The ice downstream of the glaciers in northeast Greenland is very important for their stability, but a third of this ice has disappeared since 1978.
By scraping the rock, the ice tongues flow from the continent towards the sea, where they eventually form floating platforms, natural barriers that slow down the flow of glaciers. In the most extreme and isolated climate in northeast Greenland, thirty-five percent of their volume has disappeared since 1978.
Romain Millan, geophysicist at CNRS and ice flow specialist at Grenoble Alpes University, and his colleagues from Greenland, Denmark and the USA, have studied their contemporary history using satellite observations, and published their results in Nature Communication on November 7.
They observed eight floating ice tongues and assessed their volumes. “We found that three of these platforms collapsed around the 2000s, and then in 2014, half of one platform went completely into the sea,” explains the article’s lead author. “An unusual event that is outside the natural cycle of a glacier.”
Between 2003 and 2009, three of these eight ice shelves collapsed completely, including the one on the Zachariæ Isstrøm glacier. Without this natural barrier downstream, upstream ice flows faster to the sea. “By looking at the amount of ice from the ice cap in the ocean before and after the collapse, we realized that it had almost doubled,” explains Romain Millan.
This acceleration in ice flow results in a more rapid rise in sea levels, which is a major concern for coastal populations. The Greenland ice cap alone would represent a rise of 2.1 metres if it were to disappear completely.
Changes in climatic conditions and winds have favored the arrival of warm subtropical waters in the continental areas on which the glaciers rest. “From the 2000s onwards, images are precise enough to reconstruct underwater melting, and we can see that it is very significant and correlated with ocean warming,” he adds.
The vulnerability of these glaciers lies at their base, in the last few meters that touch the ground before the tongue of ice floats on the sea, i.e. the grounding line. “If it lies on a slope inclined towards the continent, formed by the lowering of the bedrock under the weight of the Greenland ice sheet, the retreat of the glacier can accelerate until it regains relief and stabilises”, describes the author.
In the rest of Greenland, the rest of the ice cap’s glaciers have been suffering the effects of climate change since the mid-1980s. “With this study, we’ve shown that it’s now the entire ice cap that is bearing the full brunt of global warming,” concludes Romain Millan.
Camille Lin, PolarJournal
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