Understanding how ice sheets grow, move, and melt is essential for predicting future sea level rise. But reconstructing the history of ice sheets—especially during the Last Glacial Maximum (~21,000 years ago) and earlier periods—requires more than just studying ice. It also demands a deep look below Earth’s surface, into the slow, viscous flow of the mantle.
Ice sheet dynamics refer to the physical processes that govern how ice flows over land. Ice moves outward from thick central regions toward thinner margins, driven by gravity and internal deformation. Key processes include:
- Internal deformation of ice
- Basal sliding over bedrock or water
- Ice shelf dynamics at marine margins
Modern tools like satellite altimetry, radar, and GPS help monitor changes in ice sheets like those in Greenland and Antarctica in real-time. But to know how today’s trends compare to the past, scientists use ice sheet reconstructions.
Reconstruction involves piecing together ice extent and thickness over time using:
- Geological evidence (e.g. moraines, glacial erratics)
- Sea level markers (e.g. coral terraces)
- Isostatic rebound data (how land uplifted after deglaciation)
- This is where mantle viscosity plays a starring role.
When an ice sheet grows, its weight pushes down on the Earth’s crust. When it melts, the crust rebounds—a process called glacial isostatic adjustment (GIA). But the speed and shape of that rebound depends on how viscous the mantle is beneath.
Think of it like pressing and releasing a sponge in honey versus water. The more viscous the mantle, the slower and broader the rebound.
Higher mantle viscosity = slower rebound and wider sea level fingerprint
Mantle viscosity is not uniform. Under old, stable cratons like Canada or Scandinavia, it can be extremely high (~10²² Pa·s), while under tectonically active regions like West Antarctica, it’s much lower (~10²0 Pa·s). These differences must be factored into both past ice sheet reconstructions and sea level rise projections.
If we get mantle viscosity wrong, we may misestimate ice volume or misinterpret regional sea level change.
Research groups like those behind ICE-6G/7G (Peltier) and the ANU GIA models (Lambeck) rely on matching sea level data with mantle models to iteratively improve reconstructions.
Modern GIA models now use 3D Earth structures derived from seismic tomography to get more accurate regional rebound predictions.
Ice sheets don’t just flow—they press, deform, and reshape the solid Earth. To reconstruct their history and forecast their future, scientists must account for both what’s above and beneath the surface. Mantle viscosity is the hidden hand behind sea level signals, and understanding it is key to solving the climate puzzle.