Water beneath glaciers may surge due to thinning ice sheets

Thinning ice sheets may be more than just markers of global warming; they may also be indicative of a significant increase in subglacial waters flowing out into the ocean. This alarming possibility is the outcome of a new study led by Georgia Tech researchers Alex Robel and Shi Joyce Sim.

In collaboration with Colin Meyer from Dartmouth, Matthew Siegfried from Colorado School of Mines, and Chloe Gustafson from the USGS, the team formulated a new model that is challenging previous assumptions. 

Profound implications 

The findings, published in the journal Science Advances, suggest that we might be grossly underestimating the amount of subglacial water draining into our oceans. 

Specifically, there could be up to twice the amount of subglacial water than initially believed. This revelation holds profound implications for glacial melt, sea level rise, and even marine biology.

While the concept of studying subglacial flow is not new, the methodology adopted by many scientists is cumbersome, entailing time-consuming computations. 

Focus of the study

The uniqueness of the study lies in its methodology. The researchers created a simple, yet effective equation which makes predictions based on satellite measurements of Antarctica and thinning ice sheets from the last twenty years.

“In mathematical parlance, you would say we have a closed form solution,” said Professor Robel. “Previously, people would run a hydromechanical model, which would have to be applied at every point under Antarctica, and then run forward over a long time period.”

Simple approach to a complex issue

The brilliance of their approach is in the simplicity. As Professor Robel points out, using their equation, the entire prediction can be performed on a basic laptop in mere seconds. 

The team tailored their theory for specific conditions that exist beneath ice sheets. As he put it, “This is, to our knowledge, the first mathematically simple theory which describes the exfiltration and infiltration underneath ice sheets.”

Echoing Professor Robel’s enthusiasm, Sim said: “It’s really nice whenever you can get a very simple model to describe a process – and then be able to predict what might happen, especially using the rich data that we have today. It’s incredible. Seeing the results was pretty surprising.”

Alarming feedback cycle 

The research sheds light on a concerning feedback cycle. Aquifers, essentially underground reservoirs, can release water when the weight on them reduces, a process known as exfiltration. 

Historically, the focus on exfiltration has been on longer time frames like interglacial cycles. Modern-day ice sheets, particularly those thinning in Antarctica, have garnered less attention.

However, with the innovative theory and recent satellite data, Robel and Sim are filling this knowledge gap. 

Concerning revelations

Professor Robel raised a concerning possibility: “There’s a wide range of possible predictions. But within that range of predictions, there is the very real possibility that groundwater may be flowing out of the aquifer at a speed that would make it a majority, or close to a majority of the water that is underneath the ice sheet.”

Another crucial element that the study illuminates is the nature of the Antarctic ice sheet itself. Contrary to popular belief, the warmest part of the ice sheet isn’t on its surface but at its very base, thanks to the geothermal heat trapped underneath. 

This understanding paints a clearer picture: thinning ice sheets allow for increased exfiltration which, in turn, accelerates the melting of the ice.

“When the atmosphere warms up, it takes tens of thousands of years for that signal to diffuse through an ice sheet of the size of the thickness of the Antarctic ice sheet. But this process of exfiltration is a response to the already-ongoing thinning of the ice sheet, and it’s an immediate response right now,” explained Professor Robel.

Study implications 

This research doesn’t just stop at glacial melt and rising sea levels. Some of the richest marine environments thrive off Antarctica’s coast. 

Understanding exfiltration better could be pivotal for marine biologists aiming to gauge marine productivity and how it will change in the future. 

Robel also hopes this work will open the doorway to more collaborations with groundwater hydrologists who may be able to apply their expertise to ice sheet dynamics, while Sim underscores the need for more fieldwork.

“Getting the experimentalists and observationalists interested in trying to help us better constrain some of the properties of these water-laden sediments – that would be very helpful,” said Sim. “That’s our largest unknown at this point, and it heavily influences the results.”

“It’s really interesting how there’s a potential to draw heat from deeper in the system. There’s quite a lot of water that could be drawing more heat out, and I think that there’s a heat budget there that could be interesting to look at.”

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