Many scientists believe that understanding the behavior of glaciers’ frozen form requires the use of liquid water. Melt water is thought to lubricate their gravelly bases and speed up their journey to the sea.

In the last few years, researchers in Antarctica have found hundreds of lakes and rivers that are all connected inside the ice itself. They’ve also discovered thick sediment basins beneath the ice, which could hold the world’s largest water reservoirs.

However, no one has yet proved the presence of huge amounts of liquid water in below-ice sediments, let alone researched how it interacts with the ice.

A team has now documented a massive, actively circulating groundwater system in deep strata in West Antarctica for the first time. They claim that such systems, which are most likely found in Antarctica, may have yet-to-be-discovered consequences for how the frozen continent responds to or even contributes to climate change.

The findings were published in the journal Science today.

“People have hypothesized that there could be deep groundwater in these sediments, but up to now, no one has done any detailed imaging,” says the study’s lead author, Chloe Gustafson. “The amount of groundwater we found was so significant, it likely influences ice-stream processes. Now we have to find out more and figure out how to incorporate that into models.”

For decades, scientists have used radars and other tools to image underlying features beneath the Antarctic ice sheet. These missions have shown sedimentary basins sandwiched between ice and bedrock, among other things. However, airborne geophysics can only disclose the basic outlines of such objects, not their water content or other properties. One research in Antarctica’s McMurdo Dry Valleys in 2019 employed helicopter-borne equipment to document a few hundred meters of subglacial groundwater beneath 350 meters of ice. However, the majority of Antarctica’s known sedimentary basins are significantly deeper, and the majority of its ice is much thicker, making flying equipment ineffective. Researchers have drilled through the ice into the sediments in a few places, but only penetrated the first few meters. As a result, ice-sheet behavior models only include hydrologic systems within or slightly beneath the ice.

Most of Antarctica’s huge sedimentary basins sit below present sea level, locked between bedrock-bound land ice and floating marine ice shelves that surround the continent, which is a major flaw. They are considered to have formed on seabeds during periods of high sea levels. Ocean waters might re-invade the sediments if the ice shelves retreat in a warming climate, and the glaciers behind them could push ahead, raising global sea levels.

The latest study focused on the 60-mile-wide Whillans Ice Stream, one of a half-dozen fast-moving streams that feed the world’s largest ice shelf, which is about the size of Canada’s Yukon Territory. A subglacial lake and a sedimentary basin have been discovered beneath the ice, according to a previous study. Liquid water and a healthy community of bacteria have been discovered after shallow drilling through the first foot or so of sediments. But what lies below has remained a mystery.

Gustafson, together with Lamont-Doherty geophysicist Kerry Key, Colorado School of Mines geophysicist Matthew Siegfried, and mountaineer Meghan Seifert, were dropped on the Whillans by a US Air Force LC-130 ski jet in late 2018. Their goal was to use geophysical instruments put immediately on the surface to better map the sediments and their properties. It would take them six hard weeks of travel, digging in the snow, planting instruments, and countless other tasks if something went wrong. they couldn’t get any aid.

The researchers utilized a technique known as magnetotelluric imaging, which analyzes the amount of natural electromagnetic energy that penetrates the earth’s atmosphere. Researchers may generate MRI-like maps of the different elements by measuring the changes in how ice, sediments, fresh water, salty water, and bedrock conduct electromagnetic radiation. The crew placed their equipment in snow trenches for a day or two at a period, then dug them out and repositioned them, finally obtaining readings at more than four dozen different locations. They also reanalyzed natural seismic waves recorded by another team to assist differentiate bedrock, mud, and ice.

According to their findings, the sediments stretch from a half kilometer to nearly two kilometers below the ice’s base before striking bedrock, depending on location. They also confirmed that the sediments are saturated with liquid water throughout. According to the researchers, if all of it was recovered, it would produce a water column ranging from 220 to 820 meters high, at least 10 times higher than the shallow hydrologic systems within and at the foot of the ice, and maybe much higher.

They were also able to illustrate that the groundwater grows more saline with depth because salty water transfers energy better than pure water. This makes sense, according to Key, because the sediments are thought to have originated in a maritime environment many years ago. During a warm era 5,000 to 7,000 years ago, ocean waters most likely reached what is now the Whillans’ territory, soaking the sediments with salt water. When the ice retreated, fresh melt water was apparently driven into the higher strata by pressure from above and friction at the ice base. Key believes it is still filtering down and mixing in today.

According to the experts, the delayed drainage of new water into the sediments could prevent water from accumulating at the ice’s base. This may act as a brake on the ice’s progress. Other scientists have found that the water at the ice stream’s grounding line — where the landbound ice stream joins the floating ice shelf — is slightly less salty than regular saltwater. This indicates that fresh water is flowing through the sediments to the ocean, allowing more melt water to enter while maintaining the system’s stability.

However, if the ice surface thins, which is a probable possibility as the temperature warms, the direction of water flow could be reversed, according to the researchers. Overlying pressures would drop, allowing deeper groundwater to rise up toward the ice base. This could help to lubricate the ice’s foundation and accelerate its forward mobility. (The Whillans are already moving ice seaward at a rate of roughly a meter per day, which is quite fast for glacial ice.) Furthermore, if deep groundwater flows upward, geothermal heat naturally created in the bedrock could be carried up, thawing the ice’s base and propelling it ahead. But it’s unclear whether or not this will happen, and if so, to what extent.

“Ultimately, we don’t have great constraints on the permeability of the sediments or how fast the water would flow,” add the authors. “Would it make a big difference that would generate a runaway reaction? Or is groundwater a more minor player in the grand scheme of ice flow?”

The presence of bacteria in the shallow sediments, according to the researchers, adds another wrinkle. This basin, like others, is likely occupied deeper down, and as groundwater begins to rise, the dissolved carbon required by these species will rise with it. Some of this carbon would subsequently be carried to the ocean by lateral groundwater movement. This might convert Antarctica into a hitherto unknown supply of carbon in a world currently awash in it. But, as Gustafon pointed out, the question is whether this would have a big impact.

According to the experts, the new study is only the beginning of tackling these issues.

“The confirmation of the existence of deep groundwater dynamics has transformed our understanding of ice-stream behavior, and will force modification of subglacial water models,” they say.

Image Credit: Getty

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