Hidden geological formations that hold vast amounts of water under Antarctica's ice sheet could be causing it to shrink more quickly, a new Australian study suggests.
Researchers have mapped the location of sedimentary basins, which behave like sponges and soak up water and sediment when glaciers are growing.
But they have the opposite effect when glaciers are in retreat, as they are in Antarctica due to climate change.
As ice mass reduces, it eases the downward pressure on the basins and they can quickly release the water they hold, speeding up the rate of ice loss and potentially leading to faster sea level rises.
The bad news is sedimentary basins have been found beneath some of the continent's fastest retreating glaciers, including the so-called "doomsday" Thwaites Glacier, along with the Pine Island Glacier and the Totten Glacier.
"They all have sedimentary basins at its upstream," says study author Lu Li, a geophysicist and PhD candidate at the University of Western Australia.
"Sedimentary basins are also found at potentially vulnerable ice streams including Siple Coast Ice stream, Recovery Glacier, Cook Ice Shelf Glacier, Ninnis Glacier."
A separate study published last month found the Florida-sized Thwaites Glacier and its neighbour, the Pine Island Glacier, may now be shedding ice faster than at any point in the past 5500 years.
Mr Li can't say how much faster ice streams might retreat due to the effect of the sedimentary basins but he says the findings are sobering and demonstrate the need for urgent action to limit the emissions fuelling climate change.
"We need to work with the ice sheet modelling community to understand this effect on future ice sheet change," he says.
The study has been published in the journal Nature Geoscience.
