The Florida-sized Thwaites Glacier in West Antarctica is melting in a way that could mean its impacts on global sea level rise are double current estimates, threatening to drive global sea levels up by 1.2 inches by 2100 even without further climate warming. Researchers from the University of California, Irvine and NASA’s Jet Propulsion Laboratory found that seawater flushes deep beneath the ice, accelerating the unpinning of the glacier from underwater ridges.
How Tidal Pumping Accelerates Sub-Ice Melting
For decades, standard ice sheet models tended to view the grounding line—the transition point where grounded ice begins to float on the ocean—as a fixed and stable boundary. Satellite observations, however, revealed a mismatch with those traditional computer simulations. Researchers using synthetic aperture radar data from Finland’s ICEYE satellite constellation tracked fluctuations along the glacier’s main trunk. The data shows that the grounding line functions instead as a wide grounding zone. Seawater constantly flushes in and out here through tidal pumping, lifting and lowering the thick ice.
The Thwaites Glacier in Antarctica is regularly portrayed as a likely source of an imminent 3-metre rise in ocean levels, inundating coastal cities worldwide.But such dramatic speculation is misleading and backed by neither physics nor reality. The 3-metre figure only comes… pic.twitter.com/3d5Fcp5oPv
This dynamic introduces pressurized seawater miles beneath the grounded ice sheet. Ocean heat penetrates deep inland, driving vigorous base melting. “Our new model with more complete physics is able to match the record and then produces projections that are twice as large as before,” said Eric Rignot, a professor of Earth system science at the University of California, Irvine, and co-author of the study published in Nature Communications.
The Risk of Unpinning Along the Mouginot Ridge
Thwaites rests on bedrock that deepens inland, exposing more ice to warm water as the retreat progresses. Underwater topography complicates this flow, featuring two key ridges that act as anchors, pinning the ice back and slowing its descent into the ocean. The melting processes inside the grounding zone are accelerating the unpinning of the ice from the Mouginot Ridge. The study calculates a 60% probability that it will be unpinned before the end of the century. Once unpinned, the ice is likely to retreat rapidly down the downward-sloping bedrock toward the next major ridge.
What Remains Unknown Beneath the Ice
While the updated ice sheet models align much closer with satellite observations, direct data from the sub-glacial environment remain scarce. The environment beneath Thwaites is exceptionally difficult to access, leaving significant gaps in how scientists understand the full physics of grounding zone melting processes. More research is required to secure confident long-term predictions. To bridge this observational gap, the research team is planning to travel there in 2028 to deploy specialized instruments capable of documenting the flushing mechanics of seawater directly at the grounding line.
