No rest for the ice: Study documents increased movement of ice far into the Greenland Ice Sheet

Published 24-04-2024

Comparisons of new measurements with data from 1959 suggest that ice far from the edge of the Greenland Ice Sheet is more dynamic than expected.

Anja Løkkegaard and William Colgan set up equipment for GPS measurement. (Photo: William Colgan, GEUS.)

Researchers have recorded the velocity (movement) of ice far from the coast in an area at the glacier Sermeq Kujalleq in West Greenland. The measurements show that the ice over 100 km inland from the edge of the ice has increased its velocity by between 5 and 15% since previous measurements in 1959.

The study is published in Communications Earth and Environment.

15% may not sound like much, but the locations of the measurements mean that the study’s results make us rethink our understanding of the ice. Until now, we have believed that the ice masses along the edge of the Greenland Ice Sheet and by the large glaciers are racing cars, while we expect to find more speed bumps the further into the Greenland Ice Sheet we get – but that may not be true at all.

“We know that Sermeq Kujalleq moves at an extremely high speed, and we generally know a lot about movement and acceleration along the edge of the ice, because we have been able to document it. We assumed that the ice in the ice sheet interior would be reacting more slowly, but the new measurements show that this is not the case in that area,” says Anja Løkkegaard, who is a postdoc at GEUS and first author of the research article in which the study is presented.

It is a logistically challenging area to make measurements in, but the GPS measurements can do something that the satellite measurements cannot:

“It is very difficult to operate this far into the ice sheet, but it is important to measure the ice velocities in there via GPS, as the satellite-derived data become less reliable further inland from the coast. With the GPS observations measured far into the Greenland Ice Sheet, we can now see an acceleration of the ice sheet, which the satellites cannot yet register,” says co-author Shfaqat Abbas Khan, who is a professor at DTU Space and has processed the GPS data.

A simplifies map of Greenland in the upper elft corner shows the area in which the researchers did measurements. The area is visible with an overlay of a heatmap og movement. The loactions for GPS measurements are marked.

Above: The eleven black rings with a white dot in the middle show the locations of GPS measurement stations included in the study. The colours show the velocity of ice in a given area. Sermeq Kujalleq lies like a bright red dragon surrounded by orange mist because the velocity here is extremely high. Inside the locations for the measurements, the colour is blue-green because the velocity is much lower. (Figure 1, Ice acceleration and rotation in the Greenland Ice Sheet interior in recent decades, Communications Earth and Environment.)

The study’s results indicate that there are parts of the mechanisms regarding how the ice reacts to e.g. global warming, which we are not yet fully familiar with.

Measurements can often make the difference between our best educated guess and actually knowing something. Knowing something is not the same as knowing why, but it puts us in a better position to ask the relevant questions that can help us understand why the ice behaves the way it does.

“We now have some important data that we are as sure of as we can be. But we’re not sure why the data are like that. Based on the data we have, our best bet is that a mechanism we call creep stability is at play. But it is one of several relevant suggestions,” says Anja Løkkegaard.

Several solid mechanisms are often used to explain why the velocity of ice is higher – it could be meltwater underneath or the formation of steep slopes in the ice. The researchers have investigated whether the unexpected increased velocity of the ice could be due to some of these well-known mechanisms, but none of them can explain the results in this case. Therefore, the authors of the research article refer to a limited form of creep stability as a possible explanation.

Creep stability is a term for the way the ice flows when ice crystals shift in the ice.

So far, creep stability is a purely theoretical explanation. The deformation occurs so far down the ice column that it is difficult to support it with observations – Anja Løkkegaard describes it as an expensive logistical challenge to undertake. But the data would be valuable to add to the pool of knowledge and data that researchers use when they make educated guesses about how the Greenland Ice Sheet reacts to climate change.

“If we can find out with greater certainty why this is happening, we will be able to find out where in the ice it is happening and what it means for the development of the Greenland Ice Sheet in the future,” says Anja Løkkegaard.

It is important to understand how the Greenland Ice Sheet is changing to make more reliable projections of e.g. sea level rise.

The research was supported by Independent Research Fund Denmark via the Sapere Aude project 'Unraveling the response time scales of Greenland’s most critical glacier.'

How they did it: from stick to satellite

The researchers have measured the velocity of the ice along an x- and y-axis (2D) at 11 locations at Sermeq Kujalleq (also known as ‘Ilulissat Glacier’ and ‘Jakobshavn Isbræ’). The locations have been selected because measurements of the velocity of ice were made there in 1959. This gave the researchers something to compare with. In 1959, the measurements were made by placing a stick in the ice and later returning to measure how far the stick had moved. The new measurements were made with GPS. The uncertainties that the researchers have found in the previous measurements have been taken into account in the calculations in the new study.

Photo: Anja Løhhegaard is setting up a GPS measurement station. (Photo: William Colgan, GEUS.)

Photo: William Colgan takes an uplifting selfie after the succesful installment of a GPS measurement station. The researchers are wearing face masks to prevent health issues for the helicopter pilot as the field work was done during the COVID19 pandemic. (Photo: William Colgan, GEUS.)