The device launched by Australian scientists carried out the “first ocean transect under an ice shelf in East Antarctica”, providing valuable information on the vulnerability of these natural barriers to polar ice melt. A robotic float measured the temperature and salinity of previously unsampled ocean areas located under immense floating ice shelves in East Antarctica.
In fact, for two and a half years, this Argo float, equipped with oceanographic sensors, collected unprecedented data during a 300-kilometre journey across the Denman and Shackleton ice shelves, as detailed in a statement from CSIRO, Australia’s national science agency, and the University of Tasmania’s Australian Antarctic Program Association (AAPP) at the University of Tasmania.
For eight months, the bright yellow cylinder simply disappeared under the ice. However, it remained intact to transmit the ‘first ocean transect under an East Antarctic ice shelf’.
A ‘goldmine of invaluable information’
Professor Delphine Lannuzel, head of the AAPP, is also surprised. ‘Given the immensity of this wild region, it is an extraordinary story, that of a small float that rose to the challenge. In extremely difficult conditions, a relatively tiny instrument has provided us with a goldmine of invaluable information,’ she added.
What is a transect?
The term ‘transect’ is a scientific practice that consists of ‘travelling through and studying a space along a linear trajectory’ (definition by Nicolas Tixier, ‘Performascope’ Lexicon, University of Grenoble Alpes, 2021).
The measurements collected by the float reveal that the Shackleton Ice Shelf, the northernmost ice shelf in East Antarctica, is not currently exposed to warm waters that could melt it from below. It is therefore less vulnerable to the consequences of climate change.
Denman’s, on the other hand, is in a delicate situation. Warm waters reach the bottom, so small variations in the thickness of the water layer could cause much faster melting, leading to unstable retreat.
But why should we care about what happens in these distant regions? As we know, rising sea levels threaten hundreds of millions of people living on the coast, especially on low-lying islands, deltas and coastal cities. However, Antarctica’s contribution to this rise is the main uncertainty in future projections.
Weakened natural barriers
In East Antarctica, part of the ice sheet rests on a bedrock below the current sea level, making it potentially vulnerable to variations in the surrounding ocean. Its stability depends on the floating ice shelves that surround the continent, as these act as barriers that block the flow of continental ice into the ocean.
If these shelves weaken or collapse, more ice will break off the continent and pour into the ocean, causing sea levels to rise. The determining factor for the future of the Antarctic ice sheet — and therefore the rate of sea level rise — is the amount of ocean heat reaching the base of the floating ice shelves.
However, the transfer of heat from the ocean to the ice depends on ocean conditions in the 10-metre-thick “boundary layer” immediately below the ice barrier. “One of the great advantages of floats is that they allow us to measure the properties of the boundary layer that control the rate of melting,” Dr Rintoul points out.
The measurements from the floats will therefore serve to ‘improve’ the representation of these processes in computer models, thereby reducing ‘the uncertainty of projections’ about future sea level rise, the researcher anticipates. According to him, this is provided that ‘more floats’ are deployed along the Antarctic continental shelf.
