Skip to Main Content
Skip Nav Destination

Groundwater flows deep under Antarctic ice

23 May 2022

Ice-dynamics models must be updated now that researchers have observed a thick layer of salty water in sediments beneath the West Antarctic Ice Sheet.

Two people in red snow jackets standing on a field of snow and ice
Matthew Siegfried (left) and Chloe Gustafson (right) use a radar instrument to measure ice thickness in West Antarctica. Credit: Kerry Key

Some 70% of Earth’s fresh water is stockpiled in Antarctica’s ice. If it were all to melt, global sea level would rise by 58 m. Estimates of ice loss critically depend on such factors as the conditions at the base of an ice sheet and the stability of ice shelves that prevent the sheet from sliding into the ocean. (For more on Antarctica’s ice shelves, see the article by Sammie Buzzard, Physics Today, January 2022, page 28.)

If enough water melts at the ice sheet’s bed, the friction between the ice and the land decreases, and the ice flows toward the ocean faster. But researchers have long hypothesized that underground water below the ice may also help to reduce sliding friction.

Despite the potential importance of groundwater to ice-sheet dynamics, the remote and harsh environment of Antarctica and the technical challenges of identifying water hundreds of meters beneath the ice surface have prevented glaciologists from drawing any conclusions about its existence. But now Chloe Gustafson of the University of California, San Diego, and her colleagues have conclusively observed groundwater under the Whillans Ice Stream—a river of ice flowing from the West Antarctic Ice Sheet on land to the Ross Ice Shelf floating off the Siple Coast. Their approach indicates that the 1-km-thick basin of groundwater contains about an order of magnitude more water than previous estimates of subglacial hydrological systems.

To image subglacial groundwater, researchers have used seismometers and ground-penetrating radar instruments. Although those methods have been able to measure ice thickness to a few hundred meters, they aren’t adept at measuring the volume of water in deeper reservoirs, in part because radar signals are easily absorbed in water.

In a 2017 modeling study, two of Gustafson’s coauthors—Kerry Key and Matthew Siegfried—found that a magnetotellurics (MT) approach should be capable of detecting groundwater below ice sheets in Antarctica. Magnetotellurics is a passive method that measures the electrical conductivity of the subsurface. Natural variations in electric and magnetic fields arise from the interaction of charged particles in the solar wind with Earth’s conductive magnetosphere. MT measurements are capable of distinguishing high-resistivity glacier ice from low-resistivity sediments whose pore space holds subglacial groundwater.

From November 2018 to January 2019, during the field season in Antarctica, Gustafson and her colleagues collected MT data on the Whillans Ice Stream. From that data and a passive seismic survey, the researchers examined a sedimentary basin underneath some 800 m of ice.

In that deep reservoir, they found a subglacial water system. To their surprise, the researchers learned that some of the groundwater was salty. The salinity increased with depth and had values approaching that of seawater. The MT measurements revealed that in the top few hundred meters of the basin below the ice sheet, fresh meltwater mixed with the saltier deep groundwater, a connection whose existence had only been suggested theoretically before this study.

The saltiness of the groundwater suggests that seawater may have infiltrated into the subglacial system 5000–7000 years ago when seawater advanced farther inland than it reaches today. Now that the groundwater has been conclusively observed, the next step will be to incorporate the results into ice-flow models to determine to what extent the ice-sheet velocity is affected by subglacial groundwater. (C. D. Gustafson et al., Science 376, 640, 2022.)

Close Modal

or Create an Account

Close Modal
Close Modal