The rapid retreat of Thwaites Glacier in West Antarctica appears to be driven by different processes under its floating ice shelf than researchers previously understood, a team of scientists has concluded. Its assessment is based on novel observations from where the ice enters the ocean—these show that while melting beneath much of the ice shelf is weaker than expected, melting in cracks and crevasses is much faster. Significantly, despite the suppressed melting, the glacier is still retreating, the researchers note.
“By adding in new observations of incredibly high melting on the western side of Thwaites, a larger and more complete picture of the interaction of the glacier with the world ocean is emerging,” explains David Holland, director of New York University’s Fluid Dynamics Laboratory and NYU Abu Dhabi’s Center for Global Sea Level Change, who is the lead U.S. principal investigator for the project. “The melt rates on the western side are the highest seen anywhere in Antarctica to date and suggests the glacier may now be in retreat."
The findings, reported in two papers in the journal Nature, provide a vital step forward in understanding how the glacier—the size of the state of Florida—is contributing to future sea-level rise. Specifically, the results show that although melting has increased beneath the floating ice shelf, the present rate of melting is slower than many computer models currently estimate.
A layer of fresher water between the bottom of the ice shelf and the underlying ocean slows the rate of melting along flat parts of the ice shelf. Surprisingly, however, the melting had formed stair-case-like topography across the bottom of the ice shelf. In these areas, as well as in cracks in the ice, rapid melting is occurring.
Thwaites Glacier is one of the fastest changing glaciers in Antarctica: the grounding zone —the point where it meets the seafloor—has retreated 14 kilometers, or more than eight miles, since the late 1990s. Much of the ice sheet is below sea level and susceptible to rapid, irreversible ice loss that could raise global sea-level by over half a meter within centuries.
The new data were collected as part of the MELT project, one of the projects in the U.K.-U.S. International Thwaites Glacier Collaboration, one of the largest international field campaigns ever undertaken in Antarctica. The MELT team undertook observations of the grounding line beneath the Thwaites Eastern Ice Shelf in order to understand how the ice and ocean interacts in this critical region.