by High up in a narrow, seawater-filled fissure at the base of Antarctica’s largest ice shelf, cameras from the Icefin remotely operated underwater vehicle showed a sudden change in the landscape.
Walls of smooth, cloudy meteorite ice suddenly turned green and rougher in texture, merging into salty sea ice.
Nearly 1,900 feet above, near where the surface of the Ross Ice Shelf meets the Kamb Ice Stream, an American-New Zealand research team recognized the shift as evidence of “ice pumping” – a process never before seen directly in an ice shelf fissure was observed. important for its stability.
“We looked at ice that had just melted less than 100 feet below, flowed into the fissure, and then refrozen,” said Justin Lawrence, a visiting scientist at the Cornell Center for Astrophysics and Planetary Science. “And then it just got weirder the higher we got.”
The Icefin robot’s unprecedented view into a crevasse and observations revealing more than a century of geological processes beneath the Ice Shelf are featured in “Crevasse Refreezing and Signatures of Retreat Observed at Kamb Ice Stream Grounding Zone,” published April 2 nature geosciences.
The paper reports the results of a 2019 field campaign on the Kamb Ice Flow, supported by Antarctica New Zealand and other New Zealand research institutions led by University of Otago Professor Christina Hulbe and 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 Cornell University, was able to join the expedition and use Icefin. Schmidt’s Planetary Habitability and Technology Lab has been developing Icefin for nearly a decade, beginning at the Georgia Institute of Technology.
Combined with recently published surveys of the rapidly changing Thwaites Glacier – explored by a second Icefin craft in the same season – the research is expected to improve sea level rise models by providing the first high-resolution views of ice, ocean and Seafloor interactions at contrasting glacial systems on the West Antarctic Ice Sheet.
Subject to warm ocean currents, Thwaites is one of the continent’s most unstable glaciers. The Kamb Ice Flow, where the ocean is very cold, has been stagnant since the late 19th century. Kamb is currently offsetting some of the ice loss from West Antarctica, but if reactivated it could increase the region’s contribution to sea level rise by 12%.
“Antarctica is a complex system, and it’s important to understand both ends of the spectrum — systems that are already changing rapidly, as well as the quieter systems where future changes pose a risk,” Schmidt said. “Kamb and Thwaites’ joint observation helps us learn more.”
NASA funded the development of Icefin and Kamb exploration to extend ocean exploration beyond Earth. Sea ice like that found in the fissure may be an analogue of conditions on Jupiter’s icy moon Europa, the target of NASA’s Europa Clipper orbital mission, scheduled for launch in 2024. Later lander missions could one day directly search for microbial life in the ice.
Icefin carries a full array of oceanographic instruments on a modular frame more than 12 feet long and less than 10 inches in diameter. It was lowered on a tether through a borehole that the New Zealand team had drilled through the ice shelf using hot water.
During three dives spanning more than three miles near the touchdown zone, where Kamb merges with the floating Ross Shelf, Icefin mapped five fissures – one ascending – and the seafloor while recording water conditions such as temperature, pressure and salinity .
The team observed various ice features that provide valuable information about water mixing and melt rates. These included golf ball-like dimples, ripples, vertical gullies, and the “stranger” formations near the top of the fissure: lumps of ice and finger-like protrusions resembling brinicels.
The ice pumping seen in the fissure 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.
“This allows these large ice shelves to protect and heal themselves,” said Peter Washam, polar oceanographer on the Icefin science team and second author of the paper. “Much of the melting that occurs deep near the baseline, that water then refreezes and accumulates as sea ice at the bottom of the ice.”
On the seafloor, Icefin mapped parallel rows of ridges that the researchers believe are imprints left by crevasses of the ice shelf – and a record of 150 years of activity since the Kamb Current stagnated. As its baseline retreated, the ice shelf thinned, causing crevasses to loosen. The slow movement of the ice over time moved the crevasses seaward of the ridges.
“We can look at these seafloor features and connect them directly to what we saw on the ice base,” said Lawrence, the paper’s lead author, now a program manager and planetary scientist at Honeybee Robotics. “We can sort of rewind the process.”
Along with Lawrence, Washam and Schmidt, the Cornell co-authors of the 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 and Georgia Tech graduate students Benjamin Hurwitz and Anthony Spears.
Also involved were partners from New Zealand at the National Institute of Water and Atmospheric Research (NIWA); University of Auckland; University of Otago; and Victoria University of Wellington.
NASA supported the research through the Planetary Science and Technology from Analog Research program’s RISE UP (Ross Ice Shelf and Europa Underwater Probe) project 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 Victoria University of Wellington’s Hot Water Drilling Initiative.
