First Evidence of Key Antarctic Ice Loss Driver Uncovered

For the first time, scientists have uncovered physics-based evidence demonstrating that the thinning of floating ice shelves encircling the edge of mainland Antarctica is causing an increase in ice flow from the land to the sea.

The Antarctic Ice Sheet (AIS)—the largest single mass of ice on Earth, covering about 98 percent of the southern continent—is currently losing mass. And the rate at which this mass loss is contributing to sea-level rise is increasing.

The AIS is encircled by floating, sea-based ice shelves that surround the continent and help hold the land-based ice shelves in place.

Data has shown that in recent years, these floating ice shelves that surround the AIS are thinning—likely as a result of ocean warming or changes in ocean circulation. But while scientists have suspected that this thinning may be responsible for the observed ice loss from the AIS, the hypothesis has not been proven.

Now, researchers have provided evidence that thinning in these floating ice shelves is driving ice loss from the interior of the continent, according to a study published in the journal Geophysical Research Letters.

A team of scientists led by Hilmar Gudmundsson from Northumbria University in the U.K. examined continent-wide satellite measurements taken between 1994 and 2017, with a particular focus on what's known as the "grounding line"—the point where the land-based ice sheets meet the floating, sea-based ice shelves.

The team also used advanced ice-flow models and compared this data with the changes seen in the satellite images over the last quarter of a century. When the results were compared the scientists say they found "striking and robust" similarities in the pattern of ice flowing from the ice sheet into the ocean.

"I found it striking how well our modeled changes agree with the pattern of observed mass loss," Gudmundsson said. "There are other processes in play as well, but we can now state firmly that the observed changes in ice-shelves do cause significant changes over the grounded ice, speeding up its flow into the ocean."

Antarctica map
A map of Antarctica. Northumbria University

According to the researchers, one of the key findings of the study was the fact that the thinning of the floating ice shelves led to an almost immediate loss of ice from the interior into the ocean.

"One of the most important lessons from this study is that the impact is felt without any delay," Gudmundsson said. "Generally, we distinguish between an instantaneous response or a delayed, transient response. Our study shows the thinning of the ice shelves results in a significant instantaneous response to ice flow and ongoing mass loss. This means that we are not protected against the impact of the Antarctic Ice Sheet on global sea levels by a long response time."

"This study closes an important hole in our understanding. Lack of data and limitations in modeling previously made it challenging to quantify the importance of ocean-induced changes as a driver for ongoing mass loss, but we have now shown that the observed ice-shelf changes do indeed impact on upstream flow significantly."

According to Fernando Paolo from NASA's Jet Propulsion Laboratory, the latest findings have significant implications for our understanding of ice mass loss in Antarctica.

"It is striking how far inland the changes in ice shelves can impact the ice sheet flow," he said in a statement. "Since we now know that shrinking ice shelves are directly responsible for increases in ice discharge to the ocean, it is important that we keep monitoring them to watch how they evolve."