The retreat of the Antarctic ice sheet could be happening faster than previously thought

Scientists monitor rates of ice sheet retreat to better estimate contributions to sea level rise. Antarctica and Greenland have lost more than 6.4 trillion tons of ice Since the 90s, raising global sea levels by at least 0.7 inches (17.8 mm). The two ice sheets together are responsible for more than a third of the total sea level rise.

The rapid retreat found on the Eurasian ice sheet far outpaces the fastest-moving glaciers studied in Antarctica, which have been measured to retreat as fast as they can. 160 feet per day. Once the ice recedes toward the groundit rises from the sea floor and begins to float, allowing it to flow faster and increasing its contribution to sea level rise.

If air and ocean temperatures around Antarctica rise as expected and match those at the end of the last ice age, researchers say ice traveling back hundreds of feet a day could lead to the collapse of recent glaciers sooner than thought. previously. This could be devastating to global sea levels.

Lead author Christine Batchelor said, “If temperatures continue to rise, the ice may have melted and thinned from above and below, until you end up with a scenario that looks more like what we have.” [off] Norway after the last glaciation. “

In the new study, Batchelor and her colleagues analyzed earlier layers of two major ice streams across the Norwegian continental ice shelf dating back between 15,000 and 19,000 years ago. Using shipborne images, the team calculated retraction rates by studying wave-like patterns of ridges along the seafloor. They determined that the regular ridge patterns may have been created because the glacier front bounces off the sea floor from daily tides. The team mapped the spacing between more than 7,000 edges to calculate the regression rate.

“The ice sheet can move over several kilometers a day, touching the high tide which results in these ridges as it goes, kind of bobbing up and down on the tide,” said Batchelor, a physical geographer at the University of Newcastle. .

The team found retreat rates range from 180 to 2,000 feet per day. The extreme rates only lasted on a scale of days to months and probably couldn’t last much longer. If the ice sheet retreats about 600 meters a day for a year, Batchelor said, there probably won’t be any ice left.

“This is not a model. This is a real observation. And it’s honestly scary. Even for me,” Eric Regno, a glaciologist who was not involved in the study, said in an email.

In the past, one of the fastest rates of retreat ever detected for glaciers was in the Pope Glacier in West Antarctica, a smaller glacier very close to the massive Thwaites Glacier, nicknamed the “Resurrection Glacier” due to its relatively large melt contribution to the sea level above. . During a period in 2017, based on satellite accountsPope Glacier retreated at a rate of about 105 feet (32 m) per day. That’s pretty fast — but still something like rates of 2,000 feet per day, the study found for the Eurasian ice sheet.

The higher rate found in the study released Wednesday is about 20 times higher than any rate of retreat measured from satellites, Batchelor said, and 12 times faster than any rate of retreat inferred from similar seafloor landforms.

Bob’s rate of retreat has now slowed, and similarly, for the Eurasian ice sheet, an extremely rapid pulse of retreat would have been temporary. Still worrying, Regno, one of the scientists who published a paper in 2022, said Pope’s icy retreat documented.

Ice sheets are retreating rapidly today. [especially] In Antarctica,” said Regno, a scientist at the University of California, Irvine. “But we’re seeing traces on the sea floor that suggest the decline could be much faster, much faster, and it’s a reminder that we haven’t seen everything yet.”

Not all layers of ice are very susceptible to this speed regression rates. The study found that the fastest melting occurred in the flat areas of the ice sheet.

Batchelor and her colleagues hypothesized that the rapid rates of retreat occurred across the flat regions because the ice sheets were more buoyant compared to the steeper ice slopes. She said the ice sheet of uniform thickness and flat was indeed close to floating, as it was sitting on the surface of the sea floor. Simple melting may push the flat ice layer up and move it toward the groundlike a large ice cube that can float from the ocean floor with enough gentleness.

She explained that it would be difficult to remove a slanted ice sheet from the sea floor. The slanted ice surface on top of the ice sheet may increase “driving stress,” which may push the ice more forcefully into the ground. Steep ice sheets are less likely to rise from the sea floor during tidal movements and become buoyant.

Batchelor said the findings are troubling for many of Antarctica’s current glaciers near flat ice sheets. Thwaites Glacier, for example, is mounted on a ridge but has a flat area of ​​its bottom only four kilometers inland. If the ice were to retreat to this flat area of ​​its bottom, Batchelor said, “we could very well see one of these pulses of really rapid retreat happening in that area.”

University of South Florida marine geophysicist Alastair Graham, who was not involved in the study, said he was “cautious about drawing direct lines” between how the last ice sheet over Norway melted some 15,000 years ago and what’s happening in Antarctica now — in part because sea level It was rising faster at that time.

“This may be a critical driver of rapid change in the past that we will not see repeated on the same scale now or in the near future,” he said. Norway is also located in a much milder place than Antarctica and would have had an ice sheet that was more vulnerable.

In any case, he said “discovering that ice sheets are capable of very rapid change as they essentially move away from their bed is exciting” and is in line with Search his team. Similarly, when analyzing ridges along the seafloor near Thwaites, Graham was “astonished” to document that the glacier has pulses of retreat of up to 32 feet (10 m) per day at the ice front. He agrees that the glacier is likely to experience “pulses” of rapid retreat in the coming decades to centuries, but is not sure if it will be on the order of hundreds of meters per day.

However, glaciologist Andrew Shepherd of Northumbria University, who was not involved in the study, said the speeds of retreat of the Eurasian ice sheet may not actually be all that different from what would happen today. That’s because the new research is based on seafloor markings that would have occurred twice daily. By contrast, today’s satellites are generally used to make annual measurements of change, Shepherd said, so they’re not as good at detecting rapid periods of change, but they are relatively short-lived.

“I do not think so [the new research] It changes what we think about.