Researchers have identified a huge underground reservoir of water near the Ross Ice Shelf in Antarctica. The liquid water is in a sedimentary basin that is up to 1.3 kilometers deep. If the sediment were removed, the water column would be between 220 and 820 meters high. The explorers theorize that the water affects the speed of the overlying Whillans Ice Flow and that there are other deep water reservoirs in Antarctica. The study by the research group led by Chloe Gustafson from Columbia University in Palisades in the US state of New York is in the journal Science published.
“Others have hypothesized that there may be deep groundwater in these sediments, but no one has done detailed imaging until now,” Gustafson explained. She and her team used seismometers and the so-called passive seismic method to draw conclusions about the structure of the subsoil by analyzing light seismic waves. They also used a technology that had previously only been used in Antarctica to elucidate structures at a depth of ten or more kilometers: magnetotellurics.
The scientists evaluate data on the electrical conductivity of structures in the subsoil. Natural magnetic fields trigger electrical eddy currents in the earth’s interior, which in turn generate magnetic fields that can then be recorded and analyzed. Using this technology, Gustafson and colleagues were able to determine the depth and extent of the sedimentary basin. Since salt water conducts electricity better than fresh water, they were also able to determine the salinity of the water: it is lower in the upper part of the sediment than in sea water, but increases with depth.
Does the water slow down the glacier or does it accelerate it?
The researchers interpret this result as follows: Thousands of years ago, the sedimentary basin was a seabed, which is why the sediment is filled with salt water. For the researchers, the decreasing salt content is an indication that the water reservoir is connected to the meltwater on the glacier floor, i.e. that meltwater has seeped in. The water on the glacier floor reduces friction as the glacier moves over rock or sediment. So the water affects the flow rate of the glacier and the amount of ice that gets into the sea – and which then contributes to the rise in sea level as a result of climate change.
Chloe Gustafson and mountaineer Meghan Seifert install a magnetotelluric device on the glacier.
(Photo: Kerry Key/Lamont-Doherty Earth Observatory, Columbia University)
In order to better understand the influence of groundwater on the behavior of glaciers, such water reservoirs should be integrated into the next generation of ice sheet models, the scientists recommend. They also recommend using magnetotellurics, which is based on electromagnetics, as a measurement method: “I hope that people will consider electromagnetics as part of the standard Antarctic geophysical toolkit,” said Gustafson, who also works at the University of California San Diego in La Jolla.
In a comment in Science Points out Winnie Chu of the Georgia Institute of Technology in Atlanta that groundwater could also be helping the glacier flow more slowly: “If the groundwater reservoir can hold a significant amount of subglacial water, the amount of smear water that goes to the Sliding on solid ground contributes, reduces.” How the groundwater actually affects glacier behavior still needs to be researched.