In recent years, warm winds have caused winter temperatures on the Antarctic Peninsula to spike well above freezing. The winds have spurred major melt, causing lakes to form on ice sheets that can eventually accelerate their collapse. Oh, and climate change could make the conditions that spurred the winds worse. Great!
These insights, which come courtesy of a recent study in Geophysical Research Letters, are an “unexpected side-result to a science project” according to Peter Kuipers Munneke, an ice research at Utrecht University who led the study.
He told Earther that initially, scientists wanted to gather information on surface melt in all seasons on the Larsen C ice shelf, which sits at the tip of the Antarctic Peninsula (you may remember it as the ice shelf the calved a trillion-ton iceberg last summer). Its former neighbor, Larsen B, collapsed in 2002 after meltwater pooled on the surface, causing it to essentially cave in on itself.
Several years back, Kuipers Munneke and his colleagues wanted to know if a similar fate would befall Larsen C. So they set up a weather station in Cabinet Inlet in 2015, a location near where the greatest melt was occurring on Larsen C, and gathered a few years worth of data.
“Examination of the data revealed, to our surprise, that temperatures in winter were so high that intense melt occurred at the surface,” he said. “State-of-the-art satellite imagery from the new Sentinel satellites from ESA confirmed the presence of melt lakes in winter.”
The melt was driven by powerful, warm winds called foehn winds (that’s German for hairdryer, by the way). They occur when cool, moist air climbs one side of any mountain range (in this case, those that rise above the Antarctic Peninsula) before tumbling down the other side. As they pick up speed, they release energy they’ve picked up on their travels in the form of heat. And it turns out that even in Antarctic winter, there’s a lot of heat to release.
The weather station showed that surface melt occurred in every month except July, the dead of austral winter. The biggest melt episode occurred from May 25-30, 2016 when foehn winds caused temperatures to reach up to 55 degrees Fahrenheit (13 degrees Celsius) at the ice’s surface.
“First I thought the instruments needed a large correction for such high temperatures,” Kuipers Munneke said. “But the corrections were only minor, and the satellite images showing the lakes in winter confirmed that temperature must have been quite high for a few days.”
Those satellites images revealed widespread melt ponds not just at Cabinet Inlet, but on other parts of the ice shelf. The blasts of warm air also rippled well below the surface of the firn layer of uncompacted snow and ice that covers Antarctica, with melt occurring nearly 10 feet below the surface. Overall, the scientists found that in Cabinet Inlet, up to 23 percent of all observed surface melt between 2015-17 was driven by these foehn wind episodes.
While the winds themselves have natural causes, there’s evidence that climate change will make them worse . In Antarctica, they’re in part tied to a pattern known as the Southern Annular Mode, which describes where a band of westerly winds is located. In its negative phase, it’s closer to the equator while in its positive phase, it tends to be closer to Antarctica. When the Southern Annular Mode is positive, it increases the odds of foehn wind events.
And wouldn’t you know it, some research indicates climate change could to push the mode into the positive phase more often if emissions continue on their current trend, meaning that these wild wintertime melt events could occur more regularly as well. So, with current emissions trends fully expected to continue, don’t forget to bring pack galoshes on your next wintertime expedition to Antarctica.
