The European Space Agency’s (ESA) CryoSat mission has discovered that Antarctica has lost an area of underwater ice the size of London, UK, because the warming ocean beneath the floating margins is working away at the seabed ice.
A research team led by Dr Hannes Konrad from the Centre for Polar Observation and Modelling at the University of Leeds, UK, shows that between 2010 and 2017 the warming ocean melted 1,463km2 of underwater ice.
Most Antarctic glaciers flow into the ocean in deep submarine troughs. The grounding line – where the base leaves the seabed and begins to float – is typically a kilometre or more below sea level and are inaccessible even to submersibles, so remote methods for detecting them are extremely valuable..
A paper published in Nature Geoscience describes how CryoSat was used to map the grounding line motion along 16,000km of Antarctic coastline.
What did the researchers find?
The team found that the biggest changes are seen in West Antarctica, where over a fifth of the ice sheet had retreated across the seafloor faster than the pace of deglaciation since the last Ice Age.
Konrad said: “Our study provides clear evidence that retreat is happening across the ice sheet due to ocean melting at its base, and not just at the few spots that have been mapped before now.
“This retreat has had a huge impact on inland glaciers because releasing them from the seabed removes friction, causing them to speed up and contribute to global sea-level rise.”
CryoSat is designed to measure changes in the ice-sheet elevation, however, these can be translated into horizontal motion at the grounding line through the use of the Archimedes principle and knowledge of the glacier and seafloor.
The retreat of the Thwaites Glacier in West Antarctica has sped up, while the retreat at the neighbouring Pine Island Glacier – until recently one of the fastest retreating on the continent – has halted, suggesting that the warming ocean and ocean melting at its base has paused.
Konrad added: “These differences emphasise the complex nature of ice-sheet instability across the continent, and being able to detect them helps us to pinpoint areas that deserve further investigation.”
ESA CryoSat mission manager Tommaso Parrinello added: “Even though CryoSat is now approaching its eighth year in orbit – more than twice its intended lifetime – it’s wonderful to see that the mission is still making measurements of the highest quality and enabling new discoveries in polar science.”