Based on a first-of-its-kind underwater robotic study, Cornell University-led research has found that cracks, rather than cracks in the ice, play a significant role in the circulation of seawater beneath Antarctic ice shelves, potentially affecting their stability.

The remote-controlled Icefin robot climbed up and down the strait at the foot of the Ross Ice Shelf, making the first three-dimensional measurements of ocean conditions near where it meets the coastline at a critical point known as the landfall zone.

The robotic study revealed a new circulation pattern—jets that send water sideways across the crack—in addition to updrafts and downdrafts, as well as various ice formations created by changing flows and temperatures. These details will improve modeling of ice shelf melting and freezing rates in landlocked areas where direct observations are scarce and their potential contribution to global sea level rise.

“The rifts move water along the coastline of the ice shelf at rates previously unknown and not predicted by models,” said Peter Washam, a polar oceanographer and research scientist at Cornell University. “The ocean takes advantage of these opportunities, and with their help you can ventilate the space of the ice shelf.”

Washam is the lead author of “Direct Observations of Melting, Freezing, and Ocean Circulation in the Basal Rift of an Ice Shelf,” published in the journal Science Advances.

In late 2019, scientists launched Icefin, which is about 12 feet long and less than 10 inches in diameter, via a cable into a 1,900-foot-long borehole drilled with hot water near where Antarctica’s largest ice shelf meets the ice flow. These so-called grounding zones are key to controlling the stability of ice sheets and are where changing ocean conditions can have the greatest impact.

On the last of the team’s three dives, senior research engineer Matthew Meister drove Icefin into one of five fissures discovered near the well. Equipped with engines, cameras, sonar and sensors to measure water temperature, pressure and salinity, the vehicle climbed approximately 150 meters up one slope and down another.

The study detailed the change in ice structure as the crack narrowed: jagged depressions gave way to vertical currents, then green-tinted sea ice and stalactites. Melting at the base of the crack and refusal of salt to freeze near the top moved water up and down around the horizontal jet, causing uneven melting and freezing on both sides, with more intense melting occurring along the downstream lower wall.

“Each feature shows a different type of circulation or relationship between ocean temperature and freezing,” Washam said. Said. “It was surprising to see so many different features inside the crack, so many changes in circulation.”

The findings highlight the potential for cracks to transmit changing ocean conditions (warmer or colder) across the ice shelf’s most vulnerable region, the researchers said.

“If water warms or cools, it can move quite strongly behind the glacier, and crevasses are one of the ways that this happens,” Washam said. “When it comes to predicting sea level rise, it’s important to include this in models.”