Now we can add underwater “storms” to the troubles around the frozen continent. A new paper shows that eddies at the bottom of an extension of the West Antarctic Ice Sheet, known as the Ice Shelf, are drawing relatively warm water that floats over the Southern Ocean, potentially accelerating its destruction.
The seemingly calm water around the shelf is actually quite chaotic. For one thing, strong winds tear the surface of the sea and push it towards itself. But the ice behind these storms has pros and cons: When it freezes, it releases salt, and when it melts, it flushes fresh H2O into the ocean. This changes the density of the ocean water, creating eddies that draw heat from the depths. “They look exactly like a hurricane,” said lead author Mattia Poinelli, a glaciologist at the University of California, Irvine, and an associate at NASA Jet Propulsion Laboratory, describing the work in the journal Nature Geoscience. “They are highly energetic, so there is a very vertical and turbulent motion near the surface.”
This is bad news for the shelf because it displaces the insulating layer of cold water where the ice meets the ocean, which should prevent melting. Other scientists have found that instead of the underbelly being flat – which would help that insulation layer accumulate – it may be wavy, creating currents that expose the ice to warm water. (Researchers are only recently learning these things because it’s extremely difficult to see what’s happening down there—advanced robots are at work now.) “What we’re really trying to understand is where is the warm water coming from, how is it coming, and what are these processes by which the ice is melting from below?” said Claire Years, a climate scientist at the Korea Polar Research Institute, who was not involved in the new paper.
The troubles beneath the shelf are bad news for the rest of the West Antarctic Ice Sheet. Think of a floating piece like a cork blocking a land-based glacier. If melting along the bottom of the shelf breaks it, the sheet will move into the ocean more rapidly, causing sea levels to rise around the world.
The dramatic decline of sea ice around the continent isn’t helping matters. All those pieces generally act as a buffer, absorbing wave energy that would otherwise crash into the shelf and blow it apart. Sea ice also helps keep ocean temperatures cool: because it is white, it reflects the sun’s energy back into space, but because of its exposure to deeper water, the ocean absorbs that heat.
As sea ice disappears and the shelf degrades, more fresh water is added to the ocean, which means more storms that cause more melting – and this continues unabated. “In the future, where there is more warming water, more melting, we will likely see more of these effects in different areas of Antarctica,” Poinelli said.
These storms may also help explain the retreat of Antarctica’s “grounding lines,” where ice rises above the ground and begins to float on the ocean. Researchers have previously found that as fresh water flows beneath the ice sheet and into the ocean, it creates turbulence that draws warm water in, further accelerating the melting. Earlier this month, a separate team of researchers used a quarter-century of data to find grounding line retreat of up to 2,300 feet per year. When this happens, warm ocean water can reach more parts of the glacier, eating away the ice and making the entire sheet system less stable.
And now storms can increase this attack on the grounding line. “This study provides a compelling mechanism for the small but powerful storms that punch holes beneath the ice and accelerate melting,” said University of Houston physicist Pietro Milillo, who co-authored the retreat paper but was not involved in the storm research. “The kind of return we see in our dataset can be partly explained by these underwater storms.”
How much more melting we may see due to these storms remains an open question. Additionally, the finding comes from a model, although Poinelli said scientists have observed the dynamics in another region of Antarctica. Scientists desperately need more data to get a better idea of how quickly this ice will disappear and, as a result, how fast sea levels will rise. “We sometimes think that the ice sheet responds slowly to changes, but this work and ours remind us that Antarctica can change on time scales of days or weeks,” Mililo said. “We need to monitor the bottom of the ice shelf with the same urgency we monitor atmospheric storms.”
This article originally appeared in Grist at https://grist.org/science/violent-storms-hidden-under-antarcticas-ice-could-be-speeding-its-decline/. Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and an equitable future. Learn more at Grist.org.
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