Enlarge / Conservation efforts for the shoe included careful reshaping and freeze-drying. (credit: Secrets of the Ice )

Sometime between 200 and 500 CE, someone crossing a high mountain pass in Norway discarded a shoe. More than 1,500 years later, an unusually warm summer melted centuries of accumulated snow and ice , revealing the ancient shoe—and an assortment of other objects left behind by ancient and medieval travelers on the snowy mountain trails. Archaeologists with the Secrets of the Ice project recovered the shoe in 2019, finished conserving it in 2021, and recently published a report about the site and the finds.

The report “is for internal archiving only and [is] not published,” Secrets of the Ice co-director Lars Holger Pilø told Ars in an email. “In addition, it is in Norwegian.”

But Pilø and his colleagues recently shared some highlights via the project’s social media and in a conversation with Ars.

Enlarge / Sensors, support electronics, and a transmitter are all encased in a pressure-proof shell. (credit: Michael Prior-Jones)

Through the GRACE satellite program, researchers have shown that Greenland’s ice sheet has been losing about 280 billion tons of ice each year—the equivalent of close to 1.5 million Olympic swimming pools . For glaciers like those in Greenland and Antarctica, most of this meltwater ends up in the ocean—with already noticeable consequences for rising sea levels.

Better predictions of future sea level rise will require us to understand what meltwater is doing inside—and especially underneath—glaciers. But to do this, researchers need to take measurements through a glacier. Earlier this month, electrical engineer and glaciologist Dr. Michael Prior-Jones and his collaborators in the UK, Switzerland, Denmark, and Canada published their redesigned version of a wireless subglacial probe— the Cryoegg —to help study the inner “plumbing” of glaciers.

Glacial obstacles

The meltwater flowing through and underneath glaciers can end up in small pockets, large lakes, or fast-moving rivers—each of which destabilizes the overlying glacier to different degrees. Subglacial lakes can cause entire sections of the glacier to shift. In contrast, subglacial rivers channel meltwater into a smaller area, causing comparatively less glacial movement.

Enlarge / Clouds obscure the waters off Greenland's southwest coast. (credit: NASA EO )

While the GRACE satellites were active, their incredibly precise gravity measurements tracked a loss of about 280 billion tons of ice from Greenland each year. That's glacial land ice that raises sea level as it flows into the ocean—and it's vanishing at a remarkable clip. But just how remarkable is that clip? We don't have such excellent measurements going back too far into Greenland's history.

A new study led by the University of Buffalo's Jason Briner takes this question on. We have lots of paleoclimate records of climate conditions in Greenland, the position of the ice on the landscape, and even changes in sediments carried into the sea by meltwater. None of that directly tells you how much ice was accumulating or disappearing. To put the pieces together and calculate that, you need to combine that data with a model.

Digital ice

The researchers used a high-resolution ice-sheet model simulating (roughly) the southwest quadrant of Greenland. There's a good reason for that: the ice sheet mostly melts before reaching the ocean here, making it the simplest area to simulate. Since we've been tracking things, the year-to-year growth or losses of the ice sheet here nicely mirror the Greenland-wide total. So simulate this area well, and at high resolution, and your numbers should scale to the whole ice sheet.

Enlarge / Glacial meltwater lakes in the Bhutan Himalaya. (credit: NASA EO )

When we talk about sea level rise, one of the causes we have to mention is the shrinking of mountain glaciers, which are often overlooked as we focus on the monster ice sheets of Greenland and Antarctica. Seas rise because glacial ice melts and meltwater makes its way to the ocean, turning land ice into ocean volume. But this description is obviously a simplification. For mountain glaciers, the meltwater has to do some traveling to reach the ocean, and interesting things may happen along that journey.

That journey creates a known blind spot in the math. Sea level rise is measured, and the change in glacial ice is tracked as best we can, but there’s no global estimate for anything in between. A new study led by the University of Calgary’s Dan Shugar fills in that gap by assessing meltwater lakes near glaciers—and confirms it doesn’t affect the sea level math much.

As was the case with a recent study of ice fractures in Antarctica, the primary challenge here is labor. Finding and mapping every glacial lake in satellite images would be a herculean lift—it has to be automated to be practical. So the researchers grabbed some 255,000 satellite images of glacial areas between 1990 and 2018 and turned to computerized detection to outline each lake. They then relied on an average estimate for the relationship between a lake’s surface area and volume in bodies like these to calculate changes over time based on the lake outlines.