‘It’s melting faster each time we measure’
By Summit Voice
FRISCO — While the massive ice cap covering much of Antarctica isn’t likely to melt down anytime soon, the fringes of the frozen continent are showing signs of wear and tear as the planet heats up.
Scientists making long-term measurements of permafrost in the McMurdo Dry Valleys region say permafrost is melting at an accelerating rate. Between 2001 and 2012, the rate rose to about 10 times the valley’s average during the present geologic epoch.
“The big tell here is that the ice is vanishing — it’s melting faster each time we measure,” said Joseph Levy, a research associate at The University of Texas at Austin’s Institute for Geophysics. “This is a dramatic shift from recent history,” Levy said, explaining there are no signs in the geologic record that the valley’s ground ice has retreated similarly in the past.
The melt rates are comparable with the Arctic, where accelerated melting of permafrost has become a regularly recurring phenomenon, and the change could offer a preview of melting permafrost in other parts of a warming Antarctic continent. The research was published July 24 in Scientific Reports.
Scientists previously thought that seasonal melting and refreezing were about equal, without any loss of the valley’s overall mass of ground ice.
Instead, Levy documented through LIDAR and time-lapse photography a rapid retreat of ground ice in Garwood Valley, similar to the lower rates of permafrost melt observed in the coastal Arctic and Tibet.
The melting isn’t due to warming regional temperatures. Temperatures in the Dry Valleys region cooled between 1986 and 2000, followed by a period of stable temperatures. Instead, the scientists suspect the melting is driven by increases in incoming solar radiation, as changing weather patterns lead to more sunny days in the area.
Sunlight tends to bounce off the white, reflective surfaces of glaciers and ice sheets, but the darker surfaces of dirty ground ice can absorb greater amounts of solar radiation. Thick layers of sediment tend to insulate deeply buried ground ice from sunlight and inhibit melting. But thin sediment layers have the opposite effect, effectively cooking the nearby ice and accelerating melt rates.
As the ground ice melts, the frozen landscape sinks and buckles, creating what scientists describe as “retrogressive thaw slumps.” An acceleration in the prevalence of such slumps has been well documented in the Arctic and other permafrost regions, but not in Antarctica.
Ground ice is more prevalent in the Arctic than in Antarctica, where glaciers and ice sheets dominate the landscape. In contrast to glaciers and ice sheets, which sit on the ground, ground ice sits in the ground, mixed with frozen soil or buried under layers of sediment. Antarctica’s Dry Valleys contain some of the continent’s largest stretches of ground ice, along the coast of the Ross Sea.
Levy’s research shows that even under the stable temperature conditions of the Dry Valleys, recent increases in sunlight are leading to Arctic-like slump conditions.
If Antarctica warms as predicted during the coming century, the melting and slumping could become that much more dramatic as warmer air temperatures combine with sunlight-driven melting to thaw ground ice even more quickly.
Ground ice is not the major component of Antarctica’s vast reserves of frozen water, but there are major expanses of ground ice in the Dry Valleys, the Antarctic Peninsula and the continent’s ice-free islands.
Garwood Valley could tell the story of what will happen in these “coastal thaw zones,” says Levy.
“There’s a lot of buried ice in these low-elevation coastal regions, and it is primed to melt.”