Even as parts of West Antarctica are melting rapidly, the sea level is rising, and large ice packs remain stable for the time being. Scientists have already explored one of those stable places – the lonely corner where the ocean meets the ice. There, the team found strange shapes, circles, and balls carved under the ice.
This environment is “really on the edge” between melting and freezing, says planetary scientist Justin Lawrence. The delicate balance between these two processes is molding the ice into those strange textures—the same way that minerals dissolve and recrystallize into beautiful shapes inside limestone caves.
The result, at the Kamb Ice Stream, is that large cracks beneath the ice appear to have frozen together as ball-sized balls filled in the caves above, Lawrence and colleagues report on March 2. Nature Geoscience.
This cooling is different from what happens at Thwaites Glacier in Antarctica. There, scientists recently reported these cracks, known as basal crevasses, as areas of rapid melting (SN: 2/15/23).
Understanding what is happening at Kamb will help scientists predict how much of the Antarctic coast that is not currently vulnerable will respond as the world continues to warm due to human-induced climate change. Here is something else about Kamb.
The super-cold water is under the ice in Kamb, the burning sonipes
In December 2019, two teams of researchers from New Zealand and the United States visited the Kamb Ice Stream – a type of ice that consists of a channel of faster moving ice surrounded by slower ice.
Kamb, like much of the rest of the West Antarctic Ice Sheet, lies on a bed that is hundreds of meters below sea level. The New Zealand ridges used warm water to break a narrow opening through the ice, just downstream of the “founder zone” where the glacier raises its muddy bed and floats in the ocean.
The US team then lowered the remotely operated vehicle that Icefin descended through 580 meters of ice and into the lower seawater. The Icefin researchers piloted it up to a kilometer from the borehole, navigating by video transmitted through the borehole. At the time of the campaign, the Icefin team was affiliated with Georgia Tech in Atlanta, but has since moved to Cornell University, except for Lawrence. He now works for Honeybee Robotics, a private company in Altadena, Calif.
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Icefin found that much of the seawater under Kamb is about 0.3 degrees Celsius above freezing. But directly below the ice sits a colder layer, a mixture of seawater and glacial meltwater only 0.02 to 0.08 degrees C above freezing. Based on these measurements, Lawrence and his colleagues estimate that under the exposed Kamb melts about 26 centimeters per year.
By contrast, recent measurements at the increasingly unstable Thwaites Glacier, about 1,400 kilometers to the northeast, found seawater at the ice zone 1 to 2 degrees C warmer than at Kamb — and the ice melting at 5 to 40 meters per year.
The new discovery at Kamb makes sense, says New Zealand member Christina Hulbe of the University of Otago, because the seabed at Kamb is relatively shallow. So it is not subject to the deep, warm ocean tides that hit the Thwaites.
Much of Antarctica is fringed by a cold ocean environment, Kamb says. “So we have to understand that the system is very important.”
Balls that freeze ice cracks to fill Kamb
When Icefin crept in, its sonar mass detected basal crevasses up to 55 meters above the ice. These cracks probably formed as a floating piece of ice, an ice shelf, was bent up and down by ocean tides.
Lawrence and his colleagues guided an ROV into one of these cracks, and found its white, icy sides carved into a narrow vertical cleft. The icefin ascended 40 meters until the crevasses suddenly disappeared — replaced by a jumble of ice balls that seemed to fill the upper part of the crevasse.
The globules were pale — the color of winter ice that forms on the surface of the ocean often seen. This color, Lawrence and his colleagues think, forms from an ultra-cold mixture of seawater and meltwater that is transported into the crack and cools, gradually filling the crack, from top to bottom, over many decades. They think that this should be observed in all the vents. These, he says, heal cavities effectively.
Lawrence speculates that this cooling process may also explain the amazing vertical alignment in the crevasse walls. As the water freezes, the salt is released from the newly formed crystals, creating small pockets of condensation. That wall of thick mud flows down, the cracks melting into ice – in the same way that salt melts ice when it is sprinkled on a winter star.
To observe the crevasses cooling under Kamb “is pretty amazing,” says Ginny Catania, a glaciologist at the University of Texas at Austin who was not part of the project. Those cracks “can push up to the surface and warm” the glaciers, he says, which can horrify the ice shelf if it happens too quickly, shrinking the ice and raising sea levels.
And if the vents can also heal, these crusts are more resistant to childbirth, and can make it more stable than scientists have realized, at least as long as the ice inside continues to be washed with cold water.
A string of instruments installed in the pit continued to measure the temperature and salinity of the water beneath the ice—by transmitting a cable to the surface of the ice and sending it back home via satellite until the batteries ran out two years later. Those data show conditions down below remaining cool and comfortable for Kamb.
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