Argo the robot float has given Antarctic researchers a rare view of the frozen south – from below massive ice shelves.
For nearly three years, it measured the temperature and salinity of the ocean underneath floating ice shelves in East Antarctica.
According to the CSIRO, the float, equipped with oceanographic sensors, travelled on a 300-kilometre journey between the Denman and Shackleton ice shelves during which it disappeared under the ice on the first-ever ocean transect (path) beneath an East Antarctic ice shelf.
“We got lucky,” said oceanographer Dr Steve Rintoul from CSIRO, which is in partnership with the Australian Antarctic Program Partnership at the University of Tasmania.
“Our 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.”
ROBOT FLOAT ROLE
The CSIRO says the Argo data shows the Shackleton ice shelf (the most northerly in East Antarctica) is not yet exposed to warm water capable of melting it and is therefore less vulnerable.
But the Denman Glacier, which can add to a global 1.5 metre sea level rise, is being reached by warm water from underneath; small changes in the thickness of the warm water layer could drive much higher melt rates, the CSIRO explains.
Argo can measure factors that can control the melt rate of ice shelves and this data can be used to better predict 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,” Dr Rintoul says.
“This, in turn, would help reduce the largest uncertainty in estimates of future sea level rise,” he said.
Partnership leader Prof Delphine Lannuzel sampled the ocean near the ice shelves during a trip early in 2025.
“Against the enormity of such a wild region, this is an amazing story of the little float (Argo) that could,” she says.
“Under incredibly testing conditions, a relatively tiny instrument delivered us a wealth of invaluable information.”
BACKGROUNDER
Rising sea levels are a a threat to hundreds of millions of people living next to the water including low-lying islands, deltas and coastal cities.
Part of the Antarctic Ice Sheet rests on bedrock below the current sea level and may be vulnerable to warming waters; most of the vulnerable ice is in East Antarctica, which was thought to be isolated from warm water but new observations reveal that large volumes of ice in that area may be at risk.
The stability of the Antarctic Ice Sheet depends on floating ice shelves around the edge of Antarctica. As glaciers flow from the frozen continent to the sea, they float and form ice shelves.
These shelves act like buttresses to resist the flow of ice from Antarctica to the ocean.
If the ice shelves weaken or collapse, more ice flows off the continent into the ocean and cause the sea level to rise.
The process driving melt in ice shelf cavities is very challenging to observe; floats like Argo that drift with ocean currents, periodically rising to the surface to collect a profile of temperature and salinity, are an option. Source: CSIRO
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