An abrupt change in texture was relayed in a seawater-filled crevasse at the base of Antarctica’s biggest ice shelf by cameras on the remotely operated Icefin underwater vehicle.
The walls of smooth and cloudy meteoric ice suddenly became green and harder in texture, thereby shifting to salty marine ice.
Almost 1,900 ft above, next to where the surface of the Ross Ice Shelf meets the Kamb Ice Stream, a U.S.-New Zealand research group identified the shift as proof of so-called “ice pumping”—a process never before instantly noted in an ice shelf crevasse, essential to its stability.
We were looking at ice that had just melted less than 100 feet below, flowed up into the crevasse and then refrozen. And then it just got weirder as we went higher up.
Justin Lawrence, Visiting Scholar, Center for Astrophysics and Planetary Science, College of Arts and Sciences, Cornell University
The Icefin robot’s unparalleled look inside a crevasse, and observations disclosing over a century of geological processes below the ice shelf, are elaborated in “Crevasse Refreezing and Signatures of Retreat Observed at Kamb Ice Stream Grounding Zone,” reported March 2nd, 2023, in the Nature Geoscience journal.
The study reports outcomes from a 2019 field campaign to the Kamb Ice Stream assisted by Antarctica New Zealand and other New Zealand research agencies, headed by Christina Hulbe, professor at the University of Otago, and collaborators.
With assistance from NASA’s Astrobiology Program, a research group headed by Britney Schmidt, associate professor of astronomy and earth and atmospheric sciences in A&S and Cornell Engineering, was capable of joining the undertaking and deploying Icefin. Schmidt’s Planetary Habitability and Technology Laboratory has been developing Icefin for almost a decade, starting at the Georgia Institute of Technology.
Integrated with recently reported investigations of the fast-changing Thwaites Glacier–explored the similar cause by a second Icefin vehicle–the research is anticipated to enhance models of sea-level increase by offering the first high-resolution views of ocean, ice, and seafloor interactions at contrasting glacier systems present on the West Antarctic Ice Sheet.
Thwaites, which has been exposed to warm ocean currents, is known to be one of the most unstable glaciers on the continent. Since the late 1800s, Kamb Ice Stream, where the ocean tends to be very cold, has been motionless. At present, Kamb offsets a few of the ice loss from western Antarctica, but if it reactivates, it could increase the contribution of the region to sea-level increase by 12%.
Antarctica is a complex system and it’s important to understand both ends of the spectrum – systems already undergoing rapid change as well as those quieter systems where future change poses a risk. Observing Kamb and Thwaites together helps us learn more.
Britney Schmidt, Associate Professor of Astronomy and Earth and Atmospheric Sciences in A&S and Cornell Engineering, Cornell University
NASA financially supported Icefin’s development and the Kamb exploration to expand ocean exploration beyond Earth. Marine ice like that discovered in the crevasse might be an analog for conditions on the icy moon Europa off of Jupiter, the target of NASA’s Europa Clipper orbital mission slated for launch in 2024. Later lander missions may one day search instantly for microbial life in the ice.
Icefin carries a complete complement of oceanographic instruments on a modular frame over a length of 12 ft and less than 10 inches in diameter. It was lowered on a tether via a borehole that was drilled by the New Zealand team via the ice shelf with hot water.
At the time of three dives covering over three miles next to the grounding zone where Kamb transitions to the floating Ross shelf, Icefin mapped around five crevasses and the sea floor while recording water conditions such as pressure, temperature, and salinity.
Different ice features were noted by the research group that offers useful information regarding melt rates and water mixing. They included ripples, golf ball-like dimples, vertical runnels, and the “weirder” formations next to the top of the crevasse: globs of ice and finger-like protrusions similar to brinicles.
According to the scientists, ice pumping noted in the crevasse possibly adds up to the comparative stability of the Ross Ice Shelf—the world’s largest by area, the size of France–in comparison to Thwaites Glacier.
It’s a way these big ice shelves can protect and heal themselves. A lot of the melting that happens deep near the grounding line, that water then refreezes and accretes onto the bottom of the ice as marine ice.
Peter Washam, Study Second Author and Polar Oceanographer on the Icefin Science Team, Cornell University
On the sea floor, parallel sets of ridges were mapped by Icefin, which the scientists believe are impressions that are left behind by ice shelf crevasses—and a record of 150 years of activity as the Kamb stream stagnated.
Since its grounding line retreated, the ice shelf thinned, resulting in the crevasses lifting away. The slow movement of the ice over time transformed the crevasses seaward of the ridges.
“We can look at those seafloor features and directly connect them to what we saw on the ice base. We can, in a way, rewind the process,” stated Lawrence, the paper’s lead author, now a program manager and planetary scientist at Honeybee Robotics.
Besides Lawrence, Washam, and Schmidt, Cornell co-authors of the study are Senior Research Engineers Matthew Meister, who headed the Icefin engineering team, and Andrew Mullen; Research Engineer Daniel Dichek; and Program Manager Enrica Quartini. Also, Schmidt’s group includes Research Engineer Frances Bryson ’17, and at Georgia Tech, doctoral students Benjamin Hurwitz and Anthony Spears.
Also contributing were collaborators from New Zealand at the National Institute of Water and Atmospheric Research (NIWA); University of Auckland; University of Otago; and Victoria University of Wellington.
Financial guidance was given by NASA for the study through the Planetary Science and Technology from Analog Research program’s Project RISE UP (Ross Ice Shelf and Europa Underwater Probe), and the Future Investigators in NASA Earth and Space Science and Technology program. Extra assistance came from New Zealand’s Antarctic Science Platform, the U.S. Antarctic Program, and Victoria University of Wellington’s Hot Water Drilling initiative.
Lawrence, J. D., et al. (2023) Crevasse refreezing and signatures of retreat observed at Kamb Ice Stream grounding zone. Nature Geoscience. doi.org/10.1038/s41561-023-01129-y