The Greenland ice sheet is huge, accounting for nearly half of all freshwater in the northern hemisphere. But the rising temperatures on earth are melting them – and the world’s oceans are rising. Therefore, the movements of the ice sheet are closely monitored.
Using extensive satellite measurements, researchers from the Geological Survey of Denmark and Greenland (GEUS) and the Niels Bohr Institute at the University of Copenhagen have conducted a study showing how ice sheet movements appear to be closely linked to meltwater flow beneath the ice.
With the help of artificial intelligence, the researchers analyzed ice movements, which they can now divide into four categories based on movement patterns. According to the researchers behind the study, this information is missing from our understanding of why the speed of ice at the same location can change over time, which is an important piece of knowledge to create more accurate climate models, including for sea-level rises.
“Using large amounts of satellite data and artificial intelligence, we can identify and map general seasonal variations over large parts of the ice sheet margin. Not just for one year, but also for fluctuations over several years. “Our study offers an indirect look at the processes under the ice and the connection with large-scale meltwater. This connection is very important to understand in relation to the warming climate of the future, in which the amount of meltwater will increase,” explains Anne Munck Solgaard, senior researcher at GEUS and lead author of the study, now published in Geophysical Research Letters.
tunnels under the ice
When meltwater reaches the ice floor from the surface, it flows mainly through melted channels to the edge of the ice sheet. Researchers have found that the design of these channels, also known as subglacial drainage pathways, affects the movement of the overlying ice.
If the channels, which act as a kind of drainage system, drain water poorly, the pressure on the bottom increases and reduces friction between the ice and the bottom. This in turn causes the ice to move faster toward the ocean. And vice versa, when the drainage system works, the ice moves more slowly.
According to Anne Munck Solgaard, the drainage system is not a fixed array of pipes or channels of a specific size, but rather pathways that develop during the melting season. They do this because while meltwater can melt larger drainage systems, the ice flow serves to close off systems. As such, the drainage system can alternate between efficient and inefficient.
“This leads to four variations in the speed of the ice that we have detected at different locations on the ice sheet. For example, in the middle of the melting season, when meltwater is plentiful, the rate can slow down because the drainage system suddenly becomes efficient. Or the system remains inefficient and under high pressure. The speed therefore corresponds to the amount of meltwater,” says the senior researcher.
This allowed the researchers to see where the ice on the ice sheet was moving in one way or another throughout the year. They get an insight into what is happening under the ice and can observe how it changes from year to year.
“Our results provide a better understanding of how the ice sheet responds to warmer temperatures and more meltwater, which can help us develop future climate models,” explains Dina Rapp, PhD student and co-author of the study.
Huge amounts of data require artificial intelligence
The researchers used artificial intelligence to recognize and separate movement patterns in many thousands of measurements that very quickly become unmanageable for human analysis. According to Professor Christine Hvidberg from the Niels Bohr Institute, the co-author of the study, intelligent computing power is becoming increasingly necessary.
“In recent years, the amount of freely available satellite data has exploded. They come from ESA’s Sentinel satellites and America’s Landsat. The data allow us to map the speed of the ice in high resolution, both temporally and spatially. That’s great, but it also makes it utterly impossible to get a full picture of ice movement and patterns by manually searching through time series. Here artificial intelligence and a lot of computing power help us to recognize previously undiscovered patterns and connections,” she says.
Since 2016, continuous measurements from ESA’s Sentinel-1 satellites have been used to calculate the movement of the ice sheet as part of the Greenland Ice Sheet Monitoring Program (PROMICE).
Find current data
The large amounts of data measured from space were collected using synthetic aperture radar (SAR) from the European Space Agency’s Sentinel-1 satellites. The data has been coupled with measurements from PROMICE weather stations located on the ice itself and, together with measurements of melting, provide the best basis for understanding future climate impacts, including global sea level rise. Ice velocity data is collected every 12 days for high detail velocity maps, 500 x 500 meters, for the entire ice sheet (maps available at https://dataverse.geus.dk/dataverse/Ice_velocity). Weather station readings and daily ice sheet melting estimates are available at promice.org.
