
Before the end of the century, rising temperatures could trigger an influx of warm water beneath Antarctica’s second-largest ice shelf – and once it begins, researchers say there’s ‘no going back.’

The phenomenon would cause the ice to lose contact with the seafloor, which has so far acted as a natural brake to slow the ice flow.

Scientists say they've already detected the first signs of the process, and once underway, it will cause the ice to shed at a much faster rate, dramatically shrinking the massive Filchner-Ronne Ice Shelf.

New simulations reveal that rising air temperatures over the Weddell Sea could make for less sea ice, triggering processes that permanently do away with the cold water barrier (illustrated). Once underway, the process will cause the ice to shed at a much faster rate

WHAT COULD HAPPEN During the autumn and winter, the sea ice releases massive amounts of salt, which in turn creates a barrier of cold, salty water (about -2 degrees C) that protects the ice shelf from an inflow of warmer water (.8 degrees) transported by the Weddell Gyre. But, the new simulations reveal that rising air temperatures over the Weddell Sea could make for less sea ice, triggering processes that permanently do away with the cold water barrier. The melting beneath the ice shelf will cause its grounding line to shift further south, eliminating direct contact between the ice and the seafloor. While frictional contact has kept the ice flow in check to date, the phenomenon will accelerate once that effect is lost. Once underway, the process will cause the ice to shed at a much faster rate, dramatically shrinking the massive Filchner-Ronne Ice Shelf. Advertisement

In a new study, researchers at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research used the Bremerhaven Regional Ice-Ocean Simulations ice-ocean model to understand the effect of a self-amplifying meltwater feedback cycle beneath the Filchner-Ronne, in the Weddell Sea.

The phenomenon has already been seen in the nearby Amundsen Sea, where they now say the ‘inflow of heat cannot be stopped.’

Sea ice plays a critical role in the survival of the Antarctic ice shelves, the researchers explain.

During the autumn and winter, the sea ice releases massive amounts of salt, which in turn creates a barrier of cold, salty water (about -2 degrees C) that protects the ice shelf from an inflow of warmer water (.8 degrees) transported by the Weddell Gyre.

But, the new simulations reveal that rising air temperatures over the Weddell Sea could make for less sea ice, triggering processes that permanently do away with the cold water barrier.

‘We can already see the first signs of this trend today,’ said lead author Dr Hartmut Hellmer, an oceanographer at the AWI.

‘First of all, less sea ice is forming in the region, and secondly, oceanographic recordings from the continental shelf break confirm that the warm water masses are already moving closer and closer to the ice shelf in pulses.’

According to the researchers, this could mark the beginning of ‘irrevocable transformation’ in the southern Weddell Sea – and they say the effects will likely be noticeable by 2070.

In a new study, researchers used the Bremerhaven Regional Ice-Ocean Simulations ice-ocean model to understand the effect of a self-amplifying meltwater feedback cycle beneath the Filchner-Ronne (pictured), in the Weddell Sea

‘Our simulations show that there will be no turning back once the warm water masses find their way under the ice shelf, since their heat will accelerate the melting at its base,’ Hellmer says.

‘In turn, the resulting meltwater will produce an intensified overturning, which will suck even more warm water from the Weddell Gyre under the ice.

‘As such, according to our calculations, the hope that the ocean would someday run out of heat won’t pan out in the long run.’

Before the end of the century, rising temperatures could trigger an influx of warm water beneath Antarctica’s second-largest ice shelf (the Filchner, pictured) – and once it begins, researchers say there’s ‘no going back’

Their model includes data on future winds and temperatures in the Antarctic, based on the assumption that atmospheric carbon dioxide will hit 700 parts per million by the year 2100.

But, even if the world limits warming to 2 degrees Celsius in the next few decades, it ‘won’t be enough to save the Filcher-Ronne Ice Shelf.’

The melting beneath the ice shelf will cause its grounding line to shift further south, eliminating direct contact between the ice and the seafloor.

While frictional contact has kept the ice flow in check to date, the phenomenon will accelerate once that effect is lost.

CHANNELS AS TALL AS THE EIFFEL TOWER FOUND BENEATH THE FILCHNER-RONNE ICE SHELF In 2013, scientists discovered huge 250 metre high ice channels beneath Antarctica - and, they could be speeding up melting of the ice shelf. The channels are almost as tall as the Eiffel Tower and are thought to stretch hundreds of kilometres along the ice shelf. The British researchers used satellite images and airborne radar measurements to reveal the channels under the Filchner-Ronne Ice Shelf in West Antarctica. The ice sheld channel is clearly visible on the MODIS Mosaic of Antarctica image map. The predicted flow route of water beneath the grounded ice sheet aligns with the initiation of the ice shelf channel. The dashed line marks the point at which the ice starts to float When the meltwater flowing under the ice sheet enters the ocean beneath, it causes a plume of ocean water to form, which then melts out the vast channels under the ice shelf. Previously, it was thought that water flowed in a thin layer beneath the ice sheet, but the evidence from this study suggests it flows in a more focused manner, much like rivers. The way in which water flows beneath the ice sheet strongly influences the speed of ice flow. Vast channels such as this have been observed elsewhere, but their formation has been credited to purely oceanic processes rather than meltwater flowing out of the grounded ice sheet. Advertisement

‘The meltwater feedback cycle under the ice shelf will only slow down once the shelf has collapsed, or no more glacial ice flows in from inland to take its place,’ said co-author and AWI model designer Dr Ralph Timmermann.

‘So we’re talking about processes that will continue over several centuries.’

And, in the Amundsen Sea in western Antarctica, the researchers say the process has already begun.

‘When it comes to the Amundsen Sea, where warm water has already reached the continental shelf and even the grounding line of some ice shelves, we can safely say that this inflow of heat cannot be stopped; the climate regime has already taken place,’ Hellmer said.

‘In other words, the losses of mass of the West Antarctic Ice Sheet will intensify – just like the models predict.’