Antarctica is a complicated system, and it’s crucial to understand both sides of the spectrum – systems presently experiencing fast change and calmer areas where future change presents a concern

The remotely operated Icefin underwater vehicle, stationed in a tight, seawater-filled crevasse at the base of Antarctica’s largest ice shelf, captured a sudden transformation in its surroundings through its cameras.

The once smooth and cloudy walls made of meteoric ice underwent a dramatic change, turning green and developing a rough texture as they gave way to the salty marine ice.

A U.S.-New Zealand research team identified the shift as proof of “ice pumping,” a process never before directly observed in an ice shelf crevasse but critical to the stability of the shelf, close to where the surface of the Ross Ice Shelf meets Kamb Ice Stream, at a height of nearly 1,900 feet above.

“We were looking at ice that had just melted less than 100 feet below, flowed up into the crevasse and then refrozen,” remarks Justin Lawrence, visiting scholar at the Cornell Center for Astrophysics and Planetary Science. “And then it just got weirder as we went higher up.”

The work published today in Nature Geoscience describes the Icefin robot’s first-ever glimpse into a crevasse and observations revealing more than a century’s worth of geological events under the ice shelf.

In the study, University of Otago professor Christina Hulbe and colleagues present the findings of a 2019 field expedition to the Kamb Ice Stream, which was supported by Antarctica New Zealand.

Thanks to the backing of NASA’s Astrobiology Program, Britney Schmidt, an associate professor of Astronomy and Earth and Atmospheric Sciences at Cornell University, with colleagues was able to participate in the expedition and deploy Icefin. Icefin was developed by Schmidt’s Planetary Habitability and Technology Lab over the course of almost a decade, starting at the Georgia Institute of Technology.

By complementing the recently published studies on the rapidly transforming Thwaites Glacier, which was also examined that season by another Icefin vehicle, this research is anticipated to enhance sea-level rise models. It is the first time that high-resolution observations of interactions between ice, ocean, and the seafloor at divergent glacier systems on the West Antarctic Ice Sheet have been obtained.

Thwaites is one of the most dangerous glaciers on the continent because it is close to warm ocean currents. Since the late 1800s, nothing has moved in Kamb Ice Stream, where the ocean is very cold. Western Antarctica’s ice loss is presently somewhat offset by Kamb, but if it becomes active again, the region’s contribution to sea level rise may climb 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,” Schmidt adds. “Observing Kamb and Thwaites together helps us learn more.”

NASA supported the construction of Icefin and the Kamb mission to expand ocean exploration beyond Earth. Sea ice similar to that discovered in the crevice may be a good indicator of the climate on Jupiter’s icy moon Europa, which NASA’s Europa Clipper orbital mission will explore starting in 2024. One day, lander expeditions in the future could look directly for microbial life in the ice.

Icefin is equipped with an entire suite of oceanographic tools attached to a modular frame that is over 12 feet in length and less than 10 inches in diameter. The vehicle was lowered on a tether through a borehole, which the New Zealand team created by using hot water to drill through the ice shelf.

Icefin mapped five crevasses, including one that was ascending, and the ocean floor over the course of three dives that covered a distance of more than three miles close to the grounding zone where the Kamb shelf changes into the floatable Ross shelf. It also recorded water parameters like temperature, pressure, and salinity.

The team saw different kinds of ice features that tell them important things about how water mixes and how fast it melts. These featured ripples, vertical runnels, dimples like golf balls, and the “weirder” formations towards the top of the crevasse: globs of ice and finger-like protrusions that looked like brinicles.

The Ross Ice Shelf, the biggest in the world by area and the size of France, is more stable than Thwaites Glacier because of ice pumping that was seen in the crevasse, according to the researchers.

“It’s a way these big ice shelves can protect and heal themselves,” adds second author Peter Washam. “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.”

Icefin recorded parallel pairs of ridges on the ocean bottom, which the researchers think are the imprints of ice shelf crevasses and provide a record of 150 years of activity since the Kamb stream stalled. As its grounding line moved away, the ice shelf got thinner, which made the cracks disappear. The crevasses moved away from the ridges toward the sea due to the ice’s sluggish migration over time.

“We can look at those seafloor features and directly connect them to what we saw on the ice base,” adds Lawrence, the paper’s lead author, now a program manager and planetary scientist at Honeybee Robotics. “We can, in a way, rewind the process.”

Source: 10.1038/s41561-023-01129-y