Beneath the massive ice of Thwaites Glacier in West Antarctica, something is happening that no climate model accounts for. Warm seawater, pushed by ocean tides, is forcing its way kilometers inland under ice that sits on solid bedrock, melting the glacier from below in pulses that repeat with each tidal cycle. A study published in the Proceedings of the National Academy of Sciences captured these intrusions using daily satellite radar observations between March and June 2023, and the researchers behind it say the process could destabilize one of the most watched ice systems on Earth far sooner than current projections suggest.
Thwaites is often called the “Doomsday Glacier” for good reason. It holds enough ice to raise global sea levels by about 65 centimeters on its own, and its collapse could drag neighboring glaciers with it, potentially unlocking more than three feet of total rise from West Antarctica. The newly documented intrusions represent a mechanism that sits entirely outside the physics built into standard ice sheet models, meaning the tools scientists and policymakers rely on for planning may be systematically underestimating how quickly the glacier is losing ground.
What satellite radar and underwater robots have revealed
The core finding comes from a team led by Pietro Milillo of the University of Houston, who used the commercial ICEYE radar satellite constellation to take daily snapshots of Thwaites’ grounding zone, the critical boundary where ice lifts off bedrock and begins to float. The radar data showed pressurized seawater repeatedly surging beneath grounded ice, traveling kilometers inland before retreating with the tide. Each intrusion delivers warm water to surfaces that were assumed to be sealed off from the ocean, driving melt in places models treat as stable.
This is not the only window into what is happening beneath Thwaites. The International Thwaites Glacier Collaboration, a joint U.S.-U.K. research effort funded in part by the National Science Foundation, deployed an underwater robot called Icefin through boreholes drilled in the ice. Icefin measured water temperature, salinity, and the shape of the cavity between ice and bedrock, confirming that warm ocean water reaches the ice-bed interface through multiple pathways. Those measurements provide direct, instrument-based evidence that the underside of Thwaites is under sustained thermal attack.
A separate study published in Nature Communications added another layer. Researchers simulated the effects of a 2013 subglacial lake discharge at Thwaites and found that the resulting freshwater pulse could boost average basal melt by roughly 11 gigatons per year, an increase of about 70 percent in their model. Along parts of the grounding line, the simulated melt reached hundreds of meters per year. The finding links the glacier’s internal plumbing, its network of subglacial lakes and drainage channels, directly to the rate at which the ocean erodes its base.
NASA’s MEaSUREs program provides the broader spatial framework. Its grounding zone dataset, built from Landsat, Sentinel-1, ICESat-2, CryoSat-2, and other platforms, maps short-term grounding-zone migration caused by tides across all of Antarctica. That record gives scientists a baseline for measuring how far and how fast the grounding line is retreating, a key indicator of whether the glacier is losing its grip on the bedrock that slows its slide toward the sea.
Where the science is still catching up
The satellite observations of seawater intrusions cover only four months. Whether these events persist year-round, intensify seasonally, or fluctuate over longer cycles has not been established. No multi-year record of tidally driven intrusions at Thwaites exists in the published literature, which means the long-term effect on grounding-line retreat remains an open question.
Melt rates across the glacier are also far from uniform. A study published in Nature found that parts of the Thwaites Eastern Ice Shelf grounding zone show modest melt because a layered water column limits how much heat reaches the ice. Yet the same study concluded that the broader Thwaites system remains primed for retreat. That tension between localized suppression and system-wide instability makes it difficult to project a single trajectory for the glacier.
The role of marine ice-cliff instability, a mechanism in which tall ice cliffs collapse under their own weight after losing the support of floating ice shelves, remains especially contested. A 2016 modeling study by Robert DeConto and David Pollard, published in Nature, showed that this process could produce much higher sea-level contributions than older model generations predicted. But a subsequent reassessment found that the range of possible outcomes is wide and that confidence in the most extreme scenarios is limited. Whether the newly documented seawater intrusions could trigger or accelerate cliff collapse is a question no published study has yet addressed.
Similarly, no peer-reviewed analysis has combined what is known about subglacial lake discharges with research on ice-shelf fracture vulnerability. Scientists have separately quantified which buttressing portions of Antarctic ice shelves could break apart if flooded with meltwater, and other teams have modeled how subglacial freshwater pulses alter basal melt. But the joint effect of these two processes on Thwaites retreat rates remains unstudied.
Sorting strong evidence from projection
Not all of the evidence carries equal weight. The PNAS study on seawater intrusions rests on satellite radar data collected daily over a defined period, making it reproducible and spatially precise. The Icefin measurements provide ground-truth data from beneath the ice itself. These are primary, instrument-based records.
The subglacial lake discharge study sits in a middle tier: it combines observational constraints on lake drainage timing and volume with high-resolution simulations of how freshwater modifies ocean circulation and melt. The modeled response introduces uncertainty, but the physical link between drainage and enhanced basal melt is consistent with established understanding of how buoyant plumes erode ice from below.
Large-scale projections of Thwaites-driven sea level rise carry the most uncertainty. They depend on how models represent poorly understood processes such as ice-cliff failure, crevasse propagation, and feedbacks between ocean circulation and ice-shelf thinning. The Intergovernmental Panel on Climate Change’s most recent assessment report projects up to about 1 meter of global sea level rise by 2100 under high-emission scenarios, but acknowledges that contributions from the West Antarctic Ice Sheet could push totals significantly higher if processes like marine ice-cliff instability prove to be real. The newly documented tidal intrusions add yet another mechanism that most continental-scale models do not incorporate, suggesting some published projections may underestimate the pace of near-term change.
At the same time, stabilizing factors exist. Localized ocean stratification can suppress melt. Bedrock ridges can temporarily pin the grounding line. These features mean the most extreme runaway scenarios are not inevitable. But the balance between destabilizing and stabilizing forces is highly sensitive to relatively small changes in ocean temperature, circulation patterns, and ice geometry, which is why different modeling groups arrive at divergent timelines for the same glacier.
What this means for a world built at sea level
For coastal planners and policymakers, the practical message is not a single revised number for future sea level rise. It is a shift in risk. The discovery of widespread seawater intrusions beneath grounded ice shows that parts of the Antarctic system can respond to ocean forcing more quickly than previously appreciated. That raises the probability of crossing thresholds where retreat becomes difficult to halt on human timescales, even if global emissions eventually decline.
In concrete terms, infrastructure designed around conservative or median sea level projections could face higher-than-anticipated water levels within the lifetime of current investments. Ports, wastewater treatment plants, coastal highways, and low-lying neighborhoods in dozens of countries are already contending with nuisance flooding and worsening storm surge. An additional contribution from Thwaites on the order of tens of centimeters would compound those stresses, especially when layered on top of local land subsidence and regional ocean dynamics.
For researchers, the priorities are clear as of mid-2026. Expanding continuous satellite coverage of the grounding zone, refining maps of the seafloor beneath and in front of Thwaites, and building tidal intrusion physics into ice-ocean models are all essential for narrowing projections. Coordinated field campaigns using autonomous underwater vehicles and additional boreholes can help determine whether the 2023 intrusion events represent a persistent process or an episodic one.
The emerging picture is of a glacier caught between competing forces: warm water probing inland along hidden pathways, structural weaknesses accumulating in its floating extensions, and occasional pockets of relative stability where ocean layering or seafloor topography slows the damage. The latest findings do not guarantee rapid collapse. But they strip away one of the comforting assumptions that underpinned earlier projections: that the ice sitting on bedrock was, at least for now, beyond the ocean’s reach. At Thwaites, it is not.
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*This article was researched with the help of AI, with human editors creating the final content.
