A new study has found that the movement of glaciers in Greenland is more complex than previously thought. The team led by researchers from the University of Cambridge used computer modeling techniques based on earlier fiber-optic measurements from the Greenland Ice Sheet.
Their findings could be used to develop more accurate predictions of how the Greenland Ice Sheet will continue to move in response to climate change.
Mass loss from the Greenland Ice Sheet has increased sixfold since the 1980s and is now the greatest contributor to global sea-level rise. About half of this moss loss is from surface meltwater runoff, while the other half is driven by discharge of ice directly into the ocean by fast-flowing glaciers that reach the sea.
The current research is founded on earlier observations reported by the team from the RESPONDER project in 2021 using fiber-optic cables. They found that the temperature of ice sheets does not vary as a smooth gradient, but is far more heterogeneous, with areas of highly localized deformation warming the ice further.
The borehole measurements also showed that the ice at the base contains small amounts – up to about two percent – of water. In some parts of the ice sheet, this mixed ice-water layer, called temperate ice, was roughly eight meters thick, but in other parts it was up to 70 meters thick.
The researchers developed a model based on their earlier borehole measurements that account for all of the new observations.
Importantly, they accounted for natural variations on the surface at the base of the ice, which, in Greenland, is full of rocky hills, basins and deep fjords. The researchers found that as a glacier moves over a large obstacle or hill, there is a deformation and heating effect which sometimes extends several hundred meters from the base of the ice sheet. Previously, this effect had been omitted in models.
“The stress on the ice base is highest at the tops of these hills, which leads to more basal sliding,” said first author Dr. Robert Law. “But so far most models have not accounted for all of these variations in the landscape.”
“Because of this hilly landscape, the ice can go from sliding across its base almost entirely to hardly sliding at all, over short distances of just a few kilometers,” explained Law. “This directly influences the thermal structure—if you’ve got less basal sliding then you’ve got more internal deformation and heating, which can lead to the layer of temperate ice getting thicker, altering the mechanical properties of the ice over a broad area. This temperate basal ice layer can actually act like a deformation bridge between hills, facilitating the fast motion of the much colder ice directly above it.”
The researchers plan to use this improved understanding to build more accurate descriptions of ice motion for the ice sheet models used in predicting future sea level rise.
https://phys.org/news/2023-02-picture-movement-greenland-ice-sheet.html