An immense groundwater reservoir that sits beneath the Antarctic Ice Sheet has been mapped for the first time. The reservoir is said to extend downward for over a kilometer and could have a significant influence on how the Antarctic Ice Sheet responds to climate change and affects sea level.

The discovery marks the first evidence of the reservoir, which scientists had suspected sat beneath the ice shelf but (until now) had been unable to verify. The findings are reported in the journal Science.

The geophysical survey is the first of its kind to use magnetotelluric (MT) imaging to find and map subglacial groundwater water beneath an ice stream. These ice streams, sometimes called subglacial hydrologic systems, are plumbing networks that sit beneath glaciers.

“Ice streams are important because they funnel about 90 percent of Antarctica’s ice from the interior out to the margins,” said Chloe Gustafson, a postdoctoral researcher at UC San Diego’s Scripps Institution of Oceanography, in a statement.

They effectively lubricate where the ice shelf and the bedrock meet, meaning they can have a big influence on the movement of ice and sediment deformation beneath glaciers. These are two important processes that can shape the way frozen landscapes contribute to rising sea levels.

Until now, it was expected that these ice streams were shallow systems – but all that has been blown out of the water (so to speak) by the discovery of an immense groundwater reservoir stretching deep into the sediments that sit beneath the Antarctic Ice Shelf. As to its vastness, we’ll defer to Gustafson for a relatable comparison.

“The Empire State Building up to the antenna is about 420 meters [1,378 feet] tall. At the shallow end, our water would go up the Empire State Building about halfway. At the deepest end, it’s almost two Empire State Buildings stacked on top of each other.”

Wowzer. By comparison, Gustafson says, subglacial lakes in the area represent a comparatively puny one to four stories of the Empire State Building.

The study captured the first-ever observations of a sub-ice groundwater system of this kind thanks to MT imaging, and these showed it contains a mixture of fossil seawater and freshwater from the glacier. In case this is the first time you’re hearing that water can be a fossil, the term is used to described uncontaminated pockets of ancient water, sometimes called palaeowater.

Combined, they amount to around 10 times the volume of water found in the shallow, subglacial ice streams that sit above it. It also exchanges with the Antarctic Ice Sheet’s lubricant, meaning it also probably has implications for the ice sheet’s movements and contributions to sea levels which historically haven’t been taken into account.

As such, the authors hope future models to understand the processes will take the groundwater reservoir into account and consider that similar systems may exist elsewhere.

“We expect that similar groundwater systems exist within other marine sedimentary basins that underlie Antarctic ice stream,” they said. “Understanding the influence of this groundwater on ice sheet behavior will require its integration into the next generation of ice sheet models.”