Crevasses, which are more than just cracks in the ice, play a significant role in circulating seawater beneath Antarctic ice shelves, potentially influencing their stability, according to Cornell University-led research based on a first-of-its-kind underwater robot exploration.
The trek up and down a crevasse at the base of the Ross Ice Shelf by the remotely controlled Icefin robot gave the first 3D observations of ocean conditions near where it meets the coastline, a key junction known as the grounding zone.
In addition to rising and sinking currents and different ice structures formed by varying flows and temperatures, the robotic study showed a unique circulation pattern—a jet funneling water sideways down the chasm. These insights will help predict ice shelf melting and freezing rates at grounding zones, where there are limited direct observations, as well as their potential contribution to global sea-level rise.
“Crevasses move water along the coastline of an ice shelf to an extent previously unknown, and in a way that models did not predict,” said Peter Washam, a polar oceanographer and Cornell University research scientist. “The ocean takes advantage of these features, and you can ventilate the ice shelf cavity through them.”
Washam is the first author of the paper “Direct Observations of Melting, Freezing, and Ocean Circulation in an Ice Shelf Basal Crevasse,” which was published in Science Advances.
The Icefin vehicle—roughly 12 feet long and less than 10 inches around—was released in late 2019 on a tether down a 1,900-foot borehole drilled with hot water, close to where Antarctica’s greatest ice shelf meets the Kamb Ice Stream. Grounding zones are critical for managing the balance of ice sheets and are the locations where altering ocean conditions can have the greatest impact.
Matthew Meister, a senior research engineer, drove Icefin into one of five crevasses identified near the borehole during the team’s final of three dives. The vehicle, which was outfitted with thrusters, cameras, sonar, and sensors for detecting water temperature, pressure, and salinity, climbed roughly 150 feet up one slope and descended the other.
As the fissure closed, the ice patterns changed, with scalloped indentations giving place to vertical runnels, then green-tinted marine ice and stalactites. Melting at the crevasse base and salt rejection from freezing near the top caused water to travel up and down across the horizontal jet, causing unequal melting and freezing on both sides, with more melting along the lower downstream wall.
“Each feature reveals a different type of circulation or relationship of the ocean temperature to freezing,” Washam told the audience. “Seeing so many different features within a crevasse, so many changes in the circulation, was surprising.”
The findings, according to the researchers, show crevasses’ ability to carry changing ocean conditions—warmer or colder—through an ice shelf’s most vulnerable section.
“If the water heats up or cools off, it can move around in the back of the ice shelf quite vigorously, and crevasses are one of the means by which that happens,” Washam said in a statement. “When it comes to projecting sea-level rise, that’s important to have in the models.”
