Scientists have discovered a huge underground water system in the sediments under the ice of Antarctica.

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

Previously unmapped reservoirs could accelerate glaciers and release carbon.

Many researchers believe that liquid water is essential to understanding the behavior of the frozen form found in glaciers. Melting waters have been known to soften their stony soils and hasten their march to the sea. In recent years, Antarctic scientists have discovered that hundreds of interconnected liquid lakes and rivers have been threatened in ice. They photographed thick basins of sediment beneath the ice that hold perhaps the greatest water reserves of all time. But so far, no one has confirmed the presence of significant amounts of liquid water in the sediments beneath the ice, and studied how it interacts with the ice.

Today, a research team has for the first time mapped a large amount of groundwater actively circulating in the deep sediments of West Antarctica. They say such systems, likely common in Antarctica, could have as yet unknown effects on how the frozen continent responds to or contributes to climate change. Publish the research in the journal Science May 5, 2022.

Whillans Ice Stream Study Sites

Study sites at Whillans Ice Stream. Electromagnetic imaging stations have been installed in two common areas (yellow markings). The team traveled to larger areas to perform other tasks indicated by the red dots. Click on the image to enlarge. Credit: Courtesy of Chloe Gustafson

Chloe Gustafson, lead author of the study, who conducted the research as a graduate student.[{” 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 jet ski hit Gustafson with geophysicist Kerry Key de Lamont Doherty, Colorado School of Mines geophysicist Matthew Siegfried, and mountaineer Megan Seifert in Whillans. Their mission: better map sediments and their characteristics using geophysical instruments placed directly on the surface. Beyond any help with any problems, it would take six grueling weeks of travel, snow removal, sewing machines and countless other tasks.

The team used a technology called magnetic imaging that measures the penetration to Earth of natural electromagnetic energy produced in the planet’s atmosphere. Ice, sediment, fresh water, salt water, and bedrock transmit electromagnetic energy to varying degrees; By measuring the differences, researchers can create MRI-like maps of different elements. The team placed their tools in snow pits for about a day at a time, then dug and transported them, and finally took measurements in about 40 locations. They also reanalyzed natural seismic waves emitted by Earth, collected by another team to help characterize the underlying rock, sediments and ice.

Their analysis showed that depending on the location, the sediment extended from half a kilometer to about two kilometers below the ice floor before colliding with the thing. They confirmed that the sediments were filled with liquid water along the way. Researchers estimate that if completely removed, it would form a water column 220 to 820 meters high – at least 10 times shallower than shallow hydrological systems in and on the ice floor – and possibly Much more. .

Salt water conducts energy better than fresh water, so they were able to show that groundwater becomes saltier with depth. That makes sense, Key said, because sediments are thought to have formed in a marine environment a long time ago. Ocean waters may have last reached the area covered by the Whillans during a warm period, around 5,000 to 7,000 years ago, and saturated the sediments with salt water. As the ice advanced again, it was clear that the melted fresh water was being pushed to the upper sediments by pressure from above and friction on the ice floor. Key said he can continue filtering and mixing today.

This slow drainage of fresh water into the sediments, the researchers say, could prevent water from accumulating at the base of the ice. This can act as a brake on the forward movement of the ice. Measurements by other scientists of the stable line of ice flow – the point where the current of land ice meets the floating pack ice – show that the water here is slightly less salty than normal seawater. This indicates that fresh water is draining from sediments into the ocean, allowing more meltwater to enter and keep the system stable.

But the researchers say if the surface of the ice were very thin – a distinct possibility as the climate warms – the direction of water flow could be reversed. Suspended pressures will decrease and deeper groundwater may begin to flow towards the ice base. This can increase the lubrication of the ice base and increase its forward movement. (The Whillans are already moving about 1 meter per day out to sea – too fast for glaciers.) Also, if deep groundwater flows upward, it can remove geothermal heat naturally produced in the shale. . This can melt the ice base and cause it to move forward. But it is not known if this will happen and to what extent.

“Ultimately, we don’t have any significant limitations on sediment permeability or how fast water can flow,” Gustafson said. Mentioned. Does it make a big difference that will make a quick response? Or does groundwater have a minor role in the grand ice flow pattern? “

The known presence of microbes in the shallow sediment adds another wrinkle, the researchers say. It is possible that this basin and others were inhabited below; And if the water table starts to rise, it will push out the dissolved carbon that these organisms use. Lateral groundwater flow will then send some of this carbon into the ocean. This would turn Antarctica into a hitherto unconsidered source of carbon in a world in which it is already floating. But the question is whether it will have a meaningful impact, Gustafson said.

The researchers say the new study is just the beginning of answering those questions. They wrote: “Confirming the existence of deep groundwater dynamics has changed our understanding of ice stream behavior and will require us to modify subglacial water models.”

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

Reference: 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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