An enormous Antarctic ice shelf is melting slower than scientists previously thought, and they wouldn't have been able to figure out the real rate of melting without the help of elephant seals.
The Fimbul Ice Shelf, located along eastern Antarctica in the Weddell Sea, is the sixth-largest of the 43 ice shelves that dapple Antarctica's perimeter. Ice shelves are floating chunks of ice that act as icy doorstops for the glaciers that flow into them. If an ice shelf is melting rapidly, the glacier behind it may flow faster into the sea, contributing to sea level rise.
It's particularly important to know whether or not the Fimbul Ice Shelf is melting because of both its size and proximity to the East Antarctic Ice Sheet, the largest ice sheet on Earth. If that ice sheet melted, the water it generated could lead to extreme changes in sea level.
Computer models had previously showed significant melting of the Fimbul Ice Shelf. Scientists sought to check the model by taking direct measurements around the ice shelf.
Drilling and elephant seals
Scientists drilled several deep holes into the shelf, which spans an arearoughly twice the size of New Jersey, to directly assess how quickly the ice is melting. This provided them with a partial understanding of what was going on; namely that water there was colder than expected by previous models, said Norwegian Polar Institute researcher Tore Hattermann in a statement.
But to untangle the web of complicated processes that govern melting, the scientists needed a detailed record of annual water cycles and circulation around eastern Antarctica, where the ice shelf is located.
Enter nine male elephant seals outfitted with sensors that measure salinity, temperature and depth. The sensors were attached to the seal by a different research group from the same institution in a separate study, but it turned out the migrating seals gathered just the data need to fill the missing blanks about the Fimbul Ice Shelf. [Images: Antarctic Seals Go Where Scientists Can't]
The seal's trek took them from Bouvet Island, in the middle of the Southern Ocean, to the outskirts of the ice shelf, a distance of 1,000 miles (1,600 kilometers), which was a longer distance than expected for the blubbery beasts.
"Nobody was expecting that these seals from Bouvet Island would swim straight to the Antarctic and stay along the Fimbul Ice Shelf for the entire winter," Hattermann said. "But, this behavior certainly provided an impressive and unique data set."
From the "seal data," the scientists accumulated enough knowledge concerning the area's water circulation and how it changes over the seasons to construct the most complete picture of how the Fimbul Ice Shelf is melting — or freezing — from the bottom up.
Past studies, which were based on computer models without any direct data for comparison or guidance, overestimated the water temperatures and extent of melting beneath the ice shelf. This led to the misconception that the ice shelf is losing mass at a faster rate than it is gaining mass, Hattermann said. The drill and seal measurements were corroborated by satellite measurements.
Because wind patterns and water cycles are similar for large parts of eastern Antarctica, Hattermann said, his team's results could help predict the next time when a section of the Fimbul Ice Shelf, or other ice shelves along the eastern coast of Antarctica, may break off.