Antarctica’s Blood Falls Teems With Mysterious Microbial Life

About 20 miles inland from Antarctica’s frigid coast, surrounded by the continent’s dry polar desert, blood red water gushes out of the stark white walls of Taylor Glacier. This iron-rich water, which gives the liquid its crimson hue, forms a mesmerizing geological feature: Blood Falls.

Blood Falls is unique in that it contains a mix of salty seawater that occasionally has fresh meltwater flowing through it. “It is extremely osmotically challenging,” said Angela Zoumplis, who is currently a postdoctoral researcher at Yale University. “You wouldn't expect anything much in that really harsh environment.”

But recently, Zoumplis, who was a PhD student at the University of California, San Diego at the time, and her colleagues made a surprising discovery. Not only did the team find a diverse population of eukaryotic microbes living in the red ice and mud around Blood Falls, but they also saw that these were marine microbes.¹ The findings, which the team published in Nature Geoscience, can help shed light on microbial adaptations to extreme environments as well as provide new insights into past and present climate change in Antarctica.

“It's this crazy interesting fascinating place on Earth,” said Andrew Alverson, a diatom researcher at the University of Arkansas who was not involved in the study. “You can learn a lot about evolution, just about how life finds a way…They came at it in a way that no one's really done before with all this DNA sequencing.”

The Hunt for Eukaryotic Microbes Across Antarctica’s Dry Valleys and Blood Falls

When Zoumplis and her colleagues arrived in the McMurdo Dry Valleys one November, it was summer in Antarctica. Their goal was to collect water, wind, and soil samples from around the valley to identify the eukaryotic microbes living there.

“[For] six to eight months, all these organisms have no water, and they're very dehydrated,” Zoumplis explained. “But for about six weeks out of the year, you have meltwater streams that flow from these glaciers, and they rehydrate these stream beds.”

To collect samples, the researchers hiked through the polar valleys—and occasionally rode a helicopter to reach remote sites. While their fieldwork took place during the summer, the expedition was far from luxurious.

“It was four months of spending pretty much the whole time in a tent in the middle of a freezing desert,” Zoumplis said. “I study cold things that live in the cold and kind of thrive in the cold, but I'm not one of those things,” she laughed, adding that, even so, she would still do it all again. “It's absolutely gorgeous out there. It's a whole lot of fun, but it is hard.”

It was during one of their sampling excursions that Zoumplis realized they were very close to Blood Falls. As a sampling location, “Blood Falls wasn't originally on our radar,” she said. “We happened to have permits, so I ran over there and just grabbed some samples, kind of not expecting anything new.”

The team collected samples of anything red that they saw: mud, ice, and sediment. Those samples “ended up turning up really really interesting for us and really surprising when we got the data back,” Zoumplis said. “Always grab everything you can get if you have the permits.”

Marine Diatoms Find a Home at Blood Falls

In total, the team collected 167 different samples: 18 at Blood Falls, 14 wind and 109 stream samples from around the McMurdo Dry Valleys, and 26 ocean water samples from the McMurdo Sound.

To ensure that they were analyzing active and living organisms, the researchers isolated RNA rather than DNA from the samples. Because DNA is more stable and long-lived compared to RNA, Zoumplis and her team reasoned that DNA might stick around even after a microbe died. “We trust RNA at the moment as more of a sign of life versus DNA,” she explained.

To identify the eukaryotic microbes, they extracted the total RNA from the samples and then amplified the 18S rRNA gene. To their surprise, they saw that the microbes in the red mud and sediment around Blood Falls were almost all marine microbes.

“And it wasn't just one taxa, but this…little group of marine eukaryotes,” she said. “Diatoms, dinoflagellates, ciliates, and they came back to be this, what we'll call a link, to the closest marine environment, which is the McMurdo Sound, Ross Sea area.” When they looked at the dry valley samples, they only found freshwater and terrestrial eukaryotes.

How had these marine microbes somehow ended up 20 miles away from the nearest sea? Prior research had identified marine bacteria in the water beneath Taylor Glacier that feeds Blood Falls, and there is geochemical evidence that the water is cryopreserved seawater.^2,3

“The idea is that potentially a flood had brought these things in,” said Zoumplis. As the climate cooled and glaciers formed, the marine microbial population could have gotten trapped at Blood Falls.

Another explanation is that the wind could have blown them in from the sea. “The dry valleys have some of the strongest winds in the world,” said Zoumplis. However, in a separate study led by her coauthor Nicholas Schulte, then a diatom researcher at the University of Colorado Boulder, the team found that modern wind currents in Antarctica’s dry valleys are highly localized, meaning that at least in modern times, marine microbes likely were not carried inland by the wind.⁴ Supporting this, they did not find any marine microbes in their wind-collected samples.

However, Zoumplis added, “We can't discount [that] historical wind blew these things in and they're just really happy to be in the salt of that brine that's outflowing [from Blood Falls].”

How To Survive As a Marine Microbe Away From the Sea

To get a better sense of what the marine microbes around Blood Falls were doing there, the team performed metatranscriptomics on their samples. They found that the microbes in the Blood Falls samples were functionally distinct from those in the aquatic samples taken from the dry valleys and from the marine microbes in the McMurdo Sound. The organisms associated with Blood Falls showed evidence of active photosynthesis and other metabolic pathways as well as elevated levels of genes involved in ion transport and sulfur assimilation. Many groups of microbes they identified also showed the potential to tolerate salinity changes in the environment, which would be advantageous at Blood Falls.

In future studies, Zoumplis would like to better understand what adaptations these microbes undergo to survive in this stressful environment. “Separating from the ocean is a really hard thing for marine life, so we think dormancy also plays a big role in this,” she said. In fact, many of the microbial taxa the team found near Blood Falls have cyst or spore lifecycle stages that allow them to persist in unfavorable environments.

Alverson is also interested in learning more about how these microbes adapted from the ocean environment to that of Blood Falls. “They must be physiologically remodeled now that they've escaped any limitation of iron or silica and they're in these sort of luxury conditions for those nutrients,” he said. “It would be amazing to grow them in the lab, stress them out,” and see what happens. He added that researchers could do pairwise experiments that compare these Blood Falls microbes to their closest marine relatives in different stressful environments.

While it would require additional sampling, both Zoumplis and Alverson would also like to see a future analysis of the genomic sequences of these microbes, which would enable phylogenetics and molecular clock analysis. With that information, “We can get an estimate on when these ocean taxa diverged from the Blood Falls taxa and then date that divergence to some event,” Zoumplis said. That could also help geologists date when a marine flood could have occurred that potentially fed Blood Falls and provide new insight into sea level rise.

Places like Blood Falls are perfect to answer these kinds of climate and evolutionary questions, Alverson said. “This is similar to the sea vents at the bottom of the ocean. You can learn a lot from these places, and they are so worth studying.”

Zoumplis concurred. “I remember doing a report in high school on Blood Falls…I never thought I'd actually get to work there,” she said. “It was an absolute dream.”