The West Antarctic Ice Sheet covers an area of about 760,000 square miles and is up to 1.2 miles thick. If it ever completely melted, it would increase global sea levels by 10 feet. Even given how quickly humans are warming the planet, such changes would likely take centuries to occur—that's how much ice we're talking about here. But scientists are finding more and more evidence that Antarctica's ice is in much greater danger than previously thoughtwith many drastic changes such as sea ice lossstrengthening each other.
Underwater “storms” can now be added to the troubles unfolding around the frozen continent. new paper suggests the eddies are pulling relatively warm water across the lower part of the West Antarctic ice sheet, known as an ice shelf, floating in the Southern Ocean, potentially accelerating its destruction.
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The seemingly calm waters around the shelf are actually quite chaotic. Firstly, strong winds blow across the sea surface, pushing it forward. But what causes these storms is the gain and loss of ice: when it freezes, it releases salt, and when it melts, it releases fresh H2O into the sea. This changes the density of ocean water, creating vortices that draw heat from the depths. “They look exactly like a storm,” said lead author Mattia Poinelli, a glaciologist at the University of California, Irvine and a postdoctoral fellow at NASA's Jet Propulsion Laboratory, describing the work in the journal Nature Geoscience. “They are very energetic, so there is very vertical and turbulent motion near the surface.”
This is bad news for the shelf because it displaces an insulating layer of cold water where the ice meets the sea, which should prevent melting. Other scientists have found that instead of the lower abdomen being flat (which would encourage the accumulation of an insulating layer), it can move in waves, creating currents. which similarly expose ice to warm waters. (Researchers are only recently studying these things because it's extremely difficult to see what's going on there – advanced robots now do their jobs.) “We're really trying to understand where the warm water gets, how does it get there, and what are these processes by which the ice melts from below?” said Claire Ayres, a climate scientist at the Korea Polar Research Institute who was not involved in the new paper.
Problems below the shelf are bad news for the rest of the West Antarctic Ice Sheet. Think of the floating piece as a plug holding a glacier resting on land. If melting at the bottom of the shelf causes it to collapse, the layer will rush into the ocean faster, raising sea levels around the world.
The sharp decline in sea ice surrounding the continent isn't helping matters either. All of these pieces usually act as a buffer, absorbing wave energy that would otherwise crash into the shelf and break it apart. Sea ice also helps keep sea temperatures cool: because it is white, it reflects solar energy back into space, but when darker waters are exposed, the sea absorbs that heat instead.
As sea ice disappears and shelves degrade, more fresh water is added to the ocean, which means more storms, which lead to more melting—and so on and so forth. “In the future, when there is more warm water and 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 breaks away from the land and begins to float in the ocean. Researchers have previously found that when fresh water flows under the ice sheet into the ocean, it creates turbulence that draws in warm water, further accelerating the melting. Earlier this month, a separate group of researchers used data for a quarter of a century detect ground line retreat up to 2,300 feet per year. When this happens, warm ocean water will be able to access more of the glacier, eating away at the ice and making the entire ice cover system less stable.
And now storms can intensify this attack on the grounding line. “This study demonstrates a compelling mechanism for tiny but powerful storms that breach beneath the ice and accelerate melting,” said Pietro Milillo, a physicist at the University of Houston who co-authored the report but was not involved in the storm research. “The retreat we see in our data set can be partially explained by these underwater storms.”
How much more melting we might see from these storms remains an open question. Additionally, the discovery was based on a model, although Poinelli said scientists observed the dynamics in another area of Antarctica. Scientists desperately need more data to get a better idea of how quickly this ice will disappear and, as a result, how quickly sea levels will rise. “Sometimes we think that the ice sheet is slow to respond to change, but this work and our work reminds us that Antarctica can change in a matter of days or weeks,” Milillo said. “We need to monitor the lower part of the ice shelf with the same urgency that we monitor atmospheric storms.”
