Antarctic Robot Survives Eight-Month Odyssey Under Ice Shelves

A Remarkable Accident Turns Into Scientific Goldmine

What began as a disappointing drift away from its intended research site became one of the most valuable Antarctic discoveries in recent years. An Argo float equipped with temperature and salinity sensors was supposed to be surveying the ocean around the Totten Glacier in eastern Antarctica, but to researchers' initial disappointment, it rapidly drifted away from this region. Soon it reappeared further west, near ice shelves where no ocean measurements had ever been made, drifting in remote and wild seas for two-and-a-half years and spending about nine months beneath the massive Denman and Shackleton ice shelves before surviving to send back new data from parts of the ocean that are usually difficult to sample.

During an eight-month period, the float measured temperature and salinity profiles from the seafloor to the ice shelf base every five days, collecting 195 profiles over 2.5 years, many of which came from never-before-sampled regions in East Antarctica. This tiny robot accomplished what no human expedition, ship, or sensor array had ever managed before.

Navigation Without GPS Creates Detective Work

Submersion essentially disabled the float's GPS capabilities, but the researchers found a way to infer where measurements were made by noting when the float bumped its head on the ice. 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. Scientists had to become detectives, and each time the instrument bumped the ice above, it recorded the depth of the ice base, then researchers matched those ice-draft measurements with satellite data to map where the float had travelled beneath the frozen ceiling.

The challenge of studying these regions cannot be overstated. Ice shelves can be hundreds to thousands of feet thick, making it incredibly challenging for scientists to study exactly how ice shelves collapse. While it is possible to drill a hole through the ice and lower oceanographic sensors, this is expensive and rarely done, so very few measurements have been made in ice shelf cavities.

Tale of Two Ice Shelves Reveals Critical Differences

The data revealed dramatically different conditions beneath the two ice shelves. Shackleton, the northernmost of East Antarctica, appears relatively safe for now, with no warm water detected beneath it that could trigger rapid melt from below. However, Denman Glacier tells a different story, with the potential to raise global sea levels by 1.5 metres and already being touched by warm water.

According to the new measurements, even small changes in the thickness of that warm-water layer could sharply accelerate melting and push the glacier toward unstable retreat. If the ice retreated further, they would be in an unstable configuration where further melt was irreversible, and once this process of unstable retreat begins, we are committed—it may take centuries for the full sea-level rise to be realised, but there's no going back.

Blueprint for Future Climate Understanding

Deploying more floats along the Antarctic continental shelf would transform our understanding of the vulnerability of ice shelves to changes in the ocean, which in turn would help reduce the largest uncertainty in estimates of future sea level rise. Between the Denman and Totten glaciers, they hold a huge volume of ice equivalent to five metres of global sea level rise, and while the West Antarctic ice sheet is at greater risk of imminent melting, East Antarctica holds a much larger volume of ice.

This accidental journey demonstrates how innovative approaches to climate science can emerge from unexpected circumstances. The success of this lone robot offers hope that similar deployments could provide the comprehensive data needed to better predict and prepare for our planet's changing ice sheets.