Deep beneath the ice of Antarctica, a crimson waterfall cascades into a frozen lake, its striking red color puzzling scientists for decades. Now, researchers have uncovered a surprising secret about this mysterious flow: the water contains microorganisms that trace back to the ocean—despite being buried under a massive glacier miles from the sea.
Blood Falls sits at the edge of Taylor Glacier in the McMurdo Dry Valleys region of Antarctica, pouring its rust-colored water into Lake Bonney below. The waterfall's dramatic red tint comes from iron in the salty brine beneath the glacier. But where did this hidden water come from in the first place?
Scientists led by Angela Zoumplis set out to answer that question by studying the tiny organisms living in the water, mud, and ice around Blood Falls. The team collected 167 samples from water, sediment, and air across the McMurdo Dry Valleys and used genetic techniques to identify what kinds of microbes were present.
What they found was striking. The microorganisms at Blood Falls were almost entirely species that normally live in marine environments, while surrounding areas were dominated by freshwater and land-based organisms. The researchers measured that 9.34 percent of the eukaryotes (complex organisms like algae) at the glacier terminus matched nearby ocean samples. At other Dry Valleys sites farther from the glacier, that number dropped to just 1.15 percent.
This marine signal strongly suggests that the hidden brine beneath Taylor Glacier originated as seawater. Scientists believe that long ago, when temperatures were warmer and sea levels were higher, the ocean flooded the Taylor Valley. Later, as climates cooled and sea levels dropped, the advancing Taylor Glacier trapped that ancient seawater underneath it. The marine microbes inside have likely survived there for thousands of years, isolated from the outside world.
The researchers noted that wind alone probably could not have carried these marine organisms to the glacier terminus—the genetic match is simply too strong.
The findings, published in the journal Nature Geoscience, offer new clues about how life can persist through major environmental changes. Understanding exactly when the subglacial water became trapped could also help scientists piece together the history of Antarctica's polar landscape.