by High in a narrow, sea-filled rift at the base of Antarctica’s largest ice shelf, cameras on the remotely operated underwater vehicle Icefin broadcast a sudden change in scenery.
The walls of smooth, cloudy meteoric ice suddenly turned green and rougher in texture, transitioning to salty sea ice.
Nearly 1,900 feet up, near where the surface of the Ross Ice Shelf meets the Kamb Ice Stream, a US-New Zealand research team identified the drift as evidence of “ice pumping” — a process never before directly observed in a icebox crack. important for its stability.
“We were looking at ice that had just melted less than 100 feet down, flowed down the fissure, and then refrozen,” said Justin Lawrence, a visiting scholar at Cornell’s Center for Astrophysics and Planetary Science. “And then it got weirder the higher we went.”
The Icefin robot’s unprecedented look inside a crevasse and observations that reveal more than a century of geologic processes beneath the ice shelf are detailed in “Crevasse Refreezing and Signatures of Retreat Observed at Kamb Ice Stream Grounding Zone,” published in March 2 at Geoscience of nature.
The paper reports results from a 2019 field campaign in the Kamb Ice Stream supported by Antarctic New Zealand and other New Zealand research agencies, led by Christina Hulbe, a professor at the University of Otago, and colleagues. Through 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 mission and develop Icefin. Schmidt’s Planetary Habitability and Technology Lab has been developing Icefin for nearly a decade, starting at the Georgia Institute of Technology.
Combined with recently published surveys of the rapidly changing Thwaites Glacier — explored at the same time as a second Icefin vehicle — the research is expected to improve models of sea-level rise by providing the first high-resolution views of ice, ocean and sea interactions bottom in glacial systems in contrast to the West Antarctic Ice Sheet.
Thwaites, which is exposed to warm ocean currents, is one of the most unstable glaciers on the continent. The Kamb Ice Stream, where the ocean is very cold, has been stagnant since the late 1800s. The Kamb currently offsets some of the ice loss from West Antarctica, but if reactivated it could increase the region’s contribution to sea level rise of the sea by 12%.
“Antarctica is a complex system and it is important to understand both ends of the spectrum — systems that are already undergoing rapid change as well as those quieter systems where future change poses a risk,” Schmidt said. “Observing Kamb and Thwaites together helps us learn more.”
NASA funded the development of Icefin and the Kamb probe to extend ocean exploration beyond Earth. Sea ice like that found in the rift may be analogous to conditions on Jupiter’s icy moon Europa, the target of NASA’s Europa Clipper orbiter scheduled to launch in 2024. Later lander missions may one day search directly for microbial life in the ice.
The Icefin carries a full complement of oceanographic instruments in a modular chassis over 12 feet long and less than 10 inches in diameter. It came down to a tether through a borehole that the New Zealand team drilled through the warm water ice shelf.
During three dives spanning more than three miles near the grounding zone where the Kamb transitions to the floating Ross shelf, Icefin mapped five rifts — climbing one — and the sea floor, while recording water conditions such as temperature, pressure and salinity.
The team observed several ice features that provide valuable information about water mixing and melting rates. They included golf ball-like dimples, ripples, vertical bars, and the most “strange” formations near the top of the crack: ice spheres and finger-like protrusions that look like brinjals.
The ice pumping seen in the crevasse likely contributes to the relative stability of Ross Glacier – the world’s largest by area, the size of France – compared to Thwaites Glacier, the researchers said.
“It’s a way that these large ice shelves can protect and heal themselves,” said Peter Washam, a polar oceanographer on the Icefin science team and second author of the paper. “Much of the melting that occurs deep near the grounding line, the water then refreezes and accumulates on the ice floor as sea ice.”
On the sea floor, Icefin mapped parallel sets of ridges that researchers believe are impressions left behind by ice-shelf rifts — and a record of 150 years of activity since Kamb Stream became stagnant. As the grounding line receded, the ice shelf thinned, causing the cracks to drift apart. The slow movement of the ice over time shifted the cracks seaward of the ridges.
“We can look at these features of the seafloor and connect them directly to what we saw at the base of the ice,” said Lawrence, the paper’s lead author, now a program director and planetary scientist at Honeybee Robotics. “We can, in a way, reset the process.”
In addition to Lawrence, Washam and Schmidt, Cornell co-authors on the research are Senior Research Engineers Matthew Meister, who led the Icefin engineering team, and Andrew Mullen. Research Engineer Daniel Dichek; and program manager Enrica Quartini. Schmidt’s team also includes engineering researcher Frances Bryson and at Georgia Tech PhD students Benjamin Hurwitz and Anthony Spears.
New Zealand partners at 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 Planetary Science and Technology program from the Analog Research Project RISE UP (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 the New Zealand Antarctic Science Platform, the US Antarctic Program and the Victoria University of Wellington Warm Water Drilling Initiative.
