Canada's last epishelf lake drained into the Arctic Ocean following the 2020 breakup of the Milne Ice Shelf and will not recover, a new study confirms.
Epishelf lakes form when an ice shelf acts as a dam, trapping a layer of freshwater floating above seawater connected to the ocean. The Milne Fiord epishelf lake, located on northern Ellesmere Island in Nunavut, supported freshwater microorganisms near the surface and marine species below.
In July 2020, the Milne Ice Shelf broke apart, losing 45 per cent of its area and removing the barrier that held the freshwater in place.
Drawing on a decade of ocean measurements, satellite imagery, and field observations collected before and after the breakup, researchers from UBC, University of Alberta, Université Laval and Carleton University reconstructed the lake's disappearance.
Their findings show that the freshwater layer began escaping immediately after the collapse and had mostly vanished by autumn 2020.
"The ice shelf and lake had been thinning for decades, but the 2020 breakup was the last straw. The lake drained within months," said study author Dr. Jérémie Bonneau, a professor of civil and water engineering at Université Laval who conducted part of the research during his PhD at UBC.
The first field measurements collected after the breakup showed that by July 2022, brackish water had fully replaced the lake's distinct freshwater layer. Annual monitoring since then has found no sign of recovery.
"Epishelf lakes can signal when an ice shelf is under stress, and that's what we saw here," said co-author Dr. Bernard Laval, a professor of civil engineering at UBC who leads its environmental fluid mechanics research group. "The data showed the ice shelf was failing. Once the ice is gone, the ecosystem goes with it. There's no coming back."
"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," said co-author Dr. Andrew Hamilton, a research scientist at the University of Alberta who completed his PhD research at Milne Fiord. "When the ice shelf broke apart, that unique ecological structure disappeared."
Dr. Derek Mueller, a professor of geography and environmental studies at Carleton University, established the research program that tracked the ice shelf and lake through years of accelerating change.
"There are much easier places to conduct research, but understanding change in the High Arctic requires returning year after year," said Dr. Mueller. "When we began this work, we knew the ice shelf and epishelf lake were vulnerable and designed this project to monitor the transition of the fiord from one with an epishelf lake and an ice shelf to one that is seasonally ice-free. We anticipate further profound changes in the coming years."
The research team included co-authors Silas Pijamini and Joseph Shoapik from Ausuittuq (Grise Fiord), who have participated in fieldwork since 2022.
A decade of data captures the loss
Published in Scientific Reports , the study provides the first complete reconstruction of the lake's drainage and its transformation from a freshwater ecosystem into a marine environment.
Researchers analyzed data from instruments anchored in Milne Fiord, along with annual water profiles, satellite imagery and field observations. Instruments left in place during the COVID-cancelled 2020 field season recorded the lake's rapid salinization, though researchers could not retrieve the data until two years later.
The study found that freshwater entering Milne Fiord is now flushed directly into the ocean because the remaining ice shelf can no longer contain it. Re-establishing the lake would require the ice shelf to recover, which is not possible under the current climate trajectory.
Loss reaches the Last Ice Area
The Milne Ice Shelf lies within the Last Ice Area, a region expected to retain perennial sea ice longer than anywhere else in the Northern Hemisphere. It is also within the Tuvaijuittuq Marine Protected Area, whose name means "the place where the ice never melts" in Inuktitut.
The loss of the lake shows that even this potential refuge for ice-dependent ecosystems is undergoing rapid change.
"These systems took thousands of years to form and were lost in months," said Dr. Bonneau. "On any human timescale, they are not coming back."
Interview languages: English (Bonneau, Hamilton, Laval, Mueller), French (Bonneau, Laval)
