Water is flowing across Antarctica in vast rivers, lakes and waterfalls and has been for decades, scientists have discovered.
While temporary meltwater streams have been encountered before by polar explorers like Ernest Shackleton, it was thought liquid water was relatively rare because the continent is so cold.
However a new study of aerial photography and satellite images found “widespread drainage of meltwater” as far south as 600km (375 miles) from the South Pole and as high as 1,300m above sea level – about the same height as Ben Nevis.
This included rivers of up to 120km, 80km-long lakes and waterfalls that were 120m across.
The researchers warned the amount of liquid they had found could increase the rate of melting on Antarctica above currently expected levels. If all the continent’s ice was lost, a process that would likely take centuries, this would raise sea levels by about 60m worldwide.
“While Antarctic surface melt ponds are relatively well documented on some ice shelves, we have discovered that ponds often form part of widespread, large-scale surface drainage systems.
“In a warming climate, enhanced surface drainage could accelerate future ice-mass loss from Antarctic, potentially via positive feedbacks between the extent of exposed rock, melting and thinning of the ice sheet.”
Professor Jonathan Kingslake, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory, said their findings had been a surprise.
“This is not in the future – this is widespread now, and has been for decades,” he said.
“I think most polar scientists have considered water moving across the surface of Antarctica to be extremely rare.
“But we found a lot of it, over very large areas.”
The researchers were unable to tell whether the amount of meltwater streams had been increasing over the last 70 years, the period for which images exist, because there was not enough data.
“Looking forward, it will be really important to work out how these systems will change in response to warming, and how this will affect the ice sheets,” Professor Kingslake said.
His colleague, Professor Robin Bell, also of Columbia, added it was likely to increase the rate of ice-loss in the future.
“This study tells us there's already a lot more melting going on than we thought,” she said.
“When you turn up the temperature, it's only going to increase.”
However, in a related study of the Nansen Ice Shelf led by Professor Bell, researchers found that meltwater streams could actually help prevent the break-up of ice by carrying water away.
Water is darker than ice so absorbs more of the sun’s energy, increasing the temperature and therefore the amount of melting. It also has other structural affects which can weaken the ice.
Ice shelves float on the sea, so would not contribute to sea level rise themselves, but they help hold back land glaciers which do.
Research in Greenland has shown that surface meltwater streams also speed up the rate of ice loss, by cutting through glaciers and then lubricating their passage over the ground.
In a commentary in Nature, Dr Alison Banwell, of the Scott Polar Research Institute at Cambridge University, said the overall effect of the newly discovered amount of Antarctic meltwater was unclear.
“The extent to which meltwater production will enhance ice-shelf instability is debatable,” she said.
“It was previously suggested that the development of hundreds of surface lakes could provide the tipping point, which, once reached, would trigger the break-up of an ice shelf.
“If this is true, many ice shelves could be exposed to an ever-increasing risk of break-up, given their already extensive lake coverage.
“However, such a threshold might not be reached if surface water can instead be efficiently exported from the ice shelf to the ocean through large river networks.”
She stressed the need to work out exactly what would happen.
“Given that the Antarctic Ice Sheet contains enough ice to raise global sea levels by 60m, identifying and quantifying the role of all surface and subsurface processes on the potential stability of ice shelves is becoming increasingly important.”
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