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Chloe Gustafson and Meghan Seifert Install Geophysical Instruments

Scientists have discovered a massive groundwater system in sediments under Antarctic ice

Lead author Chloe Gustafson and mountaineer Megan Seifert have installed geophysical instruments to measure groundwater below the Whillans Ice Stream in West Antarctica. Credit: Keri Kee/Lamont-Doherty Earth Observatory

Previously never mapped reservoirs could accelerate glaciers and release carbon.

Many researchers believe that liquid water is key to understanding the behavior of the frozen form found in glaciers. It is known that melt water softens its gravel bases and speeds up its march towards the sea. In recent years, scientists in Antarctica discovered hundreds of interconnected Liquid lakes and rivers Threatened within the ice itself. They photographed thick basins of sediment under the ice, which likely contain the largest reservoirs of water ever. But until now, no one has confirmed the presence of significant amounts of liquid water in the sediments under the ice, nor has it investigated how it interacts with the ice.

Now, a research team has for the first time mapped a huge system of actively circulating groundwater in the deep sediments of West Antarctica. They say such systems, possibly common in Antarctica, may have as yet unknown effects on how the frozen continent reacts to, or may contribute to, climate change. Publish the research in the journal Science On May 5, 2022.

Survey Sites on Whillans Ice Stream

Survey sites on Whillans Ice Stream. Electromagnetic imaging stations were set up in two public areas (yellow marks). The team traveled to wider areas to perform other tasks, indicated by the red dots. Click on the image to see a larger version. Credit: Courtesy Chloe Gustafson

The study’s lead author, Chloe Gustafson, who conducted the research as a graduate student at[{” attribute=””>Columbia University’s Lamont-Doherty Earth Observatory. “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.”

Scientists have for decades flown radars and other instruments over the Antarctic ice sheet to image subsurface features. Among many other things, these missions have revealed sedimentary basins sandwiched between ice and bedrock. But airborne geophysics can generally reveal only the rough outlines of such features, not water content or other characteristics. In one exception, a 2019 study of Antarctica’s McMurdo Dry Valleys used helicopter-borne instruments to document a few hundred meters of subglacial groundwater below about 350 meters of ice. But most of Antarctica’s known sedimentary basins are much deeper, and most of its ice is much thicker, beyond the reach of airborne instruments. In a few places, researchers have drilled through the ice into sediments, but have penetrated only the first few meters. Thus, models of ice-sheet behavior include only hydrologic systems within or just below the ice.

Matthew Siegfried Pulls Buried Electrode Wire

Coauthor Matthew Siegfried pulls up a buried electrode wire. Credit: Kerry Key/Lamont-Doherty Earth Observatory

This is a big deficiency; most of Antarctica’s expansive sedimentary basins lie below current sea level, wedged between bedrock-bound land ice and floating marine ice shelves that fringe the continent. They are thought to have formed on sea bottoms during warm periods when sea levels were higher. If the ice shelves were to pull back in a warming climate, ocean waters could re-invade the sediments, and the glaciers behind them could rush forward and raise sea levels worldwide.

The researchers in the new study concentrated on the 60-mile-wide Whillans Ice Stream, one of a half-dozen fast-moving streams feeding the Ross Ice Shelf, the world’s largest, at about the size of Canada’s Yukon Territory. Prior research has revealed a subglacial lake within the ice, and a sedimentary basin stretching beneath it. Shallow drilling into the first foot or so of sediments has brought up liquid water and a thriving community of microbes. But what lies further down has been a mystery.

In late 2018, a USAF LC-130 ski jet shot down Gustafson, along with Lamont Doherty geophysicist Kerry Key, Colorado School of Mines geophysicist Matthew Siegfried, and mountaineer Megan Seifert on Whillans. Their mission: to better map the sediments and their properties using geophysical tools placed directly on the surface. Far from any help if something went wrong, it would take six grueling weeks of traveling, digging in the snow, planting machinery, and countless other chores.

The team used a technology called magnetic imaging, which measures the penetration of natural electromagnetic energy generated in the planet’s atmosphere into the Earth. Ice, sediment, fresh water, salt water, and bedrock conduct electromagnetic energy to various degrees; By measuring the differences, researchers can create MRI-like maps of different items. The team planted their tools in snow pits for a day or so at a time, then dug them up and moved them, eventually taking readings at about forty locations. They also reanalyzed natural seismic waves emanating from the Earth that were collected by another team to help characterize the underlying rock, sediment and ice.

Their analysis showed that, depending on the location, the sediment extends below the ice base from half a kilometer to nearly two kilometers before it hits the shale. They confirmed that the sediment was filled with liquid water along the way. The researchers estimate that, if fully extracted, it would form a water column from 220 to 820 meters in height — at least 10 times more shallow than the shallow hydrological systems within and at the ice base — and possibly much more. .

Salt water conducts energy better than fresh water, so they were also able to show that groundwater becomes saltier with depth. This makes sense, Key said, because the sediments are believed to have formed in a marine environment long ago. Ocean waters may have last reached what is now the area covered by Whillans during a warm period about 5,000 to 7,000 years ago, saturating the sediments with salt water. When the ice advanced again, it was evident that the freshwater melting from pressure from above and friction at the ice base had clearly been pushed into the upper sediments. Key said he may continue to filter and mingle today.

The researchers say this slow draining of fresh water into the sediment can prevent water from accumulating at the base of the ice. This can act as a curb on the forward movement of the ice. Measurements made by other scientists at the ice current’s land line – the point where the land ice current meets the floating ice shelf – show that the water there is somewhat less saline than normal seawater. This indicates that fresh water flows through the sediment into the ocean, making way for more meltwater to enter, and keeping the system stable.

However, the researchers say, if the surface of the ice is too thin – a distinct possibility as the climate warms – the direction of the water flow can be reversed. Suspended pressures will decrease, and deeper groundwater can begin to flow toward the ice base. This can increase the lubrication of the ice base and increase its forward movement. (Whillans is already moving toward the sea about 1 meter per day—too fast for glaciers.) Moreover, if deep groundwater is flowing upward, it can carry away geothermal heat naturally generated in shale. This may melt the ice base and push it forward. But whether and to what extent this will happen is not clear.

“Ultimately, we don’t have significant limitations on sediment permeability or how fast the water can flow,” Gustafson said. Would it make a huge difference that would generate a quick reaction? Or does groundwater play a minor role in the grand scheme of ice flow? “

The researchers say the known presence of microbes in the shallow sediments adds another wrinkle. It is probable that this basin and others were inhabited below; And if the groundwater begins to rise, it will take out the dissolved carbon that these organisms use. Lateral groundwater flow will then send some of this carbon to the ocean. This would turn Antarctica into a previously unconsidered carbon source in a world it already swims in. But the question again is whether this will make some significant impact, Gustafson said.

The researchers say the new study is just the beginning of answering these questions. They wrote: “Confirmation of the existence of deep groundwater dynamics has changed our understanding of the behavior of glacial currents, and will force us to modify subglacial water models.”

Other authors are Helen Fricker of the Scripps Institution of Oceanography, J. Paul Winberry of Central Washington University, Ryan Ventorelli of Tulane University, and Alexander Michaud of Bigelow Oceanographic Laboratory. Chloe Gustafson is now a postdoctoral researcher at Scripps.

Reference: “A dynamic system of saline groundwater mapped down an Antarctic ice stream” by Chloe D. Gustafson, Keri K, Matthew R. Siegfried, J. Paul Winberry, Helen A. Fricker, Ryan A. May 2022, Science.
DOI: 10.1126 / science.abm3301

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