High in a narrow seawater-filled crevasse at the base of Antarctica’s largest ice shelf, cameras from the Icefin remotely operated underwater vehicle relayed a sudden change in the landscape.
Walls of smooth, cloudy meteoric ice abruptly turned green and rougher in texture, fading to salty sea ice.
Nearly 1,900 feet above, near where the surface of the Ross Ice Shelf meets Kamb Ice Stream, an American-New Zealand research team recognized the change as evidence of “pumping of ice” – a process never observed directly in an ice shelf crevice, important to its stability.
“We were looking at ice that had just melted less than 100 feet below, flowed into the crevasse and then refreezed,” said Justin Lawrence, visiting scholar at the College of Arts and Sciences (A&S) Cornell Center for Astrophysics and Planetary Science. . “And then it got weirder as we got higher.”
The Icefin robot’s unprecedented look inside a crevasse and observations revealing more than a century of geological processes beneath the pack ice are detailed in “Crevasse refreeze and shrinkage signatures seen in the Kamb Ice Stream grounding area», published on March 2 in Nature Geoscience.
The article reports the results of a 2019 field campaign on Kamb Ice Stream supported by Antarctica New Zealand and other New Zealand research agencies, led by Christina Hulbe, Professor at the University of Otago, and her colleagues. With support from NASA’s Astrobiology Program, a research team led by Britney Schmidt, associate professor of astronomy and earth and atmospheric sciences at A&S and Cornell Engineering, was able to join the expedition and deploy Icefin. Schmidt’s Planetary Habitability and Technology Lab has been developing Icefin for nearly a decade, beginning with the Georgia Institute of Technology.
Members of Britney Schmidt’s Icefin team after completing their first mission to explore conditions under the Ross Ice Shelf in Antarctica, near where it meets the Kamb Ice Stream, in December 2019. – Icefin/NASA PSTAR RISE UP/Schmidt
Combined with recently published investigations of the rapidly changing Thwaites Glacier – explored the same season by a second Icefin vehicle – the research is expected to improve models of sea level rise by providing the first high-resolution views of the ice, ocean and seabed interactions at contrasting ice systems on the West Antarctic Ice Sheet.
Thwaites, which is exposed to warm ocean currents, is one of the continent’s most unstable glaciers. Kamb Ice Stream, where the ocean is very cold, has stagnated since the late 1800s. Kamb is currently offsetting some of the ice loss from West Antarctica, but if it reactivates, it could increase the region’s contribution to sea level rise of 12%.
“Antarctica is a complex system and it’s important to understand both ends of the spectrum – systems that are already undergoing rapid change as well as quieter systems where future change poses a risk,” Schmidt said. “Watching Kamb and Thwaites together helps us learn more.”
NASA funded Icefin development and Kamb exploration to expand ocean exploration beyond Earth. Sea ice like that found in the crevasse may be an analogue of conditions on Jupiter’s icy moon Europa, the target of NASA’s Europa Clipper orbital mission slated for launch in 2024. Subsequent lander missions could un directly look for microbial life in the ice.
Icefin carries a full range of oceanographic instruments on a modular chassis over 12 feet long and less than 10 inches in diameter. He was lowered on a tether through a borehole which the New Zealand team drilled through the pack ice with hot water.
During three dives spanning more than three miles near the grounding area where Kamb passes the Ross Floating Shelf, Icefin mapped five crevasses – one ascending – and the seabed, while recording sea conditions. water, including temperature, pressure and salinity.
The team observed various features of the ice that provide valuable information about water mixing and melt rates. They included golf ball-shaped dimples, ripples, vertical rills, and the “strange” formations near the top of the crevasse: balls of ice and finger-like protrusions resembling brinicles.
Remote controlled Icefin Credit: Icefin/NASA PSTAR RISE UP/Schmidt/Lawrence
The Icefin remote-controlled underwater robot after diving under the Ross Ice Shelf near Kamb Ice Stream in 2019.
The ice pumping observed in the crevasse likely contributes to the relative stability of the Ross Ice Shelf – the world’s largest by area, the size of France – compared to Thwaites Glacier, the researchers said. .
“It’s a way for these large ice shelves to protect and heal themselves,” said Peter Washam (A&S), polar oceanographer with the Icefin science team and second author of the paper. “Much of the melting that occurs at depth near the grounding line, this water then freezes and collects on the ice floor as sea ice.”
On the sea floor, Icefin has mapped parallel sets of ridges that the researchers say are imprints left by crevasses in the pack ice – and a record 150 years of activity since Kamb Creek stagnated. As its grounding line receded, the pack ice thinned, causing the crevasses to uplift. The slow movement of the ice over time moved the crevasses seaward of the ridges.
“We can look at these seabed features and relate them directly to what we’ve seen on the ice base,” said Lawrence, the paper’s lead author, now a program manager and planetary scientist at Honeybee Robotics. “We can kind of rewind the process.”
The bottom heat pipe contour in the crevasse water column (Supplemental Video 4 Extended Data Fig. 5) is interpolated from white sample points (vehicle track), with a contour line of 0° C delimiting the supercooling horizon. Insets a through i illustrate the different ice textures and morphologies in the order of encounter (full images in Extended Data Fig. 5); c and g show the appearance of sea ice along opposite sides of the crevasse at about the same height. The vehicle path is misaligned by approximately 5-10 m from the ice profile due to southward movement along the longitudinal axis of the crevasse (in the page) and accumulated positioning error of the vehicle ; however, all data (and the length of the Icefin ROV) are to scale; 2× horizontal exaggeration. — Natural Geoscience
In addition to Lawrence, Washam and Schmidt, co-authors of the Cornell research are senior research engineers Matthew Meister, who led Icefin’s engineering team, and Andrew Mullen; Research engineer Daniel Dichek; and program manager Enrica Quartini. Schmidt’s team also includes research engineer Frances Bryson ’17 and, at Georgia Tech, doctoral students Benjamin Hurwitz and Anthony Spears.
New Zealand partners from the National Institute for Water and Atmospheric Research (NIWA) also contributed; University of Auckland; University of Otago; and Victoria University of Wellington.
NASA supported the research through the RISE UP project of the Planetary Science and Technology from Analog Research (Ross Ice Shelf and Europa Underwater Probe) program and the Future Investigators in NASA Earth and Space Science and Technology program. Additional support came from New Zealand’s Antarctic Science Platform, the US Antarctic Program and the Victoria University of Wellington’s Hot Water Drilling Initiative.
Crevasse refreeze and retreat signatures observed in the Kamb Ice Stream grounding area, Nature Geoscience (open access)
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