Warm ocean water pushing beneath Antarctica’s massive Thwaites Glacier is melting its underside far faster than previously understood, potentially doubling its contribution to global sea levels by the end of the century, according to research published in the journal Nature Communications.
Scientists from the University of California, Irvine, and NASA’s Jet Propulsion Laboratory found that the West Antarctic glacier could add up to 1.2 inches to global water levels by 2100. That figure is double previous forecasts and could occur even without further acceleration in planetary warming, researchers reported.
A dynamic grounding zone accelerates melt
Glaciologists have long evaluated glacier stability using the concept of a grounding line, a relatively fixed boundary where an ice mass leaves solid bedrock and begins floating on the ocean. However, satellite observations from the Finnish ICEYE constellation revealed that Thwaites instead features a dynamic grounding zone that can span several miles wide.
In this zone, ocean tides raise and lower the heavy ice in a cycle known as tidal pumping. This action flushes relatively warm, pressurized seawater deep beneath the glacier’s base, driving vigorous subsurface melting that standard climate simulations previously failed to capture, according to the study.
“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,” said lead author Mattia Poinelli, a project scientist at UCLA who conducted the research while at UC Irvine.
Spanning roughly 74,130 square miles in Marie Byrd Land—an expanse roughly the size of Florida or Senegal—Thwaites is the widest glacier on Earth. Its ice loss currently drives about 4 percent of global sea-level rise, shedding approximately 50 billion metric tons of ice annually, researchers noted.
Threat to stabilizing underwater ridges
Because Thwaites rests on bedrock that slopes downward inland, retreating ice exposes increasingly thicker sections to warm marine currents. Currently, the glacier’s main body is held back by underwater bedrock formations, primarily an underwater ridge known as the Mouginot Ridge.
Simulations factoring in a grounding zone between 2.5 and 3.7 miles wide found a 60 percent probability that the glacier will detach, or unpin, from the Mouginot Ridge before 2100. Once unpinned, scientists warned that the glacier would retreat rapidly down the declining seabed toward another formation called the South Ridge.
A complete collapse of Thwaites would raise global seas by more than 2 feet on its own. Because it also blocks the larger West Antarctic ice sheet from sliding into the sea, its eventual loss could ultimately trigger roughly 10 feet of global sea-level rise over coming centuries, threatening low-lying coastal hubs worldwide.
“Most projections to date have struggled to match the rapidity of the mass loss because of missing physics,” co-author Eric Rignot, a professor of Earth system science at UC Irvine, said in statements reported by Phys.org. He noted that incorporating these mechanisms produces projections that heighten the known flooding risks for coastal areas in the coming decades.
Scientific expeditions planned to verify findings
Outside researchers acknowledged the significance of the modeling while calling for direct physical data from the harsh Antarctic environment. Ted Scambos of the University of Colorado Boulder described the results to CNN as a potential major change for sea-level forecasting, but geophysicists cautioned that the environment underneath the ice remains difficult to access and highly complex.
Independent research published in July by the British Antarctic Survey indicated Thwaites will continue shedding ice for at least 150 years under all projected ocean scenarios. To verify what is occurring in the grounding zone, Rignot said a research team plans an expedition to Thwaites in 2028 to install instruments directly beneath the ice shelf to measure tidal water flow.
