Glaciers turn out to be quite ‘spongy’. And that means that the famous Antarctic and Greenland ice sheets have higher densities.

Glacier ice is usually considered brittle. You can drill a hole in an ice sheet – just like a rock – and glaciers erupt and calve, leaving vertical ice cliffs behind. A new study shows, however, that glaciers are also somewhat ‘compressible’ or ‘spongy’. And that’s good news. Because this softer ice cream also means more ice at the same time.

Higher Density

Researchers discover in a new study that ice is compressed across the vast expanse of an ice sheet — think Antarctica or Greenland. And that means a higher density. “It’s like finding hidden ice,” said study researcher Brad Lipovsky. “In a way, we discovered a large chunk of missing ice that hadn’t been properly accounted for.”

Glaciers
It’s no secret that glaciers are melting like the weeds right now. For example, we have known for some time that glaciers have been declining rapidly since the mid-20th century. In fact, almost all of the world’s glaciers have thinned and lost mass. Between 2000 and 2019, Earth’s glaciers lost an average of 267 megatons (billion tons) of ice per year. Moreover, the glaciers also appear to be melting faster and faster during this period. For example, between 2000 and 2004, the glaciers lost 227 gigatons of ice per year, while between 2015 and 2019 no less than 298 gigatons of ice melted.

Because the ice is compressed, there is more gravity and therefore the surface is slightly lower. The researchers calculate that on average over the entire Antarctic ice sheet, the surface is about 0.7 meters lower, which amounts to 30,200 gigatons of extra ice. For Greenland, compression lowers the surface by an average of 0.8 meters, which is equivalent to 3000 gigatons of ice.

Thermal Compression

In addition, the researchers explain that the temperature of a glacier increases with depth. It means we find colder ice near the surface of an ice sheet. Thermal compression then causes the density of this colder ice to increase. This makes this ice more flattened.

0.2 percent

All in all, the researchers show that the Earth contains – albeit only slightly – more ice than previously thought. Together, the combined effects of gravity and thermal compression add about 0.2 percent to the ice sheet’s total mass. While that may sound like only a minor increase, it’s important that we keep this in mind. For example, it will help make better predictions about how glaciers change over time and encouraged by climate change.

Water

The extra ice also means a higher water content at the same time. But this probably doesn’t matter for future sea level rise, the researchers suspect. “In the worst and highly unlikely event that all the glaciers on the planet melt, only 20 centimeters will be added to the projected sea level rise of 80 meters,” Lipovsky said.

Measurements

However, the findings do influence measurements of glacier heights. Because they can change during the seasons. In the winter the glaciers are weighted down with fresh snow, while in the summer much of that snow flows away again. Such seasonal measurements are used to closely monitor the changes that glaciers are undergoing.

However, by including the ‘compressibility’ of the ice in models from now on, we will get a better picture of how large ice sheets respond to climate change. And so we will begin to better understand how the Antarctic and Greenland ice sheets will fare in the future. “I hope it will be a correction that will be taken into account more often,” concludes Lipovsky.