Beneath Antarctica's ice-free McMurdo Dry Valleys lies a salty aquifer that may support previously unknown microbial ecosystems and retain evidence of ancient climate change, according to a new study published April 28 in Nature Communications.
UC Santa Cruz glaciologist Slawek Tulaczyk was part of a team of researchers who gathered compelling evidence of groundwater in the Dry Valleys using a novel, helicopter-borne sensor to penetrate below the surface of large swathes of terrain. The team found that brines (salty water) form extensive aquifers below glaciers and lakes and within permanently frozen soils. The brines may also play an important role in contemporary biological processes in the Dry Valleys.
"Our electromagnetic data indicate that the margins of Antarctica may shelter a vast microbial habitat, in which the limits of life are tested by difficult physical and chemical conditions," said Tulacyzk, a coauthor of the paper and professor of Earth and planetary sciences at UC Santa Cruz. "Over billions of years of evolution, microbes seem to have adapted to conditions in almost all surface and near-surface environments on Earth. Tiny pore spaces filled with hyper-saline brine staying liquid down to minus 15 degrees Celsius [five degrees Fahrenheit] may pose one of the greatest challenges to microbes."
Past surface ecosystems
First author Jill Mikucki of the University of Tennessee, Knoxville, led the study. "These unfrozen materials appear to be relics of past surface ecosystems, and our findings provide compelling evidence that they now provide deep subsurface habitats for microbial life despite extreme environmental conditions," Mikucki said. "We believe the application of novel below-ground visualization technologies can not only reveal hidden microbial habitats, but can also provide insight on glacial dynamics and how Antarctica responds to climate change."
The team found evidence that brines flow towards the Antarctic coast from roughly 18 kilometers (11 miles) inland, eventually discharging into the Southern Ocean. It is possible that nutrients from microbial weathering in these deep brines are released into the ocean and affect near-shore biological productivity. However, the vast majority of Antarctica's coastal margins remain unexplored. This new survey highlights the importance of these sensitive interfaces.
In addition to providing answers about the biological adaptations of previously unknown ecosystems that persist in the extreme cold and dark of the Antarctic winter, the new information could also help scientists to understand whether similar conditions might exist elsewhere in the solar system. During the Antarctic summer, conditions in the Dry Valleys resemble those on the surface on Mars.
The researchers were part of an international, interdisciplinary team that used a transient electromagnetic sensor called SkyTEM, mounted to helicopter, to produce extensive imagery of the subsurface of the Dry Valleys, the coldest, driest desert on our planet. Using a helicopter to make the observations allowed large areas of rugged terrain to be surveyed.
The new SkyTEM results shed light on the history and evolution of the Dry Valley landscape, the largest ice-free region in Antarctica. During the height of the southern summer, the Dry Valleys have free-flowing rivers and streams. They are also home to briny lakes at the surface and beneath at least one of the glaciers that intrude into the Valleys.
During the surveys, SkyTEM was flown over the Taylor Glacier, one of the best-studied glaciers in the world. Taylor Glacier has a unique feature known as Blood Falls, where red, iron-rich brine from the subsurface is released at the front of the glacier. Blood Falls is known to harbor an active microbial community where organisms use iron and sulfur compounds for energy and growth and, in the process, facilitate rock weathering.
According to Tulaczyk, the newly discovered brines beneath the Dry Valleys may harbor similar microbial communities. He is involved in another project in which researchers are drilling into Taylor Glacier to extract samples of the brine that emerges at Blood Falls.
Antarctic climate change
Research in the Dry Valleys may help scientists understand how the Antarctic climate has changed over geologic time, said coauthor Ross Virginia, a biogeochemist at Dartmouth College. "This project is studying the past and present climate to, in part, understand how climate change in the future will affect biodiversity and ecosystem processes," Virginia said. "This fantastic new view beneath the surface will help us sort out competing ideas and theories about how the Dry Valleys have changed with time and how this history influences what we see today."
The SkyTEM technology was developed at Aarhus University in Denmark. SkyTEM lead Esben Auken has flown the sensor all over the world, but this was the first time they tackled Antarctica. "Antarctica is by far the most challenging place we have been," Auken said. "It was all worth it when we saw the raw data as it was offloaded from the helicopter; it clearly showed we were on to some extraordinary results which no one had been able to produce before."
Co-authors on the paper include researchers from UC Santa Cruz, University of Tennessee, Dartmouth College, University of Illinois at Chicago, Louisiana State University, University of Wisconsin, Aarhus University in Denmark, and Sorbonne Universités, UPMC University in France.
The National Science Foundation's Division of Polar Programs supported the SkyTEM project through a collaborative award to Mikucki, Virginia, and Tulacyzk. The division manages the U.S. Antarctic Program, through which it coordinates all U.S. scientific research on Antarctica and provides the logistical support to that research.