In Sediments Below Antarctic Ice, Scientists Discover a Giant Groundwater System
Previously Unmapped Reservoirs Could Speed Glaciers, Release Carbon
BY KEVIN KRAJICK |MAY 5, 2022
Many scientists say that liquid water is a key to understanding the behavior of the frozen form found in glaciers. Melt water is known to lubricate their gravelly bases and hasten their march toward the sea. In recent years, researchers in Antarctica have discovered hundreds of interconnected liquid lakes and rivers cradled within the ice itself. And, they have imaged thick basins of sediments under the ice, potentially containing the biggest water reservoirs of all. But so far, no one has confirmed the presence of large amounts of liquid water in below-ice sediments, nor studied how it might interact with the ice.
Now, a team from six research institutions has for the first time mapped a huge, actively circulating groundwater system in deep sediments in West Antarctica. They say such systems, probably common in Antarctica, may have as-yet unknown implications for how the frozen continent reacts to, or possibly even contributes to, climate change. The research appears today in the journal Science.
“People have hypothesized that there could be deep groundwater in these sediments, but up to now, no one has done any detailed imaging,” said the study’s lead author, Chloe Gustafson, who did the research as a graduate student at 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—whose porous qualities offer the potential to store groundwater—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.
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 U.S. Air Force LC-130 ski plane dropped Gustafson, along with Lamont-Doherty geophysicst Kerry Key, Colorado School of Mines geophysicist Matthew Siegfried, and mountaineer Meghan Seifert on the Whillans. Their mission: to better map the sediments and their properties using geophysical instruments placed directly on the surface. Far from any help if something went wrong, it would take them six exhausting weeks of travel, digging in the snow, planting instruments, and countless other chores.
The team used a tech