of ancient marine communities that became isolated when the glacier advanced and cut off the trapped seawater from the ocean.
The discovery provides the strongest biological evidence yet that the mysterious water originally came from the sea before being sealed beneath advancing ice.
Writing in the journal Nature Geoscience, the researchers described the site as 'a rare marine refuge in the polar desert'.
They added: 'These findings indicate that the subglacial brine–fed system at the Taylor Glacier Terminus retains marine–derived biological signatures long after physical separation from the ocean.'
The eerie crimson waterfall, which pours from the Taylor Glacier into Lake Bonney, has long fascinated researchers with its blood–like appearance
A new study suggests the iron–rich brine emerging from beneath the ice is home to a unique community of marine microorganisms that have been trapped beneath the glacier for hundreds of thousands of years. Pictured: The study area
Blood Falls gets its terrifying colour from iron–rich salty water that rusts when it reaches the air, creating its distinctive blood–red stain across the glacier.
Scientists have long suspected the brine was once seawater that flooded Taylor Valley during a warmer period before sea levels dropped and the glacier advanced over it.
Until now, however, there has been little biological proof that the trapped water really had a marine origin.
Researchers analysed 167 samples of water, sediment, ice and air collected from the McMurdo Dry Valleys and surrounding areas of Antarctica.
Using DNA sequencing, they identified thousands of different microorganisms living in and around Blood Falls.
The team discovered that the red ice, mud and sediments where the waterfall emerges were packed with species normally found in marine environments rather than on land or in freshwater.
Overall, 9.34 per cent of the microorganisms at Blood Falls were shared with nearby ocean samples, compared with just 1.15 per cent at other Antarctic Dry Valley sites.
The researchers say this strong marine fingerprint would be difficult to explain by wind blowing microbes inland from the coast.
The team discovered that the red ice, mud and sediments where the waterfall emerges were packed with species normally found in marine environments rather than on land or in freshwater
The microbes included diatoms – glass–shelled algae that form the foundation of marine food webs (left). There were also dinoflagellates, microscopic plankton that propel themselves through the water using whip–like tails (right)
The study also found many of the microorganisms are still biologically active despite surviving in one of Earth's most hostile environments.
Genetic evidence showed they were carrying out photosynthesis, repairing damaged cells and activating stress–response systems to cope with the freezing, salty conditions beneath the ice.
Some species may survive by entering dormant states, effectively lying in wait until conditions become favourable again.
The microbes included diatoms – glass–shelled algae that form the foundation of marine food webs – and haptophytes, which are tiny single–celled algae that are an important part of the ocean's plankton.
There were also dinoflagellates, microscopic plankton that propel themselves through the water using whip–like tails, and ciliates – single–celled organisms covered in hundreds of tiny hair–like structures called cilia.
Researchers say these hidden ecosystems could reveal how life survives through dramatic climate shifts over hundreds of thousands of years.
The findings may also help scientists reconstruct Antarctica's ancient history by revealing when seawater became trapped beneath the growing ice sheet.
Since Blood Falls preserves biological traces of an ancient marine world hidden beneath the frozen continent, the team says it offers a rare glimpse into ecosystems that have remained isolated ever since Antarctica's landscape was transformed by advancing glaciers.
The red waterfall stands about five storeys high in the McMurdo Dry Valleys region of Antarctica, which is known as being one of the coldest and least habitable places in the world.
It was first discovered in 1911 by the Australian geologist Griffith Taylor, who first explored the valley.
Blood Falls is the coldest known glacier–fed feature with persistently flowing water, which emerges at a temperature of about –7°C (19°F).
The lake under the glacier has an unusually salty consistency, and because saltwater has a lower freezing point than pure water and releases heat as it freezes, it melts the ice, enabling the rivers to flow.