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 concludes that warmer seawater may act in a similar way on the lower part of land ice sheets, melting them faster than previously thought.
That means computer models used to predict the melting activity of the Antarctic ice sheet may be underestimating how much the long range of warming water beneath the ice is contributing to the melting, concluded the study, published Tuesday in the journal Nature Geoscience.
Faster melting of the ice sheet could lead to more flooding earlier than expected for coastal communities along the US East Coast, where they are already seeing more days of high tides and flooding along coasts and coastal rivers.
The study is at least the second in five weeks to report that warmer ocean water may be helping to melt ice in glaciers and ice sheets faster than previously modeled. Scientists are working to improve these key models, which are used to help plan for sea-level rise.
Relatively warmer ocean water can penetrate long distances beyond the 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, the new study reports. And it could have “dramatic consequences” by contributing to sea level rise.
“We identified the possibility of a new tipping point in the melting of the Antarctic ice sheet,” said lead author Alex Bradley, an ice dynamics researcher on the study. “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 find that grounding zone melting exhibits tipping-point-like behavior where a very small change in ocean temperature can cause a very large increase in grounding zone melting, which would lead to a very large change in ice flow over her.”
The research follows an unrelated study published in May that found “vigorous melting” of Antarctica’s Thwaites Glacier, commonly referred to as the “Doomsday Glacier”. This study, published in the Proceedings of the National Academy of Sciences, reports visible evidence that warm seawater is being pumped beneath the glacier.
The land-based ice sheets in Antarctica and Greenland are gradually sliding toward the ocean, forming a margin at the edge of the sea where melting can occur. Scientists report that melting in these areas is a major factor in sea level rise around the world.
Water entering under the ice sheet opens new cavities and these cavities let in more water, which in turn melts even larger areas of ice, the British Antarctic Survey concluded. Small increases in water temperature can accelerate 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 the melting under ground ice that we think is happening,” Bradley said. “Now we’re working on bringing that into our models.”
The 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 is flowing into the glacier than previously thought, making the glacier “more sensitive to warming of the ocean and is more likely to break down as the ocean gets warmer.”
On Tuesday, Rigneault said the survey’s research provides “further incentives to study this part of the glacial system in more detail,” including the importance of tides that make the problem more important.
“These and other studies pointing to greater sensitivity of the glacier to warm water mean that sea-level rise over the next century will be much greater than expected, and possibly as much as twice as much,” Rigneault said.
Contributing: Doyle Rice, USA TODAY
