(ORDO NEWS) — Beneath a fast-flowing ice stream in West Antarctica, scientists have discovered a vast aquifer filled with sea water that has likely been stored there for thousands of years.
For the first time, scientists have discovered groundwater under an ice stream in Antarctica, and the discovery could change our understanding of how the frigid continent is responding to climate change and what mysterious organisms lurk beneath its many ice shelves.
The discovered groundwater system can be thought of as a giant sponge of porous sediments and saturated with water, says Chloe D. Gustafson, lead author of the new buried aquifer study, formerly a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory and now at the Oceanographic Institute Scripps at the University of California, San Diego.
The ‘sponge’ we’re seeing is between half a kilometer and two kilometers [0.3-1.2 miles] thick, so it’s pretty deep.
Gustafson and her colleagues described the huge aquifer in a paper published Thursday (May 5) in the journal Science. The aquifer is under the same ice flow as subglacial Lake Willans, which is shallower, about 2,625 feet (800 meters) below the ice.
“For me, the most surprising result is the sheer volume of water contained in the aquifer,” said Winnie Chu, a glacier geophysicist at Georgia Institute of Technology’s School of Earth and Atmospheric Sciences, who was not involved in the study.
The authors calculated that the huge aquifer contains more than 10 times more water than the smaller system of lakes and rivers located at the base of the ice shelf. This shallow system includes Whillans Lake, which is 20 square miles (60 square kilometers) in area and about 7 feet (2.1 m) deep.
Scientists have long suspected that vast aquifers could be hiding beneath Antarctic ice, in part because the continent’s ice flows and glaciers slide over a layer of permeable sediment that water must penetrate, Chu said.
However, until now, technological limitations have prevented researchers from collecting direct evidence for the existence of such deep hydrological systems, that is, systems made up of water, she explained. Instead, research has focused on relatively shallow lakes and rivers located at or near the base of glaciers and ice shelves.
To look beyond these shallow water systems to the depths beneath them, Gustafson and her colleagues used a technique called magnetotelluric imaging. They took measurements in West Antarctica’s Willans Ice Stream, a moving belt of ice about 0.5 miles (0.8 km) thick that moves 6 feet (1.8 m) per day towards the nearby Ross Ice Shelf.
Magnetotelluric imaging is based on electromagnetic fields created by solar winds interacting with the Earth’s ionosphere – a dense layer of molecules and electrically charged particles in the upper atmosphere.
When the solar winds hit the ionosphere, they excite the particles in it and generate moving electromagnetic fields that penetrate the Earth’s surface.
These moving fields then give rise to secondary fields in ice, snow, and sediment, and it is these secondary fields that magnetotelluric instruments measure. The team buried the instruments in shallow holes in the snow and collected data from about four dozen different locations along the ice stream.
“These secondary fields are very closely related to geology and hydrology,” which means ice looks very different from sediment, salt water looks different from fresh water, and so on, Gustafson said.
“It’s like doing an MRI of the Earth, and our signal comes from the sun interacting with the Earth’s magnetic field,” she said.
Other teams of scientists have already used this mega-MRI in Antarctica to study the Earth’s crust and upper mantle; these studies began back in the 1990s, according to a 2019 review in the journal Surveys in Geophysics.
Instead, Gustafson’s team took measurements from a shallower depth, from the base of the creek to a depth of about 3 miles (5 km). There, they found a thick sedimentary sponge with incredibly salty sea water at its deepest point and fresh water at its shallowest, where the sponge meets the icy stream.
This gradient suggests that shallow subglacial systems are connected to a deep aquifer, Gustafson says, and that both are likely to influence the ice flow above.
“It’s not clear right now whether an aquifer can occasionally exchange water with subglacial hydrology or if it’s a one-way exchange” where water from a glacial stream seeps down and then remains in the aquifer for a while, Chu said.
Depending on the scenario, the aquifer may lubricate the ice flow by periodically pumping water into the subglacial system, or remove water from the system; both of these dynamics will affect the course of the ice stream above, Chu added.
The exchange of water between deep and shallow water systems can also affect which types of micro-organisms grow under the ice flow and how those micro-organisms survive, Gustafson said.
This is because the flow of liquid water through the aquifer and the interconnected lakes and rivers above stimulates the flow of nutrients in the ecosystem. In addition, the gradient from salt water to fresh water determines which types of microbes can survive in each environment.
As for the most saline water in the depths of the aquifer, the authors suggested that it probably entered the groundwater system from the ocean about 5-7 thousand years ago, during the warm period in the middle of the Holocene epoch, when the West Antarctica ice sheet retreated.
Then, “as the ice sheet receded, the presence of thick ice blocked the ocean’s access to the bottom, and the remaining seawater was sealed as groundwater under the Willans Ice Stream,” Chu wrote in a commentary on the study, also published May 5 in the journal Science.
This is the first time an aquifer has been discovered under the Whillans Ice Stream, but the research team suspects that similar hydrological systems lie beneath all ice streams in Antarctica and are just waiting to be discovered.
These groundwater systems likely “extend hundreds of kilometers deep into the ice sheet,” Gustafson said. The next step is to gather evidence for the existence of such systems elsewhere on the continent and compare what they found at Willans with other regions.
In particular, how might the aquifer under the rapidly thinning Thwaites Glacier, also known as the “Doomsday Glacier”, differ from the aquifer under Willans, and how do these deep systems affect the flow and melting of overlying ice?
Current glacial flow models do not account for such aquifers, Gustafson said, so this will be an interesting area of research in the future.
“We still have a lot to learn about the relationship between groundwater hydrology and the rest of the ice sheet’s hydrology before we can say anything concrete about how groundwater hydrology could impact the impacts of climate change in Antarctica,” Chu said.
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