Researchers create more detailed picture of Greenland ice sheet movement – Zoo House News
- February 13, 2023
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Researchers have found that the movement of Greenland’s glaciers is more complex than previously thought, with deformations in regions of warmer ice that contain small amounts of water accounting for movements often thought to be caused by sliding where the ice meets the underlying bedrock.
The international team of researchers, led by the University of Cambridge, used computer modeling techniques based on previous fiber-optic measurements of the Greenland ice sheet to create a more detailed picture of the behavior of the world’s second largest ice sheet.
Their findings, reported in the journal Science Advances, 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 six-fold since the 1980s and is now the single largest contributor to global sea level rise. About half of this mass loss is from surface runoff of meltwater, while the other half is driven by runoff of ice directly into the ocean through fast-flowing glaciers reaching the sea.
The RESPONDER project, funded by the European Research Council, is studying the dynamics of the Greenland ice sheet using a combination of physical measurements and computer models.
The current research builds on previous observations reported by the RESPONDER team in 2021 using fiber optic cables. In this work, the team found that the temperature of ice sheets does not vary as a gentle gradient, but is far more heterogeneous, with areas of highly localized deformation continuing to warm the ice.
The logs also showed that the ice at the base contains small amounts — up to about two percent — of water. This mixed ice-water layer, called temperate ice, was about eight meters thick in some places on the ice sheet and up to 70 meters thick in other places.
“The addition of even minute amounts of water softens the ice significantly, turning it into a unique material with significantly altered mechanical properties,” said lead author Dr at the University of Bergen. “We wanted to know why the thickness of this layer varies so much, because unless we fully understand it, our models of ice sheet behavior will not fully capture the physical processes occurring in nature.”
‘The textbook view of glacial movement is that it occurs with a clean division of basal slip and internal deformation and that both are well understood,’ said co-author and RESPONDER project leader Professor Poul Christoffersen, who works at SPRI. “But that’s not what we’ve observed when we’ve probed wells with new techniques.” With less detailed observations in the past, it’s been difficult to get a really good picture of how the ice sheet is moving, and even harder to replicate with computer models.”
Law, Christoffersen and their colleagues from the UK, US, Switzerland and France developed a model based on their previous logs that can incorporate any new observations.
Importantly, they explained natural variations in the landscape at the foot of the ice, which in Greenland is full of rocky hills, basins and deep fjords. The researchers found that when a glacier moves over a large obstacle or hillock, a deforming and heating effect occurs, sometimes extending hundreds of meters from the base of the ice sheet. So far, this effect has been omitted from models.
“The stress on the ice base is highest on the tops of these mounds, resulting in more basal slippage,” Law said. “But so far, most models have not accounted for all of these variations in the landscape.”
By incorporating these variations, the model the researchers developed showed that a variable layer of temperate ice forms as the glacier moves across the landscape, regardless of whether the glacier itself is moving quickly or slowly. The thickness of this temperate ice sheet is consistent with previous borehole measurements, but differs significantly from standard modeling methods used to predict sea level rise from ice sheets.
“Because of this hilly landscape, the ice can go from almost completely sliding over its base to almost completely sliding over short distances of just a few kilometers,” Law said. “This directly affects the thermal structure – if you have less basal slip, you have more internal deformation and heating, which can cause the layer of temperate ice to thicken and change the mechanical properties of the ice over a wide range of this temperate basal.” Ice sheet can actually act like a deformation bridge between hills, facilitating the rapid movement of the much colder ice directly above.
Researchers hope to use this improved understanding to create more accurate descriptions of ice movement for the ice sheet models used to predict future sea level rise.
The research was funded in part by the European Union and the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI).