In July 2020, a giant Arctic shelf collapsed in Canada, losing more than 40% of its surface area in just two days. The Milne Ice Sheet acted as a dam, trapping a layer of freshwater above the Arctic Ocean. Within months of its breakup, that freshwater lake drained into the ocean and completely disappeared.
In a new study, a team of scientists reconstructed the death of Canada’s last epishelf lake as warming temperatures take their toll on the unique Arctic ecosystem. The findings, published in the journal Scientific Reports, highlight the loss of the Milne Fiord lake as a sign of the vulnerability of Arctic sea ice against climate warming.
Washed away
Epishelf lakes are rare bodies of fresh water that float directly above the denser saltwater of the ocean. The freshwater is trapped in place by a floating ice shelf. A unique ecosystem forms in the lake, with freshwater organisms thriving near the surface while marine species live in the ocean below.
The Milne Fiord epishelf lake, located on northern Ellesmere Island in Nunavut, was the last large epishelf lake still standing in the Canadian Arctic. The lake formed when the Milne Ice Sheet created a dam blocking the mouth of the fjord, and meltwater runoff from the glaciers collected behind it.
The Milne Ice Sheet was once the last fully intact ice in the Canadian Arctic, but it sadly collapsed six years ago and shrank by around 30 square miles (80 square kilometers). With the collapse of the ice sheet, the epishelf lake didn’t stand a chance.
“Epishelf lakes are remarkable because a freshwater ecosystem sits directly above a marine one, separated only by a thin boundary between fresh water and salt water,” Andrew Hamilton, an arctic oceanographer at the University of Alberta and a co-author of the study, said in a statement. “When the ice shelf broke apart, that unique ecological structure disappeared. It was the last of its kind in Canada.”
Chronicle of demise
The scientists behind the new study used satellite imagery, field observations, and ocean measurements to chronicle the lake’s drainage.
The team had been monitoring changes to the ice sheet since 2011, tracking its accelerating transformation amidst warming temperatures. “The ice shelf and lake had been thinning for decades, but the 2020 breakup was the last straw,” Jérémie Bonneau, a professor of civil and water engineering at Université Laval and co-author of the study, said in a statement. “The lake drained within months.”
By autumn 2020, the lake and its unique ecosystem had completely vanished. The ice sheet that contained the epishelf lake will not recover under the current climate trajectory, the study notes. “These systems took thousands of years to form and were lost in months,” Bonneau said. “On any human timescale, they are not coming back.”
The team recalls drilling into the lake’s outflow channel below the ice shelf in 2017 and seeing “a robust marine ecosystem with brittle stars, sea anemones, scallops, etc., all living in complete darkness in a channel at the base of the ice shelf,” Hamilton said. “My kids are never going to see that kind of ice shelf and lake system in their lifetime. It’s the end of an era.”
Read the full article here
