Over the last year, a team of autonomous ocean robots has successfully traveled under an ice sheet and returned to report long-term observations, the University of Washington (UW) has announced.

A partnership between a number of entities including the University of Washington’s College of the Environment, the UW Applied Physics Laboratory, the Lamont-Doherty Earth Observatory of Columbia University, the Korean Polar Research Institute and Paul G. Allen Family Foundation, the robotic mission has traveled under the ice shelf 18 times, and has routinely reached more than 25 miles into the cavity.

“This is the first time any of the modern, long-endurance platforms have made sustained measurements under an ice shelf,” says Craig Lee, a UW professor of oceanography and member of the Applied Physics Laboratory.

“We made extensive measurements inside the cavity. Gliders were able to navigate at will to survey the cavity interior, while floats rode ocean currents to access the cavity interior.”

The project not only looks to showcase this technology, but also gather more data from the underside of ice shelves that are buttressing the much larger ice sheets.

Additionally, being able to directly observe how warmer seawater interacts with the underside of ice shelves provides the opportunity to improve models of ice sheet dynamics in Antarctica and Greenland, which hold the biggest unknowns for global sea level rise, according to UW.

“Some ice sheets terminate in large ice shelves that float out over the ocean, and those act as a buttress. If the ice shelves collapse or weaken, due to oceanic melting, for example, the ice sheets behind them may accelerate toward the sea, increasing the rate of sea level rise,” Lee explains.

In late 2017 when this mission began, the goal was to test a new approach for gathering data under an ice shelf. On Jan. 24, 2018, devices were dropped from the Korean icebreaker R/V Araon, and this week, two Seaglider AUVs reached the milestone of one year of continuous operation around and under the ice shelf.

Similar missions of this kind have been done before, as in 2009, 2014 and 2018, robot submarines Autosub3 and Boaty McBoatface—operated by the British Antarctic Survey—successfully completed 24- to 48-hour voyages. While these missions surveyed similar distances into the cavity, the samples were over shorter periods due to the need for a ship support.

Conversely, the UW-led team’s technology features smaller, lighter devices that can operate on their own for more than a year without any ship support. The team notes that its experimental technique first moored three acoustic beacons to the seafloor to allow navigation under the ice shelf. Then, three Seagliders were sent to use preprogrammed navigation systems to travel under the ice shelf to collect data.

During the mission, four UW-developed EM-APEX floating instruments were also deployed. The instruments can drift with the currents at preselected depths above the bottom, or below the top of the cavity, while periodically bobbing up and down to collect more data.

All four of the instruments successfully traveled deep under the ice shelf with the heavier, saltier water near the seafloor. Three were flushed out with fresh meltwater near the top of the ice cavity about six to eight weeks later, while the remaining one recently reappeared on Jan. 5.

The fleet of robots reached a number of milestones over the last year during their deployment, including: a Seaglider reached a maximum distance of 31 miles from the edge beneath Dotson Ice Shelf in West Antarctica; the Seagliders made 30 surveys along the face of the ice shelf; and, after one year, two out of three Seagliders are reporting back.

Researchers are now analyzing the data for future publication, so that they can have a better understanding of how seawater interacts with the ice shelves and improve models of ice sheet behavior.