Undersea "Storms" Are Melting Antarctic Glaciers from Below

A team of researchers including oceanographer Lia Siegelman of UC San Diego’s Scripps Institution of Oceanography co-authored a new study that describes storm-like ocean circulation patterns beneath Antarctic ice shelves that are causing aggressive melting, with major implications for global sea-level rise projections. Siegelman collaborated with researchers from UC Irvine, NASA’s Jet Propulsion Laboratory and Dartmouth College on the study. 

The study, published in Nature Geoscience and supported by NASA, is the first to examine ocean-induced ice shelf melting events on shorter timescales — days rather than months or years — according to the researchers. This enabled the team to match “ocean storm” activity with intense ice melt at Thwaites Glacier and Pine Island Glacier in the climate change-threatened Amundsen Sea Embayment in West Antarctica.

"It was very surprising to discover that ‘storm-like’ ocean phenomena could propagate from the open ocean and reach Antarctic ice shelves to contribute to melting the ice from below,” said Siegelman. “Studying these fine-scale ocean phenomena is the next frontier when it comes to the ocean-ice interactions that help us understand ice loss and, ultimately, sea level rise."

The research team used computer models to simulate ocean-ice interactions at 200-meter (656-foot) resolution, which allowed them to capture smaller-scale ocean phenomena. They combined this modeling approach with real-world observations from instruments attached to the seafloor beneath the Thwaites ice shelf called moorings. 

The researchers identified a positive feedback loop between turbulent water masses about 1-10 kilometers (0.6-6 miles) wide and ocean-induced melting: More ice shelf melting generated more ocean turbulence, which in turn caused more ice shelf melting. 

“This positive feedback loop could gain intensity in a warming climate, potentially contributing to sea level rise,” said Siegelman.

The study found that meltwater creates ephemeral processes that transfer additional heat into the seawater near the ice sheet, accelerating melting. These processes may account for nearly one fifth of the variation in underwater melting over time. Extreme undersea “storms” can increase underwater melting by up to three times within hours as these ocean phenomena intrude beneath the ice shelf.

Moorings in the vicinity and floats deployed in another sector of Antarctica corroborated the model’s output with high-resolution real-world measurements, including distinct warming events that matched the magnitude and duration of the events identified by the model.

As Earth warms, these ocean ‘storms’ could become more frequent and intense due to reduced sea ice coverage and longer periods of ice-free conditions near glaciers, with far-reaching implications for ice shelf stability and global sea level rise. The Thwaites and Pine Island glaciers examined in this study make up key chunks of the West Antarctic Ice Sheet, which could raise global sea level by up to 3 meters (10 feet) if it were to collapse.

The study’s findings highlight the need for climate models to account for these smaller scale ocean processes as they attempt to project future ice loss and sea level rise, said Siegelman. 

Eric Rignot, a UC Irvine glaciologist who advised the research team, said the study pointed to an “urgent need to fund and develop better observation tools, including advanced oceangoing robots” that can directly observe and measure these dynamic underwater storms.

In addition to Siegelman of Scripps Oceanography, Mattia Poinelli, a UC Irvine postdoctoral scholar in Earth system science and NASA JPL research affiliate,  and Yoshihiro Nakayama of Dartmouth College co-authored the study.