Loss of summer sea ice in ‘Last Ice Area’ is imminent, study says

Summer sea ice disappeared in the Arctic’s “Last Ice Area” about 10,000 years ago, a new study suggests.

Temperatures then were only slightly warmer than they are today, signalling that the region may no longer have year-round ice within a few decades.

The Last Ice Area lies north of Greenland and the Canadian Arctic archipelago. It currently holds the oldest, thickest sea ice in the Arctic Ocean. Climate models project that the region will be the last stronghold of year-round sea ice as the climate warms, making it a refuge for species that depend on sea ice.

There are signs that the area is changing. Open water has been observed north of Greenland and Ellesmere Island in recent years, said Henrieka Detlef, a paleoclimatologist at Aarhus University in Denmark, who was involved in the new study.

South of the Last Ice Area in Nares Strait, ice arches that typically block the flow of sea ice have been collapsing earlier, she said. As a result, more multi-year ice – which has survived at least one summer – can be flushed out into Baffin Bay.

Some research suggests the Last Ice Area has seen ice-free summers before. Modelling studies point to an Arctic-wide transition from year-round to seasonal sea ice during the early Holocene, for example, a warm period roughly 10,000 years ago. Warming during this period occurred naturally due to changes in the Earth’s orbit.

The new study adds to the growing body of evidence. It draws on two marine sediment cores from the Lincoln Sea, which lies within the Last Ice Area.

Detlef said that, to her knowledge, the cores are unique.

“We don’t have any other cores from that area that reach that far back in time,” she said.

Signs of sea ice

The team collected the sediment cores during a 2019 research expedition. They then analyzed samples from the cores in a lab, looking for molecules that signal a change in ice conditions.

A molecule known as IP₂₅ is produced by algae that live within sea ice, Detlef said. Since the algae need both ice and light to survive, a low level of this biomarker could either indicate a lack of sea ice or thick sea ice that limits light transmission, she explained.  

To decipher which of these scenarios occurred, Detlef and her colleagues measured a second type of molecule produced by algae found in the open ocean.

High levels of these second molecules, called sterols, but an absence of IP₂₅ probably means there was no sea ice at the time, she said. Detecting both IP₂₅ and sterols, meanwhile, points to a seasonal sea ice environment.

Sediments from about 11,300 to 9,700 years ago have elevated concentrations of both types of molecules, the researchers found. This indicates a period of seasonal sea ice, they reported in March in the journal Communications Earth and Environment.

After 9,700 years ago, however, both IP₂₅ and sterols dropped to low concentrations, pointing to the re-establishment of year-round sea ice.

Comparing their findings to temperature records reconstructed from ice cores at the nearby Agassiz ice cap on Ellesmere Island, the researchers found that the transition to seasonal sea ice coincided with heightened temperatures during the early Holocene.

Back then, air temperatures were 3.6C warmer on average than the pre-industrial period from 1850 to 1900, according to the temperature record. As of 2009, the latest year in the record, the region had warmed by an average of 3.1C compared to pre-industrial times, the researchers reported.

“We’re really moving into that window of temperatures again that we had in that region during the early Holocene,” Detlef said.

In the most recent samples from the sediment core, she and her colleagues also saw sterols and IP₂₅ beginning to rise, signalling that the transition is already under way.

Detlef notes that the sediment cores were taken relatively close to the coast, not in the centre of the Last Ice Area. It’s possible that in the past, year-round sea ice survived in the central parts of the Last Ice Area, she said.

But even if summer sea ice only disappeared along the coast, the remaining ice would be vulnerable to being flushed out of the Arctic – essentially moving the ecosystem in the same direction.

Far-reaching effects

A shift to seasonal sea ice in the Last Ice Area would have consequences on local, regional and global scales, said Audrey Limoges, a paleoceanographer and associate professor at the University of New Brunswick, who was not involved in the research but is currently leading a project investigating the effects of melting ice in the Lincoln Sea.

“It’s a very significant region,” she said.

Summer sea ice typically reflects sunlight. As it melts, the ocean absorbs more energy from the sun, which can accelerate warming, Limoges said. Melting ice also releases freshwater, which can affect global ocean circulation.

From a more regional perspective, Limoges said, the disappearance of summer sea ice in the Last Ice Area could be harmful to many species that rely on the ice. The loss of year-round sea ice in the Lincoln Sea might also affect areas downstream, such as Pikialasorsuaq, or the North Water Polynya – the most biologically productive region in the Arctic, she said.

According to Detlef, the change could reverberate up the food chain and have consequences for humans.

“Even though we do not quite understand the entire implications for the ecosystems yet, I think when the sea ice is gone, it will be a complete disruption of the Arctic ecosystems as we know them,” she said.

Avoiding the loss of summer sea ice in the region will require swift action, Detlef said. With the Arctic warming roughly four times faster than other regions, the transition to seasonal sea ice would occur even if global temperatures rose by 2C, the researchers reported.

According to the latest IPCC report, released in March, existing and planned fossil fuel infrastructure is already projected to produce enough emissions to warm the planet by 2C. Limiting warming to 1.5C this century is only possible if greenhouse gas emissions peak in the next two years, the report states.

Although Detlef and her colleagues project that summer sea ice could disappear within a few decades, the exact timing of the shift is still unclear. Detlef said that timing is something she would like to pinpoint in future work.

“I think sometimes the urgency is not quite clear,” she said.

Narrowing down when summer sea ice is expected to disappear might help highlight just how few years are left, she said.

This article is produced under a Creative Commons CC BY-ND 4.0 licence through the Wilfrid Laurier University Climate Change Journalism Fellowship.