(CN) — New research shows that by the end of the last Ice Age, the ice shelves around the Antarctic coastline were retreating at a baffling speed of more than 160 feet per day, much faster than the rates scientists observe today.
In a study published Thursday in the journal Science, researchers from the Scott Polar Research Institute at the University of Cambridge used the patterns of wave-like ridges on the Antarctic seafloor to find how fast ice sheets retreated about 12,000 years ago through regional deglaciation brought on by the end of the Ice Age.
The ridges appeared when the sheets started to float, causing ice to squeeze sediments onto the seafloor as the tides moved.
The team captured images of this submerged landscape at sub-meter resolution made possible by an autonomous underwater vehicle (AUV) working about 196 feet above the seabed.
Today, we have modern satellites that can gather detailed information about the retreat rates of ice around Antarctica, but this data only goes back a few decades. But by using the seafloor ridges to obtain the fastest speed an ice sheet can retreat, they found the ancient ice sheets retreated almost 10 times faster than the maximum observed rates today.
“By examining the past footprint of the ice sheet and looking at sets of ridges on the seafloor, we were able to obtain new evidence on maximum past ice retreat rates, which are very much faster than those observed in even the most sensitive parts of Antarctica today,” said Julian Dowdeswell, director of the Scott Polar Research Institute and lead author of the study, in a statement.
The institute’s Weddell Sea Expedition conducted the study. Leading scientists set out last year for the expedition for research and to find Sir Ernest Shackleton’s doomed ship Endurance.
Although the conditions of the sea ice prevented them from getting images of the Endurance, they were able to acquire other scientific observations, like mapping of the seafloor close to the Larsen Ice Shelf, east of the Antarctic Peninsula.
Researchers sought to investigate the present and past form and flow of the ice shelves, which act as a sort of buttress against ice flow from inland. With the use of drones, satellites, and AUVs, the research team was able to study the ice conditions in the Weddell Sea in never-before-seen detail.
These buttresses have been weakening, however, along with much of the ice in these polar regions.
This can be most evidently seen in the collapse of the Larsen A and B ice shelves in 1998 and 2002 when roughly 1,250 square miles of ice fragmented and fell in little over a month.
This thinning occurs when warm water currents eat away at the ice shelf from below, as well as when summer air temperatures rise and melt the ice from above. Weakened ice shelves are unable to hold back glaciers from inland, which then flow faster to the sea resulting in a faster retreat rate.
Using the AUVs, the team was able to collect data on historic ice shelf fluctuations based on the geological records on the Antarctic continental shelf. They identified the pattern of wave-like ridges on the seafloor, with each reaching about three feet high and spanning about 65 to 82 feet apart.
These ridges date back to the end of the last great deglaciation of the Antarctic continental shelf, roughly 12,000 years ago. The researchers determined they must have formed at what was once the grounding line — the zone where grounded ice sheets begin to float as an ice shelf.
“By examining landforms on the seafloor, we were able to make determinations about how the ice behaved in the past,” Dowdeswell said. “We knew these features were there, but we’ve never been able to examine them in such great detail before.”
The team found that the ridges formed when the ice lifted off the seafloor and squeezed out sediments with the movement of the tides, creating patterns like rungs on a ladder as the ice retreated. By measuring the distance between the ridges and factoring a 12-hour high and low tide cycle, the researchers calculated how fast the ice was retreating.
They concluded that the ice had been retreating as much as 130 to 160 feet per day during this time, totaling more than six miles in a whole year. Comparing that to modern satellite images of Pine Island Bay in Antarctica, for example, even the fastest retreating grounding lines only retreat about just under a mile.
“The deep marine environment is actually quite quiet offshore of Antarctica, allowing features such as these to be well-preserved through time on the seafloor,” Dowdeswell said. “We now know that the ice is capable of retreating at speeds far higher than what we see today. Should climate change continue to weaken the ice shelves in the coming decades, we could see similar rates of retreat, with profound implications for global sea level rise.”