If you’ve ever built a sandcastle on the beach, you’ve seen how seawater in the sand can quickly undermine the castle. A new study by the British Antarctic Survey has concluded that warmer seawater may act in a similar way on the undersides of Earth’s ice sheets, melting them faster than previously thought.
That means computer models used to predict ice sheet melting activity in Antarctica may be underestimating the extent to which warming water beneath the ice is contributing to the melting, concludes a study published Tuesday in the journal Nature Geoscience.
Faster melting of the ice sheets could bring more flooding earlier than expected to coastal communities along the U.S. East Coast, which are already seeing more days with high tides and flooding along the coast and coastal rivers.
The study is at least the second in five weeks to report that warmer ocean water may be helping ice melt in glaciers and ice sheets faster than previously modeled. Scientists are working to improve these crucial models used in sea level rise planning.
Relatively warmer ocean water can penetrate long distances beyond a boundary known as the “grounding zone,” where land ice meets the sea and floating ice shelves, seeping between the land below and the ice sheet, a new study says. And that could have “dramatic consequences” in contributing to sea level rise.
“We identified the possibility of a new tipping point in the melting of the Antarctic ice sheet,” said lead study author Alex Bradley, an ice dynamics researcher on the survey. “This means that our sea-level rise projections may be significantly underestimated.”
“Ice sheets are very sensitive to melting in their grounding zone,” Bradley said. “We found that melting in the grounding zone behaves like a ‘tipping point,’ where a very small change in ocean temperature can cause a very large increase in the grounding zone, which would lead to a very large change in the ice flow above it.”
The study follows an unrelated study published in May that found “vigorous melting” on Antarctica’s Thwaites Glacier, commonly referred to as the “doomsday glacier”. This study, published in the journal Proceedings of the National Academy of Sciences, provided visible evidence that warm seawater is pumping under the glacier.
Land glaciers in Antarctica and Greenland are gradually sliding towards the ocean, forming a boundary at the edge of the sea where melting can occur. Scientists report that melting along these zones is a major factor in rising sea levels worldwide.
Water seeping under the ice sheet opens up new cavities, and these cavities allow more water in, which in turn melts even larger chunks of ice, the British Antarctic Survey concluded. Small increases in water temperature can speed up this process, but computer models used by the Intergovernmental Panel on Climate Change and others do not account for this, the authors found.
“This is missing physics that is not in our ice sheet models. They don’t have the ability to simulate melting under grounded ice, which is what we think is happening,” Bradley said. “Now we’re working to incorporate that into our models.”
Lead author of the previous study, published in May, Eric Rignot, a glaciologist at the University of California, Irvine, told USA TODAY that much more seawater flows into the glacier than previously thought, making the glacier “more sensitive to ocean warming.” and more likely to break up as the ocean warms.”
On Tuesday, Rignot said the survey research provides “further incentives to study this part of the glacial system in more detail,” including the importance of tides, which make the problem more severe.
“These and other studies pointing to greater sensitivity of the glacier to warm water mean that sea level rise in the coming century will be much greater than expected, and perhaps twice as much,” Rignot said.
Contributor: Doyle Rice, USA TODAY