Beneath the Ice, Warm Water Finds Its Way

There is a quiet, relentless kind of power in water. It does not break what it moves against; it finds the small spaces, the unnoticed openings, and it works its way in. For years, scientists have watched the Thwaites Glacier in West Antarctica—often called the "doomsday glacier" because of its role in global sea levels—with growing concern. Now, new research suggests that the ocean is reaching places beneath the ice that were once thought sealed off, and the consequences may be larger than we understood.

A new study led by researchers at the University of California, Irvine and NASA's Jet Propulsion Laboratory has found that warm ocean water is intruding several kilometers beneath the grounded ice of Thwaites Glacier, causing melting that previous models did not account for. The findings, published in Nature Communications, project that Thwaites could contribute up to 30 millimeters of sea-level rise by 2100—twice the estimate of earlier projections .

The key to this revised estimate lies in a concept called the "grounding zone." Traditionally, glaciologists treated the transition between grounded ice and floating ice as a sharp boundary, the "grounding line." But satellite observations from the Finnish ICEYE constellation have revealed that this transition is actually a zone, sometimes several kilometers wide, where seawater pushes beneath the ice and lifts it during tidal cycles .

"We have come to acknowledge a different arrangement beneath Earth's major ocean-terminating glaciers," said lead author Mattia Poinelli, who conducted the research while a postdoctoral scholar at UC Irvine. "Satellite observations demonstrate the existence of a 'grounding zone,' sometimes kilometers wide, where warm ocean water is reaching deep underneath the ice sheets and causing vigorous melting" .

The researchers calibrated their ice sheet model against more than two decades of satellite observations, tracking the glacier's retreat, thinning, and acceleration. They found that only when they included a grounding zone of 2 to 5 kilometers in width could the model reproduce the observed changes. Simulations without such a zone were four times less likely to match the historical record .

Looking forward, the model predicts that the glacier's retreat from a stabilizing seafloor ridge—the Mouginot Ridge—could begin much earlier than previously thought. With a 4 to 6 kilometer grounding zone, there is a 60 percent probability that the glacier will unpin from the ridge by the end of the century, potentially as early as 2038. Once unpinned, the glacier would retreat across a predominantly retrograde seafloor toward the next topographic high .

Thwaites Glacier is roughly the size of Great Britain and already contributes about 4 percent of global sea-level rise. Since 2000, it has lost more than 1,000 billion tons of ice, and its flow speed has doubled in 30 years. The glacier holds enough ice to raise global sea levels by 65 centimeters if it were to completely collapse, and it currently restrains another three meters of sea-level rise lurking within the West Antarctic Ice Sheet .

"We have documented and quantified the impacts of climate change on our planet's sensitive ice sheets for decades, but a mounting realization gained in recent years of what is happening on the undersides of glaciers like Thwaites is leading to an even greater sense of alarm," said co-author Eric Rignot, UC Irvine professor of Earth system science. "Our new model with more complete physics is able to match the record and then produces projections that are twice larger than before" .

The study's authors emphasize that reducing greenhouse gas emissions remains essential, but even with mitigation, higher sea levels are already set in motion by the damage that has been done. The water beneath Thwaites will continue its quiet work, finding its way into spaces we once believed were closed.

The illustrations in this report are AI-generated and serve only as visual aids.

Sources: Nature Communications, University of California Irvine, NASA Jet Propulsion Laboratory, The Conversation