New research shows that a Florida-sized block of ice in Western Antarctica called the Thwaites Glacier is sitting on top of large channels that may allow warm ocean water to melt it from the bottom, Carolyn Gramling reports for Science News.
Two new studies, both published in the journal Cryosphere, provide a detailed map of the glacier’s two ice shelf regions and the ocean floor in front of and underneath them. As one of the largest glaciers in Antarctica, the Thwaites Glacier is the subject of close study—if the entire glacier melted, it would cause ocean levels to rise by 25 inches. When the new maps are incorporated into models of Thwaites’ melting, that will show whether the deep trenches might cause the glacier to collapse sooner than previously predicted.
“Understanding that process and how these cavities evolve will be key to understanding how Thwaites and western Antarctica will change in the future,” says British Antarctic Survey aero-geophysicist Tom Jordan to the Guardian’s Jonathan Watts.
In early 2019, Jordan and a team of scientists from the United States and United Kingdom used a combination of aerial and ship-based surveys to gather radar, sonar and gravity measurements around Thwaites Glacier, per Science News. They used the surveys to map the shape of the sea floor in front of the glacier, because that land used to be underneath the glacier so it’s useful as an analogue for the ground currently under the glacier.
Measurements of the sea floor directly beneath the glacier revealed a major channel of sea water more than 2,600 feet deep bringing warm water under the glacier. They also found a network of new, thinner cracks in the ice. These channels wouldn’t be able to carry as much warm water into the glacier and might provide some temporary stability to a retreating glacier, the researchers write in their paper, so the new, more detailed mapping may change computer models’ predictions of how the glacier will retreat.
“Before we did these studies, the assumption was that all the channels are the same, but the new ones are much thinner and more dynamic,” Jordan tells the Guardian. But he adds that “they will get bigger over time.”
Large channels of ocean water can make the glacier melt from underneath. Already, a cavity two-thirds the size of Manhattan has formed in the underside of the Thwaites Glacier, as Julia Jacobs reported for the New York Times early last year.
"Thwaites Glacier itself is probably one of the most significant glaciers in West Antarctica, because it's so large, because we can see it's changing today," Jordan tells Emma Reynolds at CNN.
"And also, we know that its bed dips down, and it gets deeper and deeper underneath the ice sheet, which means that, theoretically, you can get a process called marine ice sheet instability," she adds. "And once it starts to retreat, it will just keep retreating."
Thwaites Glacier is currently losing about 50 billion more tons of ice each year than it receives in snowfall, according to the International Thwaites Glacier Collaboration. Its melting has contributed to four percent of sea level rise so far, and the rate of ice loss from Thwaites and its surrounding glaciers has increased five-fold in the last 30 years, according to a statement by BAS.
Because the source of warm water is a deep channel that runs under the glacier, one might imagine plugging up the channel like filling a tooth cavity. But such a strategy is impractical in a location as remote as Thwaites Glacier, with cavities so large. Jordan tells the Guardian that slowing greenhouse gas emissions and mitigating the effects of climate change would be a more effective solution.
The next step will be to incorporate the new data into simulations of the future of the glacier. “There was so much uncertainty about understanding the ice sheet processes and how the glaciers will over time respond,” Jordan tells CNN, but the new data is a “big step” toward improved models of sea-level rise.