12 December 2025
For the first time ever, a robotic float has survived a journey under an East Antarctic ice shelf to deliver unprecedented ocean data.
Image: Pete Harmsen/Australian Antarctic Division
The Argo float disappeared under the ice and survived to send back the first-ever ocean transect beneath an East Antarctic ice shelf.
A robotic float has measured the temperature and salinity from parts of the ocean never sampled before – underneath massive floating ice shelves in East Antarctica.
For two-and-a-half years, an Argo float equipped with oceanographic sensors collected nearly 200 profiles of the ocean on a 300km journey spanning the Denman and Shackleton ice shelves.
During that time, it disappeared under the ice and survived to send back the first-ever ocean transect beneath an East Antarctic ice shelf.
“We got lucky,” said oceanographer Dr Steve Rintoul from CSIRO, Australia’s national science agency, partner with the Australian Antarctic Program Partnership at the University of Tasmania.
“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.”
The measurements reveal the Shackleton ice shelf (the most northerly in East Antarctica) is, for now, not exposed to warm water capable of melting it from below, and therefore less vulnerable.
However, the Denman Glacier, with its potential 1.5m contribution to global sea level rise, is delicately poised: warm water is reaching underneath, and small changes in the thickness of the warm water layer could drive much higher melt rates that lead to unstable retreat.
The transfer of heat from the ocean to the ice depends on the ocean conditions in the 10m-thick ‘boundary layer’ immediately below the ice shelf.
“A great advantage of floats is that they can measure the properties of the boundary layer that control the melt rate,” said Dr Rintoul.
“The float measurements will be used to improve how these processes are represented in computer models, reducing the uncertainty in projections of future sea level rise.
“Deploying more floats along the Antarctic continental shelf would transform our understanding of the vulnerability of ice shelves to changes in the ocean.
“This, in turn, would help reduce the largest uncertainty in estimates of future sea level rise,” he said.
Leader of the Australian Antarctic Program Partnership, Professor Delphine Lannuzel, sampled the ocean near the ice shelves during the Denman Marine Voyage earlier this year.
“Against the enormity of such a wild region, this is an amazing story of the little float that could,” she said.
“Under incredibly testing conditions, a relatively tiny instrument has delivered us a wealth of invaluable information.”