A new study suggests that Antarctica’s melting ice sheets may be retreating much faster than previously thought.
The evidence comes from undersea traces off Norway, which documented the melting of the European ice sheets thousands of years ago.
Today, the fastest retreating glacier in Antarctica has been observed, retreating up to 30m per day.
However, if they accelerate, the additional meltwater will have a significant impact on sea level rise around the world. Global sea levels have already risen by almost 1 cm since 1990s due to climate change-induced ice loss from Antarctica. Researchers have found that the maximum retreat of the Norwegian foil is more than 600 m per day.
“This is something we could see if we continue with the upper estimates for temperature rise,” explained Dr Christine Batchelor from Newcastle University, UK.
Dr. Batchelor and colleagues report their research in this week’s issue of Nature.
The team explored most of the seafloor off central Norway. 20,000 years ago, the region witnessed the threat and melting of the massive Northern European ice sheet.
The sheet’s past existence is carved into more than 7,600 parallel ladder-like ridges, carved into the muddy deposits of the Norwegian Sea. These corrugations are less than 2.5m high and are spaced about 25m to 300m apart. Scientists interpret the ridges as features produced in the ice zone.
This is the zone where glacial ice flowing from land to sea becomes buoyant and begins to float. Waves are created when the ice at the point repeatedly strikes the sediment with the daily ebb and flow of the tide.
Ice must be receding to create and store patterns (advancing ice destroys ridges). A tide clock therefore indicates the speed of this reversal.
The team’s results show that the former European ice sheet was retreating rapidly at rates of 55 to 610 meters per day. Importantly, the highest velocities were observed where the seafloor was relatively flat. These are places where the thickness of the ice on top tends to be more uniform and less melting is required to float and retreat the ice.
Similar undulations have been found on the seafloor around Antarctica, but the examples are rather limited. The Norwegian study area is much larger, giving a clearer picture of how quickly the ice would retreat in a warmer climate. Today, scientists use satellites to monitor the glacial grounding zone that borders the oceans of Antarctica. The probe can track where ice rises and falls with the tides
The Pope Glacier in the west of the continent experienced the fastest retreat, with an average daily velocity of 33 m recorded over 3.5 months in 2017.
But Pope is not one of Antarctica’s most powerful glaciers. Scientists are more interested in giants like Thwaites. The ice block is the size of Britain and, if it melts completely, could raise global sea levels by half a meter.
“From Thwaites’ current landline he is 4 km inland, with a channel that looks like a channel with a flat bottom. This is the perfect environment for the buoyancy-induced contraction process,” says co-author Dr. Frazer Christie of the Scott Polar Institute (SPRI), University of Cambridge, UK. “This is a small area compared to the entire Thwaites River Basin, but even a very rapid retreat of short duration will affect the future dynamics of the glacier.”
Dr. Batchelor and Dr. Christie say their team’s observations call for improved computer models trying to predict the future of Antarctica in a warming world. At present, these models lack important details about ice behavior.
“But this is why we look into the geological past to tell us what’s possible. Yes, we have satellites, but their records are very short – only 40 years or so,” commented co-author Prof Julian Dowdeswell, also from SPRI.
“Importantly, the geological record is something that has actually happened. It’s an ‘observation’ in the real world, not just in the computer model world,” he told BBC News.