Between 116,000 and 129,000 years ago, sea levels were 20 to 30 feet higher than they are today, inundating much of what is the modern day coastline and flooding entire islands. Exactly why the waters rose so high during that time, the Eemian period, however, has been a mystery. But new research indicates that warming temperatures caused the West Antarctic Ice Sheet to collapse, a scenario that concerns scientists under today’s conditions.
Researchers long thought that the high water during the Eemian period was caused by the collapse of the Greenland’s ice sheet. Paul Voosen at Science reports that recent geological evidence shows that Greenland’s ice was intact and grinding along during the period, relieving it of blame for sea rise. The next most likely culprit, then, was the West Antarctic Ice Sheet, a massive, unstable crust of ice on the southern continent.
To figure out if the area sloughed off its ice during the Eemian, glaciologist Anders Carlson of Oregon State University and his team looked at archives of marine sediment cores drilled off the coast of the ice sheet to determine the chemical signatures of silt deposited by three major sources: the Antarctic Peninsula, the Amundsen province near the Ross Sea and the area in between, around the particularly vulnerable Pine Island Glacier.
They then looked at a sediment core from the Bellingshausen Sea, where a stable current carries silt from all those sources and deposits them together, creating a timeline of the ebb and flow of the glaciers. When they examined the silt deposited during the Eemian, they saw that the material from Amundsen and Pine Island slowly disappear, leaving only the silt from the Antarctic Peninsula. Their data was presented at the the fall meeting of the American Geophysical Union.
The most logical interpretation is that the ice in those two areas stopped flowing or disappeared, while the glaciers in the mountains of the Peninsula were able to persist.
“We don’t see any sediments coming from the much larger West Antarctic Ice Sheet, which we’d interpret to mean that it was gone,” Carlson tells Voosen. “It didn’t have that erosive power anymore.”
It may not take much of a temperature change to destabilize and cause the West Antarctic Ice Sheet to collapse, as it’s currently showing signs of stress. Then again, what happened in the Eemian is not a perfect analogue for what’s taking place today. It is considered the last interglacial period, a time when the massive lobe-like glaciers that scoured the northern hemisphere retreated for a time. During that period, summer temperatures in the Arctic spiked and were even warmer than they are today. However, those changes were not driven by human-induced climate change.
Instead, it’s believed that a slight change in Earth’s orbit and spin axis created warmer temperatures in the northern hemisphere causing changes around the world, explains Nathaelle Bouttes at the National Centre for Atmospheric Science in the U.K.
Whether or not the Eemian is a perfect model, it appears Antarctica under stress today. Douglas Fox at National Geographic reports the continent has shed three trillion tons of ice since 1992, most of that from the West Antarctic Ice Sheet, with ice losses tripling in the last quarter century. A study earlier this year also indicates the ice may be more unstable than we thought, with another major retreat taking place 10,000 to 12,000 years ago, when the world was cooler than average temperatures today.
But scientists aren’t just seeing movement in the West. The East Antarctic Ice Sheet, long thought to be the stable side of the continent, is also showing signs of ice loss. Alexandra Witze at Nature reports that glaciologists recently reported four major glaciers in Vincennes Bay are thinning at accelerating rates as they encounter warmer sea water. That’s on top of the increased flow of the massive Totten Glacier. Together, the Totten and Vincennes glacier systems hold enough ice to raise sea level 30 feet.
According to a study from NASA released over the summer, ice melting off Antarctica is already having a measurable impact on sea level, increasing global sea levels by 0.3 inches since 1992—with 0.12 inches of that rise coming just since 2012. If all of the ice in Antarctica melted, sea level would rise an immense 190 feet. That may seem far-fetched, however, at least one recent study in Science Advances suggests if we burn all the fossil fuels available we could indeed melt the entire ice cap.
Voosen reports that researchers hope to gain clarity about the Eemian period from additional cores scheduled to be drilled off Antarctica early next year. But no matter what they find, things in this period aren't looking good.