It’s official! East Antarctica is pushing West Antarctica around.

West Antarctica is losing billions of tonnes of ice per year and its softer mantle rock is being nudged westward by the harder mantle beneath East Antarctica, scientists say.

The discovery was made by researchers led by The Ohio State University, who have recorded GPS measurements that show West Antarctic bedrock is being pushed sideways at rates up to about twelve millimetres — about half an inch — per year.

This movement is important for understanding current ice loss on the continent, and predicting future ice loss.

Half an inch doesn’t sound like a lot, but it’s actually quite dramatic compared to other areas of the planet, said Terry Wilson, professor of earth sciences at Ohio State.

Wilson said scientists were surprised to find the bedrock moving towards regions of greatest 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,” said Wilson.

By timing how fast seismic waves pass through the Earth under Antarctica, the researchers were able to determine that the mantle regions beneath east and west are very different.

Stephanie Konfal, a research associate with POLENET, pointed out that where the transition is most pronounced, the sideways movement runs perpendicular to the boundary between the two types of mantle.

Some ice has melted away, but the soft mantle isn’t filling back in uniformly, because East Antarctica’s harder mantle is pushing it sideways. The crust is just along for the ride, researchers said.

This finding is significant because we use these crustal motions to understand ice loss, Konfal said.

“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,” said Konfal.

Wilson said that such extreme differences in mantle properties are not seen elsewhere on the planet where glacial rebound is occurring.

“We figured Antarctica would be different. We just didn’t know how different,” she said.

The findings were presented at the American Geophysical Union meeting in San Francisco.

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