Study finds seawater under Thwaites Glacier doubles sea-level threat

A new study published in Nature Communications estimates that Thwaites Glacier in West Antarctica could contribute up to 1.2 inches (30 millimeters) of global sea-level rise by 2100, even without additional climate warming. The findings, led by glaciologists from the University of California and NASA’s Jet Propulsion Laboratory, suggest the glacier’s threat to coastal areas is roughly double previous estimates.

Grounding Zone Dynamics

The study focuses on the "grounding zone," the area where ice transitions from resting on bedrock to floating on the ocean. Traditional models treated this boundary as a narrow, stable line. However, satellite radar data from the ICEYE constellation revealed that the grounding zone is several kilometres wide and shifts with the tides. This movement allows pressurized seawater to penetrate beneath the glacier’s grounded ice, lifting it and carrying ocean heat farther inland.

Eric Rignot, a professor of Earth system science at the University of California, Irvine, and co-author of the study, noted the significance of these findings. "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," Rignot said in a statement. "Our new model with more complete physics is able to match the record and then produces projections that are twice as large as before."

Model Projections and Uncertainty

The research team used the Ice-sheet and Sea-level System Model (ISSM) to simulate the glacier’s behavior. By incorporating a grounding zone that allows ocean melting to reach beneath the grounded ice, the model reproduced satellite observations of the glacier’s retreat, thinning, and acceleration over the past 20 years.

The study projects a 30-millimeter rise with an uncertainty of about 6 millimeters. This figure contrasts with the average of 15.2 millimeters projected by the international ISMIP6 model ensemble under the same conditions. The new model indicates that the glacier’s main trunk is currently held back by the Mouginot Ridge, a seafloor feature about 950 metres below sea level. According to the study, there is about a 60% chance the glacier slips off this ridge before the end of the century in simulations that best match current radar data. If this occurs, the seafloor deepens inland, potentially accelerating ice loss.

Limitations and Future Risks

The authors emphasize that the 30-millimeter projection is a lower-bound scenario. It assumes the ocean and climate remain at their 1996 to 2023 average, excluding further warming or changes in warm water layers that could increase melting. The model also simplifies certain factors, such as holding the width of the grounding zone fixed and ignoring iceberg calving.

Despite these limitations, the study highlights a specific vulnerability. "The Thwaites main trunk is being temporarily stabilized by the Mouginot Ridge," said Mattia Poinelli, the study’s lead author. The researchers argue that actively melting grounding zones must be integrated into regional and continental ice-sheet models to improve future predictions.

Why it matters

Thwaites Glacier, often referred to as the "Doomsday Glacier," holds enough ice to raise global sea levels by approximately 65 centimeters if it were to melt completely. The region behind the glacier already accounts for about a third of the ice Antarctica loses. An increase in projected sea-level rise from this single glacier raises the baseline for coastal flooding risks worldwide, affecting high tides and storm surges in the coming decades.

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Sources

• gizmodo.com: Ocean Water Is Seeping Under the Doomsday Glacier—and Its Sea-Level Threat Just Doubled
• martincid.com: Seawater seeping under Thwaites Glacier doubles its 2100 sea-level forecast – Martin Cid Magazine

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.