⚠️ A robot, missing for 9 months, resurfaces with an alarming message

The mission had begun as a routine analysis of a glacier. It turned into an unplanned expedition into the heart of the most inhospitable regions of the white continent.

A simple oceanographic float, used to study the Totten Glacier, drifted for two and a half years under the ice before reappearing hundreds of miles (kilometers) away, laden with unprecedented data. Its unplanned journey under the Denman and Shackleton ice shelves offers a unique opportunity to discover the still unknown processes that are shaping the future of the polar ice sheet.


These accidental observations are of considerable scientific value. They come from an area where direct measurements were previously virtually nonexistent, due to the thickness of the ice and the remoteness. The instrument, an autonomous Argo-type profiler, collected temperature and salinity profiles for nine months under the sea ice, revealing the presence of water with different characteristics beneath these two major structures.

This odyssey highlights how chance and the robustness of proven technologies can sometimes reveal still unknown areas of climate research.

The valuable drift of a lost instrument

The instrument behind this discovery is an Argo float, an oceanographic robot designed to drift freely. Programmed to dive to depths of up to 1.2 miles (two kilometers) and surface periodically, these devices usually transmit their data via satellite every ten days. This one, deployed to monitor the waters around the Totten Glacier, quickly left the intended area, carried away by currents. Researchers then believed it lost, until it resurfaced far to the west, near the Denman and Shackleton ice shelves.

Its long nine-month silence is explained by the permanent presence of ice above it, preventing it from communicating with satellites. During this period, it continued its measurement program, recording the temperature and salinity of the water from the seabed to the base of the ice at regular intervals. Each attempt to surface resulted in contact with the ice shell, thus providing, unintentionally, a valuable measurement of its thickness at that precise location.

Analyzing this data required particular ingenuity. Without GPS positions, scientists cross-referenced the ice thickness measurements collected by the robot with maps established by satellite. This comparison allowed them to reconstruct the float's most likely path under the ice shelf, much like tracing a route from scattered clues. This methodology, described in Science Advances, validated the instrument's journey and the geographic origin of each sample.

Two glaciers, two contrasting destinies

The transmitted data paint a contrasting picture of ice stability in this part of East Antarctica. Beneath the Shackleton Ice Shelf, the northernmost one, the measurements indicate an absence of warm water capable of causing significant basal melting. This structure therefore appears, for the moment, relatively protected from the most destructive oceanic incursions. This situation offers a respite, but requires continuous monitoring to detect any future changes.

The discovery is more alarming for the Denman Glacier. The profiler clearly identified the presence of a layer of warmer water circulating beneath its floating part. This water is already causing melting at the base. Scientists believe the configuration is precarious: a slight increase in the thickness of this warm water layer could significantly accelerate the disintegration process, committing the glacier to a potentially irreversible retreat.

The stakes are high. The Denman Glacier alone contains enough ice to raise global sea levels by about 5 feet (1.5 meters) if it were to melt completely. Combined with the Totten Glacier, whose potential is estimated at 11.5 feet (3.5 meters), these two giants of East Antarctica represent a major long-term threat. Their confirmed vulnerability to warm ocean water requires integrating these new parameters into sea level rise forecast models.

To go further: What is this "warm" water melting Antarctic ice?

It must be understood that "warm" is a relative term. In Antarctica, surface water is generally frozen. The so-called "warm" water comes from deeper ocean layers and circulates over the continental shelf. Its temperature may be only a few degrees above the freezing point (which is lowered by pressure and salinity under the ice).

Even at +1°C or +2°C, this water has sufficient thermal energy to melt the base of the ice on contact. The process is constant and massive, as vast areas of ice are in contact with the ocean. The circulation of this water is therefore the main driver of the melting of ice shelves from below, long before the ambient air has any effect.