Rapidly rising bedrock may help delay Antarctic Ice Sheet collapse

UNIVERSITY PARK, Pa. — The bedrock beneath West Antarctica is rising rapidly in response to the ongoing ice melt of the West Antarctic Ice Sheet (WAIS), according to an international team of researchers. This rapid uplift may help stabilize the ice sheet against catastrophic collapse due to ice loss.

The researchers, including Andrew Nyblade, professor of geosciences, Penn State, recently reported their findings in Science, indicating that their results have important implications for estimating future ice sheet stability and projections of ice mass losses.

“The question is how fast is the climate going to change, because if it continues to rapidly warm, the uplift might not happen fast enough to slow down the collapse of the ice sheet,” said Nyblade.

The weight of glaciers and ice sheets depresses the land beneath them, and as the ice melts, the Earth’s surface rebounds with the reduced load.

“The solid Earth can have a big impact on what could happen to the ice sheet," said Nyblade. “The mantle is pushing up faster than expected and that could help stabilize the ice sheet.”

The region where the ice sheet loses contact with underlying bedrock or sediment and goes afloat is referred to as the grounding line. Most of the WAIS is grounded below sea level, making it susceptible to melting by warming ocean waters flowing beneath the ice sheet.

“The bottom of the ice sheet is below sea level," said Nyblade. "As the Earth pushes back up from underneath, the bottom of the ice rises so it’s harder for seawater to get underneath, slowing the melting process.”

Bedrock’s response to ice mass loss was thought to occur on a time scale of 10,000 years, but the researchers found that the ground under the rapidly melting Amundsen Sea Embayment in West Antarctica is rising at the rapid rate of 1.6 inches per year.

“The rate of the uplift is controlled by the viscosity of Earth’s mantle,” said Nyblade. "The mantle is viscous and over time it flows. If you put a load on it, it slowly flows away and when you remove that load the rock slowly flows back. The viscosity controls how fast that happens. So if it’s gooey enough, as the ice melts there will be quicker rebound. But if it has a higher viscosity and is more stiff, as the ice melts it will take a lot longer to rebound.”

The team used GPS measurements of bedrock uplift from the POLENET network to estimate the viscosity of the mantle and found a much lower viscosity than the global average, explaining the rapid uplift.  The team also obtained seismic images of the mantle that support the low viscosity estimates.

The POLENET network is a National Science Foundation-funded network of GPS and seismic stations installed on bedrock outcrops in West Antarctica to measure the response of the thinning ice. Nyblade and other Penn State researchers have helped run the stations and collect data since 2007. Other partners include Ohio State University, Colorado State, the University of Memphis, the University of Texas, and Washington University in St. Louis.

“We have been using the POLENET data to image the seismic structure of the mantle and what we are finding seismically is consistent with the viscosity structure needed to explain this uplift,” said Nyblade. “What we see seismically is a mantle that has been thermally perturbed, which would create the lower viscosity. It’s hotter than normal, which would reduce the viscosity. If you heat up rock — similar to heating honey — it becomes less viscous. In order to get this rapid uplift, you need to have this low viscosity mantle and we see that seismically. It corroborates the GPS data.”

Although the rapid uplift could potentially slow the melting of the WAIS, scientists are cautious to make definitive predictions.

“We are also finding quite a bit of variability in the mantle structure so we need to look at this effect everywhere in more detail to really understand how it could affect ice sheet dynamics in the future — not in just this one area but across all of West Antarctica," said Nyblade.

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Last Updated July 02, 2018