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A robotic float has measured the temperature and salinity from parts of the ocean never sampled before \u2014 underneath massive floating ice shelves in East Antarctica.<\/p>\n
For two-and-a-half years, an Argo float equipped with oceanographic sensors collected nearly 200 profiles of the ocean on a 300-kilometre journey spanning the Denman and Shackleton ice shelves.<\/p>\n
During that time, it disappeared under the ice and survived to send back the first-ever ocean transect beneath an East Antarctic ice shelf.<\/p>\n
\u201cWe got lucky,\u201d said oceanographer Dr Steve Rintoul from CSIRO, Australia\u2019s national science agency, partner with the Australian Antarctic Program Partnership at the University of Tasmania.<\/p>\n
\u201cOur 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.<\/p>\n
\u201cThese unprecedented observations provide new insights into the vulnerability of the ice shelves.\u201d<\/p>\n
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.<\/p>\n
However, the Denman Glacier, with its potential 1.5-metre 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.<\/p>\n
The transfer of heat from the ocean to the ice depends on the ocean conditions in the 10-metre thick \u2018boundary layer\u2019 immediately below the ice shelf.<\/p>\n
\u201cA great advantage of floats is that they can measure the properties of the boundary layer that control the melt rate,\u201d said Dr Rintoul.<\/p>\n
\u201cThe 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.<\/p>\n
\u201cDeploying more floats along the Antarctic continental shelf would transform our understanding of the vulnerability of ice shelves to changes in the ocean.<\/p>\n
“This, in turn, would help reduce the largest uncertainty in estimates of future sea level rise,\u201d he said.<\/p>\n
Leader of the Australian Antarctic Program Partnership, Prof Delphine Lannuzel, sampled the ocean near the ice shelves during the Denman Marine Voyage earlier this year.<\/p>\n
\u201cAgainst the enormity of such a wild region, this is an amazing story of the little float that could,\u201d she said.<\/p>\n
\u201cUnder incredibly testing conditions, a relatively tiny instrument has delivered us a wealth of invaluable information.\u201d\u00a0<\/p>\n
Published in Science Advances: Rintoul S.R., van Wijk E.M., Herraiz-Borreguero, L. and Rosevear, M.G. (2025) ‘Circulation and ocean\u2013ice shelf interaction beneath the Denman and Shackleton Ice Shelves’, Sci. Adv. 11, 10.1126\/sciadv.adx1024<\/p>\n
The authors are from CSIRO, the Australian Antarctic Program Partnership and the Institute for Marine and Antarctic Studies at the University of Tasmania.\u00a0They acknowledge support from Australia\u2019s Integrated Marine Observing System (IMOS) \u2014 IMOS is enabled by the National Collaborative Research Infrastructure Strategy (NCRIS).<\/p>\n
BACKGROUND INFORMATION<\/p>\n
Sea level rise poses a threat to hundreds of millions of people living on the coast, including low-lying islands, deltas and coastal cities. How much Antarctica will contribute to sea level rise<\/a> is the largest uncertainty in future projections.<\/p>\n Part of the Antarctic Ice Sheet rests on bedrock below present-day sea level and is potentially vulnerable to changes in the surrounding ocean. Most of the vulnerable ice is in East Antarctica, which was thought to be isolated from warm water and therefore unlikely to melt. But new observations show that large volumes of ice in East Antarctica are potentially at risk.<\/p>\n The stability of the Antarctic Ice Sheet depends on the floating ice shelves around the edge of Antarctica. As glaciers flow from the Antarctic continent to the sea, they start to float, forming ice shelves.<\/p>\n The ice shelves act like buttresses that resist the flow of ice from Antarctica to the ocean. If the ice shelves weaken or collapse, more ice flows off the continent and into the ocean, causing sea level to rise. The key factor determining the fate of the Antarctic ice sheet \u2013 and therefore the rate of sea level rise \u2013 is how much ocean heat reaches the base of the floating ice shelves.<\/p>\n