The elephant seals that sent data back from underneath Antarctic ice hadn't exactly volunteered for the task—the sensors were glued to their heads. But it was for a good cause. By taking advantage of animals much better equipped to study frigid polar waters than we humans are, climate scientists collected valuable observations. They even got a rare piece of good news: Some ice shelves aren't melting as fast as we thought.
During the Antarctic winter, "harsh climate, strong sea ice cover and permanent darkness put serious limitations" on the ocean sampling researchers can do, says Tore Hattermann of the Norwegian Polar Institute. That's why researchers from around the world are participating in a program called Marine Mammals Exploring the Oceans Pole to Pole (MEOP). Attaching instruments to various kinds of deep-diving seals lets scientists gather ocean data from places that are more hospitable to animals with blubber.
Hattermann and his colleagues used data from the MEOP's elephant seal brigade to enhance their study of melting under an Antarctic ice shelf. About half of the continent's coastline carries ice shelves, floating glaciers that jut out over the shallow part of the ocean. Warm water from the deeper ocean that gets pushed up under these shelves "has an enormous potential to melt the glacial ice," Hattermann says. (To be clear, what polar researchers call "warm" water is just one degree Celsius above freezing.) The melting of this ice can lead to melting of ice on the Antarctic continent itself—which would add to the rising sea level.
So scientists are eager to know just how much ice these shelves are losing. Since they can't very well put a hundred-mile-long block of ice on a scale, they rely on models that predict the movement of warmer and colder water currents underneath the shelves.
The Norwegian team drilled three holes into the Fimbul Ice Shelf, one of the largest ice shelves on Antarctica. It took an average of 230 meters of drilling to break through the shelf; then they sent instruments another several hundred meters down into the ocean below.
To two years' worth of data from these underwater sensors, the researchers added information collected by nine MEOP elephant seals that happened to have spent some quality time around the Fimbul Ice Shelf. For nine months, these animals swam and dove through the waters the team was interested in, while the sensors stuck to their heads recorded their depth as well as the temperature and conductivity of the water. "The seals just loved it there and stayed around for the entire winter," Hattermann says. This gave the researchers a seal's-eye view of how cold and warm water currents moved during different seasons.
What they saw was less warm water traveling under the ice shelf than previous models had predicted. That means less melting. Based on the cold water they saw underneath it most of the time, the ice sheet may not even be losing mass at all.
Hattermann says it's no surprise to oceanographers that their models need honing. The factors they have to account for are incredibly complicated; in this case, for example, there are small waves and eddies that travel within larger currents and are affected differently by the earth's rotation depending on their latitude. Now that they've collected real observations from the underside of an Antarctic ice shelf, researchers can update their models with a little more optimism.
Just because the news from Fimbul was good, though, doesn't mean it's good all around. Senior author Lars Smedsrud of the Bjerknes Centre for Climate Research says that Fimbul is a typical ice shelf for East Antarctica, so the findings there may apply to similar ice shelves. But he cautions that West Antarctica is a different story. (If you're wondering how to find "east" and "west" on a continent where every direction is north, the two sides are divided by a long mountain range and roughly line up with the Eastern and Western Hemispheres.)
"In West Antarctica there is rapid ice loss ongoing," Smedsrud says. "Hard evidence on why this occurs is still not clear," though the melting of ice shelves there seems to be linked to changing wind patterns. It will take more sophisticated models to keep up with how the warming climate is changing the oceans and the poles. While we're building those models, at least we'll have ongoing help from some flippered assistants.
Tore Hattermann, Ole Anders Nøst, Jonathan M. Lilly, & Lars H. Smedsrud (2012). Two years of oceanic observations below the Fimbul Ice Shelf, Antarctica. Geophysical Research Letters, 39 DOI: 10.1029/2012GL051012
Images by Martin Biuw