Billions of tons of ice being lost in West Antarctica each year is causing the region to be pushed sideways by sturdier bedrock in the East Antarctica region.

Satellite measurements of the continent reveal that the West Antarctic bedrock is being pushed sideways at a rate of up to 12 millimeters (about 0.5 inches) each year, according to scientists from The Ohio State University, who are presenting their work this week at the 46th Annual Fall Meeting of the American Geophysical Union in San Francisco.

Terry Wilson, professor of earth sciences at Ohio State, said that while it may not seem like much, 12 millimeters is quite dramatic when compared to landmass shifts in other parts of the world.

Wilson said that confirming the sideways movement was not surprising (after all, vertical movement on the continent has been observed since the 1990s), but she said it was revelatory to observe that the bedrock was moving toward regions in Antarctica with the greatest overall ice loss.

"From computer models, we knew that the bedrock should rebound as the weight of ice on top of it goes away," Wilson said. "But the rock should spread out from the site where the ice used to be. Instead, we see movement toward places where there was the most ice loss."

By using seismic sensors to explore the dynamics of this Antarctic bedrock movement, Wilson and her colleagues were able to determine that the mantle regions between the east and west parts of the continent were very different. West Antarctica contains warmer, softer rock than East Antarctica, which is characterized by colder, harder bedrock.

Wilson's colleague Stephanie Konfal, who works as a research associate with POLENET, the international operation that placed the seismic sensors, noted that the sideways movement runs perpendicular to the boundary between the soft and hard bedrock. She likened the process to a pot of honey.

"If you imagine that you have warm spots and cold spots in the honey, so that some of it is soft and some is hard and if you press down on the surface of the honey with a spoon, the honey will move away from the spoon, but the movement won't be uniform. The hard spots will push into the soft spots. And when you take the spoon away, the soft honey won't uniformly flow back up to fill the void, because the hard honey is still pushing on it," she said.

Another way to frame the picture is that ice compressed the soft bedrock in West Antarctica, but that it is not being filled back in uniformly because of ice loss in the West and because the East is pushing the bedrock sideways.

"We're witnessing expected movements being reversed, so we know we really need computer models that can take lateral changes in mantle properties into account," Konfal said.

Wilson noted these extreme differences in bedrock properties are not seen anywhere else on Earth where glacial rebounding is occurring.

"We figured Antarctica would be different," she said. "We just didn't know how different."