Jun 21, 2018

Rising ground under West Antarctica could prevent ice sheet collapse

A section of the West Antarctic Ice Sheet with mountains is viewed from a window of a NASA Operation IceBridge airplane on October 31, 2016 in-flight over Antarctica. Credit: Mario Tama/Getty Images.

A new study finds that the ground underneath the West Antarctic Ice Sheet region is rebounding, or rising, at an extraordinarily rapid rate.

Why this matters: Previous research has shown that enough ice has already melted in this region to trigger a potentially irreversible melt of the West Antarctic Ice Sheet, which would sharply increase sea levels worldwide. Now, though, scientists may have identified a new brake on this runaway train.

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As the ice melts, there is less weight being placed on the bedrock below. This is causing the ground level to rise through a process known as glacial isostatic adjustment, or rebound. (Such a process is still underway in parts of North America from the end of the last ice age.)

If the underlying bedrock rises fast enough, it could halt the loss of ice from this region, the study, out today in the journal Science, finds.

  • New measurements found that the ground under the rapidly melting Amundsen Sea Embayment of West Antarctica is rising at the astonishingly rapid rate of 41 millimeters, or more than 4 cm, per year.
  • If this trend increases as the study projects, then the grounding line, which is the spot where the marine-based ice shelf of the Pine Island Glacier meets bedrock, will have risen by 8 meters, or 26.2 feet, in 100 years, according to an Ohio State University press release.
  • The study utilized ground-based GPS sensors as well as satellites that measure subtle changes in gravitational fields.

Terry Wilson, a co-author of the study and professor emeritus at Ohio State, told Axios that the rebound rate measured at the West Antarctic Ice Sheet is the fastest ever measured at any ice sheet on the planet.

What this means: The rapid uplift rate — determined using ground-based GPS instruments — means that there's a greater chance that certain so-called "pinning points" underneath the ice that could catch hold of a moving ice floe and keep it in place. The authors of the study say the rapid response of the Earth's surface to the ice melt indicates the ground deep underneath that part of Antarctica is hotter and more fluid (or less viscous) than presumed, and therefore has a more rapid response rate.

Wilson says that if greenhouse gas emissions continue unabated, the rising ground level underneath West Antarctica won't be sufficient to stop it from melting. However, under moderate emissions scenarios, it would, based on early computer model simulations.

What they're saying: Researchers who were not involved in the new study are treating it with cautious optimism, saying more research is needed before concluding this is truly good news.

"The ice-flow community will use these, and other, new data to make better projections.  I believe that as these new model experiments are conducted, the data from this new paper will prove to be important but not dominant, and that human decisions about our energy system are still the most important influence on future sea-level rise.  But, in coming years, the estimates of sea level rise will be more accurate because of this work." 
— Richard Alley, a geoscientist at Penn State University.

Robert DeConto, an ice sheet researcher at the University of Massachusetts, whose work has pointed to the dangers of losing the West Antarctic Ice Sheet, says he doesn't see the new results as a game-changer — at least not yet.

"I remain optimistic, but currently, Antarctica’s greatest contribution to sea level rise is coming from the very region in Antarctica where this process should be helping slow things down," he said. "... I’m not sure our low lying coastlines can wait for the Earth’s soft interior to save the day, no matter how viscous it might be."

And Natalya Gomez of McGill University, who is working to incorporate the rising bedrock into computer models of how ice sheets will respond to global warming, told Axios that the new study reinforces the consensus view that our decisions in the next few decades will prove pivotal to the fate of Antarctic ice.

"In my view, with insight from the modeling I have done, this feedback will play a more important role in slowing or stopping ice sheet retreat in this region in a low-end warming scenario, but less so in a high-end scenario — with enough warming in Antarctica, this region will retreat and lead to substantial sea level rise.”
— Natalya Gomez, McGill University

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