Erosion from beneath could lead to more sea-level rise
Oceans warming under a thickening blanket of greenhouse gases are licking at the edge of Antarctica and carving new channels in the bottom of ice shelves all around the frozen continent, researchers said this week in a new study led by scientists with the National Snow and Ice Data Center.
Those channels, characterized as “upside-down rivers” by the scientists, may make the ice shelves more prone to collapsing, which could speed up the flow of ice and the increase the rate of sea-level rise. Overall, some Antarctic ice sheets have thinned by about 18 percent and the rate of melting is accelerating, other research shows.
The findings, published in Nature Geoscience, are based on detailed photography and laser measurements showing that the basal channels also leave traces on the surface of the ice sheets.
“In at least some cases these channels weaken the ice shelves, making them more vulnerable to disintegration,” said Karen Alley, a graduate research assistant at NSIDC and lead author of the study. Alley is also a Ph.D. student in the University of Colorado Boulder’s Department of Geological Sciences.
Ice shelves form over the course of thousands of years but can crumble quickly — within a few weeks, as some recent dramatic examples have shown. The ice sheets flowing off the continent are often pinned against islands, peninsulas, and bedrock, which slows the flow. As more of those pinning points are lost, ice shelves are likely to disintegrate more quickly.
Other studies have suggested that the loss of relatively small sections of Antarctic ice sheets could have a global domino effect, leading to a sudden surge in sea level rise. NASA scientists recently looked at the future of the Larsen Ice Shelf, and
“Ice shelves are really vulnerable parts of the ice sheet, because climate change hits them from above and below,” said Ted Scambos, NSIDC lead scientist and study co-author. “They are really important in braking the ice flow to the ocean.”
The warm currents tracked by the study form buoyant plumes and flow along the underside of an ice shelf, carving channels that can be tens of miles long, and up to 800 feet deep, leaving a visible depression in the relatively smooth ice surface.
Alley and her colleagues mapped the locations of these depressions all around the Antarctic continent using satellite imagery, as well as radar data that images the channels through the ice, mapping the shape of the ice-ocean boundary.
The mapping shows that basal channels have a tendency to form along the edges of islands and peninsulas, which are already weak areas on ice shelves. The team observed two locations where ice shelves are fracturing along basal channels, clear evidence that basal channel presence can weaken ice shelves to the point of breaking in vulnerable areas.
While no ice shelves have completely disintegrated due to carving by basal channels, the study points to the need for more observation and study of these features, said co-author Helen Amanda Fricker of Scripps Institution of Oceanography at UC San Diego.
“It’s feasible that as ocean temperatures around Antarctica continue to rise, melting in basal channels could contribute to increased erosion of ice shelves from below,” Fricker said.
The study, “Impacts of warm water on Antarctic ice shelf stability through basal channel formation,” was led by Alley, who worked with coauthors Ted Scambos of NSIDC and Matthew Siegfried and Helen Amanda Fricker of Scripps Institution of Oceanography, UC San Diego. Their work was funded in part by NASA and the U.S. Geological Survey.