What Missing Antarctic Robot Just Revealed About Polar Ice and Climate Change

As the planet warms and land-based ice makes its way to the oceans, sea levels will rise, threatening islands and coastal regions. Climate scientists model potential changes into the future, but there are uncertainties in those models, primarily the impact of Antarctic ice.

The oceans play an important role in sequestering carbon and holding onto excess heat. As the oceans warm, their capacity to melt ice shelves and glaciers increases. Scientists rely on a network of oceanic sensors to gather data on how global temperature is changing, and how it will continue to change, into the future. That network includes approximately 3,600 Argo floats, oceanic robots equipped with sensors to collect real-time data like temperature and salinity.

In September 2020, researchers deployed an Argo float near Totten Glacier in eastern Antarctica. The robotic float quickly drifted away from its intended location and reappeared farther west, in a place where no oceanic measurements had ever been made. Then the float vanished beneath the ice of Shackleton ice shelf. Scientists thought the instrument was lost forever, but eight months later it reemerged, having collected rare scientific data from a part of the planet never measured before.

A missing Antarctic robot reappeared with rare scientific data

As glaciers move from the Antarctic interior and reach the sea, they float and form ice shelves. When they are stable, those shelves act like a barrier, preventing ground-based ice from flowing into the ocean. If they weaken or collapse, grounded ice moves forward to take its place, and sea levels rise. The defining factor of how quickly ice retreats is how much heat reaches the underside of the ice shelf.

Getting measurements of heat beneath an ice shelf can be difficult, in large part because ice shelves can be between 300 and 3,000 feet thick. Researchers can drill holes through the ice to reach the water below, but that’s difficult and expensive, which is why these accidental robotic measurements are so valuable.

Argo floats are designed to drift at ocean depths between one and two kilometers (0.62 to 1.24 miles), then resurface every 10 days or so. They collect data from throughout the water column and, when they resurface, transmit that data to orbiting satellites.

Antarctic researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), the Australian Antarctic Program Partnership, and the Institute for Marine and Antarctic Studies at the University of Tasmania deployed the float to measure how much heat was reaching the underside of Totten Glacier. It has enough ice that, if it all melted or fell into the sea, it would raise global sea levels by 11.5 feet. Instead, the robot drifted to Denman Glacier, a smaller (but still huge) glacier with enough ice to raise global sea levels about five feet.

The float spent approximately eight months floating beneath the previously unmeasured Antarctic ice. The results of the unintended study were published in the journal Science Advances.

"We got lucky," said lead author Dr. Steve Rintoul, in a Dec. 6 statement. "Our intrepid float drifted beneath the ice and spent eight months under the Denman and Shackleton ice shelves, collecting profiles from the seafloor to the base of the ice every five days. These unprecedented observations provide new insights into the vulnerability of the ice shelves."

How protecting polar ice protects the rest of the planet

The float reached the continental shelf of the Denman Glacier in September 2020 and took measurements of temperature and salinity every five days until March 2023. Over this 2.5-year period, the robotic sensor collected nearly 200 profiles, spanning the entire width of the Shackleton system.

"Against the enormity of such a wild region, this is an amazing story of the little float that could," said Professor Delphine Lannuzel, leader of the Australian Antarctic Program Partnership. "Under incredibly testing conditions, a relatively tiny instrument has delivered us a wealth of invaluable information."

The data revealed that the Shackleton ice shelf is insulated from warm subsurface water. For now, at least, the Shackleton ice shelf appears to be more or less stable. The Denman Glacier, by contrast, is exposed to warm water which is causing the ice to melt. Argo float data suggests the glacier is at risk and, if the warm water layer got a little bit thicker, it could increase warming, melting, and ice flow into the ocean.

Getting that information was no easy task. Because the robot was trapped beneath the ice for months, it couldn’t surface and transmit its location to orbiting satellites. When it finally resurfaced and delivered its data, scientists couldn’t be sure where the float was when it was making its measurements. Fortunately, they had a clue.

"We had to do some detective work to determine where the float measurements were made," Rintoul said. "Each time the float bumped its head on the ice, it provided a measurement of the depth of the ice shelf base, or ice draft. We could compare the ice draft measured by the float to satellite measurements of draft to work out the path of the float beneath the ice."

The float revealed that Totten (the intended target) and Denman (where the float ended up) are vulnerable to warming and melting. Combined, the glaciers hold enough ice to raise global sea levels by more than 16 feet. Right now, both glaciers are stabilized by the bedrock on which they sit, but if ice shelf melting increases, it would put them into an unstable configuration and increased melting would become irreversible.

Understanding the Antarctic ocean environment is crucial to predicting the future of climate change. To that end, scientists recommend ramping up the network of Argo floats and other sensors. "Deploying more floats along the Antarctic continental shelf would transform our understanding of the vulnerability of ice shelves to changes in the ocean," Rintoul continued. "This, in turn, would help reduce the largest uncertainty in estimates of future sea level rise."

See the effects of future climate change up close and personal in The End is Nye, streaming now on SYFY.