Pleistocene glacial ice discovered in the permafrost of the Canadian Arctic
On Bylot Island in the Canadian Arctic, bodies of ice have been hidden in the permafrost since the early Pleistocene – well protected from external influences and several warm periods. The age of the ice is estimated to be more than 770,000 years.
Finds of glacial ice in permafrost are no longer a sensation. Researcher Dr. Stéphanie Coulombe from Polar Knowledge Canada and her team were therefore not too surprised when they found preserved glacier ice buried in permafrost on Bylot Island in Nunavut, Canada, in 2009, as she reported in an email to Polar Journal AG. The ice only became visible after a landslide on a mountain plateau due to the thawing permafrost.
It was already known from previous studies that large chunks of ice can be found in the permafrost in the Arctic (in Canada, Alaska and Siberia) and also in the Antarctic. Dr. Coulombe and her team had also found exposed glacial ice in the valley floor of the same region on Bylot Island. She explains that the glacial ice trapped in the permafrost typically dates from the last ice age, when large parts of the Arctic were covered by the Laurentide ice sheet, and is between 20,000 and 26,000 years old. They therefore assumed that the ice they discovered was also younger ice.
Possibly older than a million years
But when the team determined the age of the sediments overlying the ice, the surprise followed, as Dr. Coulombe describes: “We detected a magnetic reversal in the sediments, and the last major reversal occurred 780,000 years ago — implying that the ice must be even older. At that moment, we could hardly believe it! The Canadian Arctic is so vast—what were the odds of making such a discovery during that specific summer?”
In their study, which was published in the journal Geology in January, the researchers estimate the age of the two huge ice bodies, which were around 8 and 10 meters wide and more than 3 meters thick, to be at least 773,000 years old.
The exact age of the ice is not known, but by dating the layers above and below it, the team was able to narrow down the period from which the glacial ice originated.
It may even be significantly older than a million years, as the layer below suggests. There lie the fossilized remains of a forest that shaped the island’s landscape 2.8 to 2.4 million years ago.
Survived several warm periods
The glacier ice has therefore survived several climatic changes with warm periods in the past – thanks to the overlying sediment layer, which is around 3 meters thick, and the continuous permafrost conditions, which have allowed the ice to persist for a very long time.
The current rapid warming of the climate and thaw slumps now seem to be sealing the fate of this very old ice.
“Permafrost contains unique archives, including ancient glacier ice. While past climate and environmental conditions have mostly been studied through ice cores from the Greenland Ice Sheet, the abundance of glacier ice of various ages in permafrost across the Arctic provides additional opportunities to investigate these conditions in other deglaciated Arctic and northern regions. However, modern climate warming and the accelerated rates of thermokarst now threaten to destabilize these valuable ground-ice archives.”
Dr. Stéphanie Coulombe
Pollen and air bubbles in the ice
In addition to pollen from trees and shrubs and fragments of diatoms, the ice also contains air bubbles, albeit comparatively few. The latter make it a valuable archive with information about past climates and the environment, just like the ice of present-day glaciers and ice sheets, which currently receive more attention than ice in permafrost.
However, the amount of research on permafrost ice as a paleoarchive is increasing and Dr. Coulombe thinks that glacial ice trapped in permafrost will receive similar attention.
How was the ice trapped in the permafrost?
Dr. Stéphanie Coulombe explains that sediment can be deposited on the remaining ice, particularly at the edges of glaciers, for example by melt water run-off or falling rocks. A thick layer of sediment insulates the ice and limits its melting so that it can separate from the active glacier over time. In the Arctic, this ice was preserved by the permafrost that formed after the glacier retreated under the cold and dry conditions.
“The formation of these ice-covered landforms follows a typical sequence, where the ice is first buried under enough sediment to insulate the glacier and limit its melting. Over time, large sections of glacier ice become progressively separated from the upper, flowing ice. In the Arctic, after the glaciers retreated, the cold and dry climate allowed permafrost to form, which helped preserve these ice bodies.”
According to Coulombe, older ice deposits are normally destroyed by advancing glaciers. In some regions, however, remnants of very old glacial ice have been preserved. One possible explanation is that during successive ice ages, these areas were covered by less erosive, cold-based ice – ice at the base of the glacier that is completely below the pressure melting point. “This allowed older glacial deposits to be preserved beneath the ice. Alternatively, higher upland areas may have remained largely ice-free during subsequent glacial advances.”
The current warming and the accelerated formation of thermokarst (surface thawing permafrost) threaten to destroy these unique ice archives – and with them valuable information about the climate and environmental changes in the Arctic during the Pleistocene.
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