Stanford University
Meltwater stream on glacier in Greenland

Scientists find missing piece in glacier melt predictions

A new method for observing water within ice has revealed stored meltwater that may explain the complex flow behavior of some Greenland glaciers, an important component for predicting sea-level rise in a changing climate.

BY Danielle Torrent Tucker
ClockOctober 15, 2018

Stanford scientists have revealed the presence of water stored within a glacier in Greenland, where the rapidly changing ice sheet is a major contributor to the sea-level rise North America will experience in the next 100 years. This observation – which came out of a new way of looking at existing data – has been a missing component for models aiming to predict how melting glaciers will impact the planet.

The group made the discovery looking at data intended to reveal the changing shape of Store Glacier in West Greenland. But graduate student Alexander Kendrick figured out that the same data could measure something much more difficult to observe: its capacity to store water. The resulting study, published in Geophysical Research Letters, presents evidence of glacier meltwater from the surface being stored within damaged, solid ice. While ice melting at the surface has been well documented, little is known about what happens below glacier surfaces, and this observation of liquid water stored within solid ice may explain the complex flow behavior of some Greenland glaciers.

“Things like this don’t always come along, but when they do, that is the real ‘joy of the discovery’ component of Earth science,” said co-author Dustin Schroeder, an assistant professor of geophysics at Stanford University’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “This paper not only highlights this component’s existence, but gives you a way to observe it in time.”

Surface meltwater plays an important role in Greenland by lubricating the bottoms of ice sheets and impacting how retreating glaciers are affected by the ocean. The process of how the glaciers melt and where the water flows contributes to their behavior in a changing climate, as these factors could alter glaciers’ response to melting or impact the timeline for sea-level rise. Knowing that some liquid is intercepted within glaciers after melting on the surface may help scientists more accurately predict oceanic changes and help people prepare for the future, Schroeder said.

“All of our predictions of sea-level rise are missing this meltwater component,” Schroeder said. “I think we’re only just realizing how important it is to understand at a fundamental physical scale what glacier meltwater does on its way from the surface to the bed.”

This component Alex has discovered shows that there is a piece of this glacier in particular – and maybe the entire Greenland hydrologic system in general – that we just were not modeling or thinking about in this way.

A different perspective

The researchers analyzed data from a high-resolution, low-power radio-echo sounder (ApRES) collected hourly from May to November 2014. Behaving like an ultrasound for ice, the radar sends an electronic wave that bounces off variations in ice density to create an image of ice structure that shows how quickly the ice melts or moves over time.

When the team plotted the radar data, it looked suspicious, said Kendrick, who was lead author on the paper. They tested ideas such as temperature variations and battery fluctuations to account for what they saw, then wondered if water within the ice was causing the peculiarity. By looking at a different aspect of the data, Kendrick noticed that the idiosyncrasies coming from deep within the glacier correlated with information from a nearby weather station indicating that the glacier had been melting at the time the data was collected. That finding backed up the idea that they were detecting water that had melted on the surface and then trickled down into the glacier, where it got trapped.

Radar signal in glacier over time.
Meltwater accumulation within 160 feet of the surface causes these bright, white reflections to dim to grey from June to early August before stabilizing in late August. (Image credit: Alexander Kendrick)

“This is a new way you could use these instruments to answer scientific questions – instead of just looking at changes in the ice thickness, we’re also looking at changes in the ice properties itself,” said co-author Winnie Chu, a postdoctoral researcher in Schroeder’s lab. “Alex set up the groundwork for trying to understand how this meltwater storage changes through time.”

The study reveals a significant amount of meltwater produced from the local area surrounding the radar is being intercepted and stored within the ice in a region extending between 15 to 148 feet below the surface during the summer, then released or refrozen during winter.

“The water system of Greenland is critical for understanding what’s happening on the planet,” said Schroeder, who is also a fellow at the Stanford Woods Institute for the Environment. “This component Alex has discovered shows that there is a piece of this glacier in particular – and maybe the entire Greenland hydrologic system in general – that we just were not modeling or thinking about in this way.”

The researchers hope this new geophysical method can be used to understand how meltwater impacts other glaciers and glacial systems, as well.

This research is part of a collaboration led by co-author Poul Christoffersen at the University of Cambridge. The study includes co-authors from the University of Cambridge, the British Antarctic Survey, the University of St Andrews, Aberystwyth University, the Geological Survey of Denmark and Greenland, the University of Tromsø, University College London and the British Antarctic Survey. The work was partially funded by NASA.

Alexander Kendrick.
Alexander Kendrick. (Photo credit: Meredith Goebel)

Intellectual cross-pollination

Radar data from Greenland’s Store Glacier had been tucked away in professor Dustin Schroeder’s files until graduate student Alexander Kendrick approached the radio glaciologist with a request. He wanted to use the data in a second research project, a graduation requirement for PhD students in geophysics. “Because of Alex, we could work on this more out-of-the box, high-risk creative project,” Schroeder said.

 

For Kendrick, the requirement to carry out a completely unrelated project “helped solidify that geophysics was the right field for me,” he said. “You can take a break, work on another project and reprogram your mind a little bit – it gives you a new sense of clarity.” With his PhD advisor, Rosemary Knight, Kendrick analyzes fluid flow through porous materials like sand, gravel and clay that can be used to understand groundwater on a large scale. “Our fields are in very different states, our approaches are very different, and Alex took insights from Rosemary and brought it into our field,” Schroeder said. “There really is this intellectual cross-pollination.”

Media Contacts

Alexander Kendrick

School of Earth, Energy & Environmental Sciences

(650) 725-1331, alexkend@stanford.edu

Dustin Schroeder

School of Earth, Energy & Environmental Sciences

(650) 725-7861, Dustin.M.Schroeder@stanford.edu

Winnie Chu

School of Earth, Energy & Environmental Sciences

(650) 497-6509, wchu28@stanford.edu

Danielle T. Tucker

School of Earth, Energy & Environmental Sciences

(650) 497-9541, dttucker@stanford.edu

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