Underwater robot gives insight into ice shelf crevasses

A research team led by Cornell University is using an underwater robot, called Icefin, to gain a better understanding of ice shelf crevasses. 

Crevasses in ice play an important role in helping to circulate seawater beneath Antarctic ice shelves. This circulation can potentially influence the stability of the shelves, according to the research team. In particular, the team studied the Ross Ice Shelf, the largest ice shelf in Antarctica. 

Icefin is a tube-shaped robot roughly 12 feet long and less than 10 inches around. It is equipped with thrusters, cameras, sonar, and sensors for measuring water temperature, pressure, and salinity. First deployed in 2019, the robot can climb up and down crevasses in the base of ice shelves.

The robot revealed a new circulation pattern, a jet funneling water sideways through the crevasse it was studying, in addition to rising and sinking currents, and diverse ice formations shaped by shifting flows and temperatures. 

For its work in the Ross Ice Shelf, Icefin was deployed on a tether down a 1,900-foot borehole drilled with hot water, near where the ice shelf meets the Kamb Ice Stream. This was an ideal place for the team to study the long-term effects of underwater conditions, as the Ross Shelf is older than previously explored ice shelves, making it more representative of Antartcia’s other ice shelves, and the Kamb Ice Stream is stagnant.

This climb resulted in the first 3D measurements of ocean conditions near where it meets the coastline, an important juncture known as the grounding zone. These grounding zones are key to controlling the balance of ice sheets, and the places where changing ocean conditions have the most impact. 

On the last of three dives, Matthew Meister, a senior research engineer, drove Icefin into one of five crevasses near the team’s borehole. The robot climbed almost 150 feet up one slope and descended the other. 

With the robot, the team was able to detail changing ice patterns as the crevasse narrowed. They found that melting at the crevasse base and salt rejection from freezing near the top moved water up and down around the horizontal jet steam, driving uneven melting and freezing on the two 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,” Peter Washam, a polar oceanographer and research scientist in the Department of Astronomy at Cornell and lead author on the paper, said. “Seeing so many different features within a crevasse, so many changes in the circulation, was surprising.”

The research team believes it’s likely that similar conditions exist in adjacent crevasses. The findings highlight crevasses’ potential to transport changing ocean conditions through an ice shelf’s most vulnerable region. 

“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. “When it comes to projecting sea-level rise, that’s important to have in the models.”

These new discoveries will help to improve the modeling of ice shelf melting and freezing rates at grounding zones and of their potential contribution to global sea-level rise. 

The Icefin team was led by Britney Schmidt, an associate professor of astronomy and earth and atmospheric sciences and Cornell Engineering, and the director of the Planetary Habitability and Technology Lab. The research also included members of a New Zealand-based research team led by Christina Hulbe, a professor at the University of Otago. 

This research was funded by Project RISE UP (Ross Ice Shelf and Europa Underwater Probe), part of NASA’s Planetary Science and Technology from Analog Research program, with logistical support provided by the National Science Foundation through the U.S. Antarctic Program.